JP4858342B2 - Catalyst material manufacturing method, gas sensor electrode manufacturing method, and gas sensor manufacturing method - Google Patents

Description

The present invention relates to a method for producing a catalyst material for a gas sensor, a method for producing an electrode for a gas sensor , and a method for producing a gas sensor , which have an effect of promoting a chemical reaction of gas . Examples of the use of the catalyst material include, in addition to the gas sensor electrode, a catalyst-supported metal, a fuel cell electrode, and a combustion heater using heat generated during gas reaction.

  Conventionally, as a catalyst material having an effect of promoting a chemical reaction of gas, for example, platinum (Pt), gold (Au), silver (Ag), iridium (Ir), palladium (Pd), rhodium (Rh), etc. A single noble metal or an alloy made of two or more kinds of these is used (for example, see Patent Document 1).

Further, as a gas sensor having an electrode made of a catalyst material, there are a stack type and a cup type gas sensor (for example, see Patent Documents 2 and 3).
Japanese Patent No. 2541530 JP 2002-181764 A JP 2002-31618 A

  In recent years, there has been a demand for the development of a catalyst material having an improved reaction promoting effect than before.

  For example, in a catalyst material used for purifying exhaust gas of a vehicle, further exhaust gas purification is required as the global warming progresses, and improvement in catalyst performance is required. The combustion heater is also required to be reduced in size by efficient purification, and in the fuel cell, it is necessary to develop not only a highly valuable Pt system but also an alternative material.

  Further, in an oxygen sensor that detects the oxygen concentration in the exhaust gas of a vehicle, which is an example of a gas sensor, the purification of the gas has progressed due to various new developments of a catalyst that purifies the exhaust gas, and the concentration of untreated gas Has fallen. For this reason, conventionally, since the concentration of harmful gas in the exhaust gas was high as described below, it was sufficient if the material consisting of the noble metal or noble metal and oxide of the electrode portion had a certain degree of reaction promoting effect, In recent years, due to the dilution of exhaust gas flowing into the electrode portion of the sensor, there has been a problem that a delay in the reaction of the exhaust gas occurs and the followability of the sensor output decreases.

  Here, FIG. 22 shows an example of the relationship between the oxygen excess rate λ and the sensor output value when Pt is used as the electrode material of the oxygen sensor having catalytic performance. The oxygen excess rate λ is the excess rate of oxygen when a specific gas and oxygen chemically react, and the atomic ratio (molecular ratio) between the specific gas and oxygen is a ratio represented by a chemical reaction formula. In the same case, λ = 1.

On the electrode surface of the oxygen sensor, for example, carbon monoxide (CO) in the exhaust gas reacts with oxygen (O ₂ ) by the catalyst material contained in the electrode to generate carbon dioxide (CO ₂ ). At this time, since the oxygen concentration in the exhaust gas changes, the sensor output value changes in accordance with the change in the oxygen excess rate λ, but when the CO in the exhaust gas has a very low concentration (for example, 50 ppm), FIG. As shown in FIG. 6, there is a problem that the change in the sensor output value due to the change in the oxygen excess rate λ becomes slower than when the CO concentration is high (for example, 1%).

  Therefore, as a method of developing a catalyst material with improved reaction promotion effect than before, the reaction promotion effect is improved by simultaneously replacing a part of the base material atoms constituting the catalyst material with other types of atoms. A method is conceivable.

  However, simply searching for the optimum substituent atom while confirming its effect by experiment, various combinations of substituent atoms are conceivable. Therefore, a catalyst material that easily improves the reaction promotion effect than before. Does not lead to development.

In view of the above point, it is possible to improve the reaction promoting effect than conventional method for producing a catalyst material for the gas sensor, and an object thereof is to provide a method of manufacturing a manufacturing method and a gas sensor of the gas sensor electrode.

  As a result of intensive studies, the present inventor used a calculation that can be easily compared by changing the configuration even at the atomic level of about several tons, and when a part of the base atom is replaced with a substituted atom, It is found that it can be classified into a substitution atom that is easy to adsorb gas just above and a substitution atom that is easy to adsorb gas just above the base atom adjacent to the substitution atom, and material design based on this classification result Thus, the inventors have developed a catalyst material that can improve the reaction promoting effect as compared with the conventional catalyst material.

  Here, whether the gas is likely to be adsorbed directly above the substitute atom or on the side of the base material atom is calculated by substituting the substitute atom in the base material model and placing the gas there. It can be judged by comparing the energy levels. That is, when the energy of both models is compared, the smaller the energy, the easier it is to adsorb.

Therefore, in order to achieve the above object, the present invention is characterized by producing a catalyst material for a gas sensor as follows. That is, first, as a substitution atom, an atom that can be substituted for a part of the matrix atom is selected without breaking the crystal structure of the matrix atom, and the crystal of the matrix atom is maintained while maintaining the crystal structure of the matrix atom. For the structure, a simulation model is created in which a part of the base material atoms is replaced with substitution atoms. Note that maintaining the crystal structure or not destroying the crystal structure means that the classification of the crystal structure remains the same as that of the base material atom such as Pt, and the lattice constant is changed or the arrangement of the atoms is distorted. There is no deviation from it.

  Then, using the simulation model, the first adsorption energy of the gas when the target gas atom or molecule is arranged immediately above the substitution atom, and the target gas atom or molecule are positioned next to the substitution atom. The second adsorption energy of the gas when arranged immediately above the base material atoms is calculated.

  Next, the calculated first adsorption energy and second adsorption energy are compared, and the first adsorption energy is lower than the gas adsorption energy when the first adsorption energy is only the base material atom. Lower substitution atoms are classified into the first group, and substitution atoms having a lower second adsorption energy than the first adsorption energy are classified into the second group.

  Next, based on this classification result, each of the substituted atoms belonging to the first group and the second group is selected, and a part of the base material atoms is substituted with the substituted atoms belonging to the first group and the substituted atoms belonging to the second group. It is characterized by being replaced with.

  As a result, the adsorption energy of the gas adsorbed on the surface of the catalyst material can be lowered compared with the case where a part of the base material atom is substituted with a substitution atom belonging to either the first group or the second group. The gas can be easily adsorbed on the surface of the catalyst material.

  In general, the higher the gas adsorptivity on the surface of the catalyst material, the more the chemical reaction of the gas is promoted. Therefore, according to the present invention, a part of the base material atom is substituted with a substitution atom belonging to one group. As compared with the case of the case, the effect of promoting the chemical reaction of the gas of the catalyst material can be improved.

  It should be noted that, when a substitution atom is selected and replaced from the same group, there is not much difference from the case where one of them is substituted in large quantities, but according to the new method of selecting from a different group of the present invention, the same substitution atom is increased in quantity. In combination with this method, the gas reaction can be further promoted. It goes without saying that a plurality of substituent atoms may be used in the multimerization of substituent atoms.

  In addition, as a means for replacing (solid solution) a part of the base material atoms with substitution atoms, for example, a heat treatment such as firing can be adopted, and other means may be adopted.

  In the present invention, for example, Pt can be used as a base material atom. In this case, Ir, Rh, Pd, Au, Ag can be used as a substitution atom, and when CO is selected as a gas, these can be used. Among them, Rh and Ir are classified into the first group, and Ag, Au and Pd are classified into the second group.

  Further, in the present invention, specifically, as a method for replacing (solid solution) a part of the base material atoms with a replacement atom, for example, the base material and a replacement atom belonging to one of the first and second groups are included. After firing the first substitution material and dissolving the first substitution material in the base material, a second substitution material containing a substitution atom belonging to the other of the first and second groups is formed on the base material surface. Then, by firing and dissolving the second substitution material in the matrix, a part of the matrix atoms can be replaced with substitution atoms belonging to the first group and substitution atoms belonging to the second group. preferable.

  At this time, as a film forming method, there are various methods such as ion vapor deposition, sputtering, and CVD, and a method that can be used for each substituent atom may be used.

  Further, in the present invention, specifically, for example, after firing the base material and the first substitution material containing a substitution atom belonging to the first group, and dissolving the first substitution material in the base material, By forming a second substitution material containing a substitution atom belonging to the second group on the surface of the matrix and firing it, by dissolving the second substitution material in the matrix, a part of the matrix atoms, It is preferable that the substitution atom belonging to the first group is substituted with the substitution atom belonging to the second group.

  In the present invention, specifically, for example, a material composed of Pt is used as the base material, a material containing at least one of Rh and Ir is used as the first replacement material, and Ag is used as the second replacement material. It is preferable to use a material containing the same.

  Further, as a specific example of the present invention, for example, when the second replacement material is formed on the surface of the base material, it is formed on the surface of the base material by forming a film while covering a part of the surface of the base material with a mask material. It is preferable to partially deposit the second substitution material to expose the first substitution atoms and the base material.

  As another specific example of the present invention, for example, after the second replacement material is dissolved in the base material, the base material after the solid solution is adjusted in order to adjust the component ratio in the vicinity of the surface of the base material. It is preferable that the surface of the base material is shaved so that the base material or the first replacement material is partially exposed on the surface.

  Moreover, the electrode of a gas sensor can be formed using the catalyst material manufactured by the manufacturing method of the catalyst material as described in any one of Claims 1 thru | or 7. For example, by applying the present invention to the manufacture of an oxygen sensor electrode, the response of the sensor output due to a change in the oxygen excess rate λ can be improved, and the change in the sensor output value due to the change in the oxygen excess rate λ is slowed down. Can be suppressed.

(First embodiment)
In the present embodiment, an electrode catalyst material for an oxygen sensor that detects an oxygen concentration in exhaust gas will be described as an example. In the present embodiment, the optimum combination of substitution atoms when a part of the base material atoms constituting the catalyst material is substituted with a plurality of substitution atoms is examined by simulation. Thereafter, raw materials are prepared based on the simulation results, and an electrode catalyst material for the oxygen sensor is manufactured.

  Specifically, in order to perform a simulation, first, base material atoms and substitution atoms are selected. At this time, an atom that can be substituted with a part of the base material atom is selected as the replacement atom without breaking the crystal structure of the base material atom. For example, when Pt is adopted as the base material atom, Ir, Rh, Pd, Au, and Ag can be adopted as substitution atoms that can be substituted without breaking the crystal structure of Pt, that is, the face-centered cubic lattice. This is because these atoms stably form a face-centered cubic lattice having the same crystal structure as Pt. Further, except for Ag, other substituted atoms have a relationship of atoms forming a completely solid solution phase equilibrium diagram with Pt, and even if mixed with Pt, they do not eutect and change the crystal structure. It can be dissolved without any problems. Note that the relationship between the atoms forming a completely solid solution phase equilibrium diagram is not a special heat treatment condition, but a material consisting of both atoms as long as the heat treatment condition is the same as the heat treatment condition used to create the phase equilibrium diagram. It means the relationship that can be dissolved in each other. Although Ag is not a complete solid solution system, it is a material that forms a composite phase equilibrium diagram with Pt and has no eutectic point, and has the same face-centered cubic crystal structure as the base material atom Pt. That is, it can be said that there is no risk of breaking the crystal structure of the base material.

  Subsequently, a simulation model in which a part of the base atom is replaced with a replacement atom is prepared for the crystal structure of the base atom. Here, FIGS. 1A and 1B show simulation models used in the first principle calculation.

  As shown in FIGS. 1A and 1B, for example, a part of a 16-solid Pt atom 1 having a close-packed structure is replaced with any desired substitution atom 2 (Ir, Rh, Pd, Au, or Ag). 1), the model replaced is created.

  Subsequently, using the simulation model, the first adsorption energy of the gas when the atom of the gas to be promoted for the chemical reaction is arranged immediately above the substitution atom, and the atom of the gas to be promoted for the chemical reaction are replaced with the substitution atom. The second adsorption energy of the gas when it is arranged immediately above the base material atom located next to is calculated.

In the case of an oxygen sensor that detects the oxygen concentration in the exhaust gas, for example, CO in the exhaust gas reacts with O _{2 on the} surface of the sensor electrode, and this chemical reaction is promoted by the catalyst material in the sensor electrode. Therefore, in this embodiment, CO is employ | adopted as gas used as the acceleration | stimulation object of a chemical reaction, for example. In addition, what is necessary is just to select arbitrarily the gas used as the object of acceleration | stimulation of a chemical reaction so that it may mention later.

  Then, as shown in FIG. 1A, the CO adsorption energy (first adsorption energy) when CO is arranged immediately above the substitution atom 2 and the substitution atom 2 as shown in FIG. The CO adsorption energy (second adsorption energy) when CO is arranged immediately above the adjacent Pt atom 1 is calculated.

  At this time, the periodic boundary condition is taken into the model shown in FIGS. 1A and 1B, and the adsorption energy of CO on the [111] plane of the face-centered cubic lattice formed stably by the base material atoms Pt is calculated. Calculate by first principle calculation. The reason for the [111] plane is that the [111] plane is considered to be a crystal plane on which gas is easily adsorbed. The first-principles calculation is a calculation method that uses quantum mechanics to solve a differential equation including the existence probability of energy and electron density. In the present embodiment, for example, “DMo13” of Accelrys Co., Ltd. is used, and calculation is performed by relative all-electron approximation. The function used is PBE of general gradient approximation (GGA).

  The gas adsorption energy means free energy (energy due to gas arrangement) when the gas is arranged. In the present embodiment, the energy due to the arrangement of CO does not include the energy due to the base material atom Pt or the configuration (structure, periodicity) of the base material atom Pt and its substitution atoms, nor does it include the energy due to the coupling of CO. I did it. That is, the energy of only the base material atom Pt or the base material atom Pt and its substitution atom or the energy of CO alone is calculated, and [when the CO is arranged on the base material atom Pt or the base material atom Pt and its substitution atom. By subtracting [the energy of only the base material atom Pt or the base material atom Pt and its substitution atom] and [the energy of only CO] from the energy, the energy element due to the adsorption of CO on the desired material surface was extracted. This is the CO adsorption energy.

  In this embodiment, before calculating the adsorption energy of CO, the following two points were calculated in advance and the calculation results were compared. That is, (1) It was calculated and compared whether the oxygen atom O of CO or the carbon atom C is on the Pt surface side has lower energy. As a result, it was confirmed that the arrangement of carbon atoms C on the Pt surface side shows a lower calculated energy value. Therefore, the arrangement of CO is determined so that the carbon atoms C are on the Pt surface side. (2) The CO molecules determined as in (1) are arranged at three locations with different distances from the model surface, and the position with the lowest energy calculation value among the three locations is the highest on the metal surface. It was fixed as a stable CO arrangement position.

  Thus, in the present embodiment, the first and second adsorption energies are calculated based on the CO arrangement (assuming adsorption) when the desired substituent atoms are arranged under the above conditions (1) and (2). did. Table 1 shows the calculation results of the first and second adsorption energies in each model in which one atom of the surface of the base material atom Pt1 is replaced with any one of Ir, Rh, Pd, Au, and Ag.

  As shown in Table 1, when the substitution atom 2 is Rh or Ir, the substitution shown in FIG. 1A is more effective than the case where CO is arranged on the Pt atom 1 immediately beside the substitution atom 2 shown in FIG. The CO adsorption energy (first adsorption energy) was lower when CO was arranged immediately above the atom 2 (Ir or Rh). The low first adsorption energy means that CO is likely to be adsorbed. When the substituent atom is Ir or Rh, CO is easily adsorbed to the substituent atom itself. Note that the first adsorption energy at this time was lower than the adsorption energy of CO in the case where a part of the base material atom Pt is not substituted with a substitution atom (in the case of only Pt).

  On the other hand, in the case where the substitution atom 2 is Pd, Au, or Ag, it is more directly adjacent to the substitution atom 2 as shown in FIG. 1B than when CO is arranged immediately above the substitution atom 2 in FIG. The CO adsorption energy (second adsorption energy) was lower when CO was disposed on the Pt atom 1. Therefore, when the substituted atom 2 is Pd, Au, or Ag, CO is not easily adsorbed on the substituted atom 2 itself, and the substitution of the substituted atom 2 results in CO being present on the surrounding Pt atom 1. It can be said that it plays an auxiliary role of facilitating adsorption. Note that the second adsorption energy at this time was lower than the adsorption energy of CO in the case where a part of the base material atom Pt is not substituted with a substitution atom (in the case of only Pt).

  In addition, it should be noted here that when the substitution atom is Pd, Au, or Ag, the first adsorption energy when CO is arranged immediately above the substitution atom is the CO on Pt without substitution. This is higher than the second adsorption energy and is in a state in which CO is hardly adsorbed. That is, when Pd, Au, and Ag are in a state of covering the material surface, it is assumed that the adsorption of CO becomes worse.

  From the results shown in Table 1, it is possible to classify Rh and Ir into the first group, which is a substituent in which the atoms themselves easily adsorb CO, and Au, Pd and Ag are difficult to adsorb CO. It can be classified into a second group that improves the adsorptivity at the horizontal Pt.

  Then, when producing the catalyst material, based on the classification result, the catalyst material is so substituted that a part of the base material atoms is replaced with a substitution atom belonging to the first group and a substitution atom belonging to the second group. Manufacturing.

  Here, the reason why a part of the base material atoms is replaced with a substitution atom belonging to the first group and a substitution atom belonging to the second group will be described.

  Atoms are selected one by one from both the first group (Ir, Rh) and the second group (Pd, Au, Ag), and in the crystal structure of the matrix atom Pt, the matrix atoms located on the surface are A simulation model in which atoms are substituted one by one with selected substitution atoms and the results of calculating the adsorption energy of CO will be described. 2A to 2C show simulation models at this time.

  In the simulation model shown in FIGS. 2A to 2C, for example, in the crystal structure of the base atom Pt arranged in a close-packed structure, Pt positioned on the surface whose crystal plane is the [111] plane is expressed as In this structure, the substitution atom Rh belonging to one group and the substitution atom Pd belonging to the second group are substituted.

  Using this simulation model, as shown in FIG. 2A, as a result of calculating the adsorption energy when CO is adsorbed on the substitution atom Rh belonging to the first group, it is −0.0284Ha, and FIG. As shown in b), the result of calculating the adsorption energy when CO is adsorbed on the base material atom Pt is -0.0221Ha, and as shown in FIG. 2C, CO belongs to the second group. As a result of calculating the adsorption energy when adsorbed on the substitution atom Pd, it was -0.0177Ha.

Then, the average value of the adsorption energy was calculated when the CO adsorption positions were the base material atom, the substituted atom belonging to the first group, and the substituted atom belonging to the second group. The results are shown in Table 2. Note that, as an average value, a simple average obtained by dividing the total value of adsorption energies at three adsorption positions by 3 and an average value based on a Boltzmann factor represented by probability: e ^{−E / kT} were calculated. Table 2 also shows, for reference, an average value when only Pt is substituted with one type of substituent atom.

  As shown in Table 2, when the base atom is Pt, the substitution atom belonging to the first group is Rh, and the substitution atom belonging to the second group is Ag (Pt + Rh + Ag in the table), the simple average value is −0. The average value based on the Boltzmann factor was -0.0290. These both average values are the average values of both Pt alone, or the case of substitution with only the substituted atoms belonging to either the first or second group, that is, the substitution with only Rh (Pt + Rh in the table). , It is found that it is lower than the average value in the case of substitution with Ag alone (Pt + Ag in the table).

  When the base atom is Pt, the substitution atom belonging to the first group is Rh, and the substitution atom belonging to the second group is Au (Pt + Rh + Au), the simple average value is −0.0194Ha, and the Boltzmann factor is The average value based on this is -0.0269, and these both average values exclude the simple average value in the case of only Pt, both average values in the case of only Pt, and both average values in the case of Pt + Rh and Pt + Au. It can be seen that it is low compared to.

  Similarly, when the base material atom is Pt, the substitution atom belonging to the first group is Rh, and the substitution atom belonging to the second group is Pd (Pt + Rh + Pd), the simple average value is −0.0227Ha, and the Boltzmann factor It can be seen that the average value based on is -0.0277, and both of these average values are lower when Pt + Rh than when only Pt is compared with the average value when Pt + Pd.

  In this way, one substitution atom is selected from each of the first group (Ir, Rh) and the second group (Pd, Au, Ag), and the parent located on the surface in the crystal structure of the base material atom Pt. By substituting a part of the material atoms one by one with the selected substitution atom, it is possible to replace a part of the matrix atom with only the substitution atom belonging to either the first group or the second group. Compared with the case of substitution, the CO adsorption energy can be lowered, and the catalyst material can be easily adsorbed on the surface of the catalyst material by configuring the catalyst material in this way.

  In general, the higher the gas adsorbability on the surface of the catalyst material, the more the chemical reaction of the gas is promoted. Therefore, according to the present embodiment, a part of the base material atoms is replaced with a replacement atom belonging to one group. Compared with the case where it was made to improve, the effect which accelerates | stimulates the chemical reaction of the gas of a catalyst material can be improved.

  Further, as can be seen from Table 2, when Pt + Rh + Ag, Pt + Rh + Au, and Pt + Rh + Pd, the average value based on the Boltzmann factor is lower than the simple average value. The following can be said from this.

  3A and 3B are schematic diagrams when CO is adsorbed on the surface of the catalyst material. FIG. 3A shows the case of the simple average value in Table 2, and FIG. 3B shows the case of the average value based on the Boltzmann factor in Table 2.

  When there is a region where the adsorption energy of CO is different on the surface of the catalyst material, that is, a region where CO is likely to be adsorbed and a region where CO is not likely to be adsorbed, as shown in FIG. Since a finite time is required even if it takes a short time from the adsorption of CO to the reaction / desorption, the CO that subsequently comes to the Pt / or Pt surface with the substituted atoms is easily adsorbed on the surface ( Since the hatched area 11 in the figure is occupied by the CO that has come first, it must be stopped and adsorbed to another position 12.

  On the other hand, in a low-concentration gas atmosphere, as shown in FIG. 3 (b), there are relatively many positions (shaded areas in the drawing) 11 that are likely to be adsorbed, or (if not many). The possibility of being occupied by the CO that has come first decreases, and the position 11 that is easily adsorbed easily exists. That is, CO is selectively adsorbed on the metal surface, and the selective adsorption becomes dominant, and since the amount of CO gas is small, it cannot be adsorbed to a highly adsorbing part due to inhibition of previously adsorbed CO. Negative factors are smaller.

  Therefore, the catalyst material in which a part of the base material atom is substituted by using the above-described bisected substituent atoms, such as Pt + Rh + Ag, Pt + Rh + Au, and Pt + Rh + Pd, for example, if the concentration becomes less than 1%. It can be said that it is effective.

In the above simulation, CO adsorption energy is calculated using CO. However, the adsorption energy of the gas may be calculated using another gas such as H ₂ instead of CO. Even in this case, the same effect can be obtained by selecting a substitute by the same procedure and finding a material having a low adsorption energy.

  Regarding the type of gas, for example, a gas component obtained from exhaust gas when an object such as an engine is driven is drawn into a bag, a part of the gas is taken out from the bag, and a measuring instrument such as gas chromatography is used. The main component gas is determined by examining the constituent gases. If the main component gas is arranged on the surface of the model and a material (substitution) having a low adsorption energy is found, a reaction promoting material more suitable for the purpose can be found.

For example, as a main component _{gas, CH 4, C 2 H 6} , C 3 H 8, C 3 H 6, CO, NO x, such as _{H 2} and the like. The above-mentioned main component gas is a rough example, the type of engine, and the difference in fuel in diesel cars other than the current gasoline cars, and further fuels used in the future, such as ethanol and biofuels, and driving conditions Needless to say, the main component changes depending on the method.

  In the present embodiment, as an example, a case where CO is the main component is assumed, and the calculation results using individual gases as models when assuming a gas other than CO as the main component will be described later. This is shown in the embodiment.

  In addition, it is suitable to use the adsorption energy as an index as described above, not only when the CO concentration is as high as 1%, but only in a region such as 200 ppm or less. The determination method in this region is that when the oxygen amount is changed between a state with a lot of oxygen (lean: L) and a state with a small amount of oxygen (rich: R), the reducing gas and oxygen are theoretically expressed in the chemical formula. In addition, it is judged whether or not the change in the remaining amount of gas in the region where the reaction is performed without lapse occurs instantaneously and can be followed.

  For example, in the oxygen sensor, the change in the residual gas appears as a sensor output according to the Nernst equation. In the region where the sensor output changes instantaneously, that is, the followability of the chemical reaction is good and the gas reaction reaches an equilibrium state, for example, the region where the CO concentration is 1%, the adsorption energy is obtained and compared, and the reaction promoting material Even if it is determined, no significant effect appears, and even the presence or absence of the effect is unknown.

  On the other hand, when the gas amount decreases, the change in sensor output is delayed. This is because the gas reaction has not reached an equilibrium state, which can be explained by the probability theory described below.

  If the probability of follow-up is shown by probability theory, the problem can be solved if the reaction probability is improved, and the adsorption probability can be improved as a method of improving the reaction probability. A material to be reduced may be used as a reaction promoting material.

  Here, FIG. 4 shows a model for explaining the reaction probability. In the model shown in FIG. 4, n oxygens are dispersed in N mesh cells. Here, it is assumed that up to two gases can enter the same cell, and oxygen does not enter the same cell. Also, in this model, there are (2N−n) vacant spaces, and there is no reaction when entering (2N−2n) locations.

  M reducing gases (for example, CO) are added here. Hereinafter, the reducing gas is indicated by CO.

At this time, the probability that the first CO does not react is (2N-2n) / (2N-n). Also, the probability that the reaction will not occur even if the second CO enters
(2N-2n) / (2N-n) × (2N-2n-1) / (2N-n-1).

  And the probability Pm that does not react even if m pieces of CO enter is as follows.

Pm = [(2N-2n)! / {2N- (2n + m)}! ] / [(2N-n)! / {2N- (n + m)}! ]
Here, if m = α × n for the convenience of transformation of the equation, Pm is as follows.

Pm = [(2N-2n)! / {2N- (2n + αn)}!
] / [(2N-n)! / {2N- (n + αn)}! ]
Here, Stirling's approximate expression (below) is applied.

If n is large, n! ≈ (2πn) ^0.5 × n ⁿ × e ⁻ⁿ

  Then, in order to simplify the equation, the logarithm (ln) of Pn is as follows.

lnPn = ln (2N-2n)! + Ln {2N- (1 + α) n}! -Ln (2N-n)! −ln {2N− (2 + α) n}!
Then, assuming that N is sufficiently large and applying the Stirling approximation, lnPn is as follows.

lnPn = 0.5ln (2N-2n) + (2N-2n) ln (2N-2n) + 0.5ln {2N- (1 + α) n} + {2N− (1 + α) n} ln {2N− (1 + α) n } -0.5ln (2N-n)-(2N-n) ln (2N-n) -0.5ln {2N- (2 + α) n}-{2N- (2 + α) n} ln {2N- (2 + α) n}
Next, for example, ln (2N-2n) = ln2N + ln (1-n / N) is decomposed and the following approximate expression is applied to the lnPn.

ln (1 + x) ≈x (when x is sufficiently smaller than 1)
lnPn = 0.5 ln (2N−2n) +0.5 ln {2N− (1 + α) n} −0.5 ln (2N−n) −0.5 ln {2N− (2 + α) n} −αn ² / N
lnPn = 0.5ln [(2N-2n) {2N- (1 + α) n}] − 0.5ln [(2N−n) {2N− (2 + α) n}] − αn ² / N
Here, in the first and second terms of the above equation, n is sufficiently smaller than N, so if the term n ² is ignored, there is no logarithmic term,
lnPn = −αn ² / N.
Pn in the following formula is the probability of not reacting even if αn pieces of CO enter, so
lnPn = −αn ² / N
Probability that at least one CO will react: P is
P = 1-Pn
= 1−EXP (−αn ² / N) (1)
It becomes.

  If the above probability that the reaction occurs at least once is proportional to the progress of the reaction, the above equation (1) should represent a non-equilibrium steady state when the followability of the reaction is poor.

  Here, FIG. 5 shows the relationship between the excess oxygen ratio λ and the sensor output when α is input in accordance with the value of λ in the above equation (1) and the sensor output is obtained. The vertical axis in FIG. 5 is arbitrary. When α is input in accordance with the value of λ and the sensor output is obtained, a graph shown in FIG. 5 is obtained, and the result is the same as the graph shown in FIG. 22 when CO is at a very low concentration. From this, it can be said that the delay in the change in the sensor output of the λ characteristic is due to the steady state of the non-equilibrium state.

  In such a case, by reducing the adsorption energy of the desired gas and improving the adsorption probability, the reaction can proceed more quickly, and as a result, the oxygen concentration is lowered and the delay in the change in the sensor output is improved. It leads to a thing (in FIG. 5, an arrow and a dotted line).

  In the above description, “200 ppm or less” describes the region in which the delay in the change in the sensor output of the λ characteristic has been experimentally confirmed, and the upper limit is not determined by a numerical value of 200. To the last, in the gas concentration region where a delay in the output of the sensor is confirmed, performance improvement due to a decrease in adsorption energy is effective, and this region is a region that needs to be improved with the recent clean-up of gas. That is, it is also new that the performance improvement due to a decrease in adsorption energy has become effective.

  In the first-principles calculation used in this simulation, the energy is calculated by forming and fixing the model, and the energy of the model is obtained and the gradient is used to move atoms and electrons in a more stable direction. There is a “structure optimization calculation” that is repeated many times. In the latter method, atoms are moved in a more stable direction, so there are cases where molecules are located instead of gas atoms directly above the substitution atoms or base atoms, so the atoms or molecules of the target gas are replaced. The first adsorption energy of the gas when arranged immediately above the atom, and the second adsorption energy of the gas when the atom or molecule of the target gas is arranged immediately above the base atom positioned next to the substitution atom Will be calculated.

  In the first embodiment, the former method is adopted, but other calculation methods such as the latter structure optimization calculation method with higher accuracy may be adopted. For reference, in the first embodiment, for CO, the energy calculation is performed individually by changing the arrangement of three points CO in the vertical direction from the surface of the Pt-based material, and atoms are fixed at the lowest energy among them.・ Comparison, but when this was confirmed and confirmed by the above structural optimization calculation, there was no significant difference in which the magnitude relationship of energy was switched.

  Next, the manufacturing method of the electrode for oxygen sensors performed based on the above simulation result is demonstrated.

  First, the structure of the sensor element used for the oxygen sensor will be described. The oxygen sensor is composed of a sensor element and a cylindrical housing into which the sensor element is inserted and fixed.

  6 is a top view of the sensor element 20, and FIG. 7 is a cross-sectional view taken along line AA in FIG. In addition, about structures other than the sensor element 20 of an oxygen sensor, since the structure similar to a general oxygen sensor is employable, description is abbreviate | omitted here.

  The sensor element 20 of the present embodiment is a laminated type similar to the gas sensor described in Patent Document 2, and as shown in FIGS. 6 and 7, a zirconia layer 22 as a solid electrolyte body having oxygen ion conductivity, As a surface electrode 25 as a measurement gas side electrode provided on the surface of the zirconia layer 22 facing the measurement gas, and as a reference gas side electrode provided on the surface of the zirconia layer 22 facing the reference gas , And a pair of lead portions each having one end connected to each electrode and the other end connected to a signal extraction terminal.

  More specifically, the sensor element 20 of the present embodiment has, for example, a laminated structure of an alumina layer 21 and a zirconia layer 22 as shown in FIG.

  The alumina layer 21 is provided with a recess 23 constituting an air duct as a reference gas chamber on the surface 21a on the zirconia layer side, and a heater 24 for heating the oxygen sensor 20 on the opposite back surface 21b side inside. Is installed.

  A surface electrode 25 is formed on the surface 22a of the zirconia layer 22 as shown in FIGS. 6 and 7. As shown in FIG. 6, a predetermined region 25a on one end side thereof (hereinafter referred to as a tip region 25a). Is made of, for example, a solid solution of Pt, Rh, and Ag, and the other region 25b is made of Pt.

  Further, as shown in FIGS. 6 and 7, a back electrode 26 is formed on the back surface 22 b of the zirconia layer 22 so as to face the air duct. The back electrode 26 is made of, for example, Pt. In FIG. 6, the relative position of the back electrode 26 with respect to the front surface 22 a of the zirconia layer 22 is indicated by a broken line. Further, for example, lead wires made of Pt are connected to the front electrode 25, the back electrode 26, and the heater 24. In addition, although not shown in the front end region 25a, a porous diffusion resistance layer for diffusing gas is provided so as to cover at least the surface electrode 25, and a gas shielding layer for shielding gas is further provided thereon. Provided.

  In the oxygen sensor having the sensor element 20 having such a configuration, a measurement gas to be measured is caused to flow through the porous diffusion resistance layer on the front electrode 25, and the atmosphere as a reference gas is caused to flow over the back electrode 26. The electromotive force generated by the difference in concentration between the target gas and the atmosphere is measured by a measuring instrument connected via a lead wire.

  Then, the manufacturing method of the oxygen sensor (sensor element 20) of an above-described structure is demonstrated. Hereinafter, a case where Rh is selected from the first group and Ag is selected from the second group will be described as an example. FIG. 8 shows a part of the manufacturing process of the sensor element 20. FIG. 8 is an enlarged view of a portion corresponding to the region B in FIG.

  In this embodiment, ceramic green sheets of alumina and zirconia containing a solvent, a binder, and the like are laminated. At this time, a Pt paste material is applied to a region where the back electrode 26 is to be formed (see FIGS. 6 and 7) in the back surface 22 b of the zirconia layer 22, and the surface electrode 25 is formed in the surface 22 a of the zirconia layer 22. In applying the Pt paste material to the planned region (see FIGS. 6 and 7), the Pt + Rh paste (Pt + first replacement material) is applied only to the tip region 25a, and the Pt paste material is applied to the other region 25b. The composition ratio of the Pt and Rh paste material is Pt: Rh = 80: 20.

  Thereafter, for example, by firing at 1450 ° C., the alumina layer 21 and the zirconia layer 22 are fixed, the back electrode 26 is formed, and further, Rh is dissolved in Pt in a region where the front electrode 25 is to be formed. A solid solution layer 31 is formed.

  Subsequently, as shown in FIG. 8, the Ag film is formed by vapor deposition on the entire region where the tip region 25 a is to be formed out of the surface of the solid solution layer 31 of Pt and Rh formed on the surface 22 a of the zirconia layer 22. (Second replacement material) 32 is formed. Thereafter, for example, baking is performed at 900 to 940 ° C. for 2 hours. Thereby, Ag can be further dissolved in Pt.

  In this way, for example, the surface electrode 25 made of Pt, Rh, and Ag and having a structure in which a part of Pt is substituted with Rh and Ag can be formed. Thereafter, for example, an oxygen sensor having the sensor element 20 can be manufactured by forming a porous diffusion resistance layer, a gas shielding layer, and the like by a general manufacturing method.

  Here, as a reference, in FIGS. 9A to 9D, when only Pt is used, when Rh is dissolved in Pt (PtRh), and when Ag is vapor-deposited (PtRh + Ag vapor deposition), On the other hand, the XRD measurement result when it heat-processes at 900 degreeC-2 hours (PtRh + Ag heat processing) is shown.

  FIG. 9A shows the XRD measurement result when the Pt paste is fired at 1450 ° C., and the peak position of Pt can be confirmed. FIG. 9B is an XRD measurement result when the Pt + Rh paste is fired at 1450 ° C., and the peak position is slightly shifted to the high angle side, so that it is understood that Rh is dissolved in Pt. .

  FIG. 9C shows the XRD measurement result in a state where the Ag film 32 is deposited on the surface of the solid solution layer 31 of Pt and Rh as shown in FIG. 8 (Ag film is not fired). When the Ag film is not fired, as shown in FIG. 9C, Pt, Rh, and Ag are the same crystal system and only have different lattice constants. Therefore, the number of peaks is the same and shifts according to the lattice constant. As a result, a new Ag peak appears.

  FIG. 9D shows the XRD measurement result after the Ag film 32 is deposited on the surface of the solid solution layer 31 of Pt and Rh and then heat treated at 900 ° C. for 2 hours. At this time, in FIG. 9D, a new peak was observed between the peak position of PtRh and the peak position of Ag, as can be seen in comparison with FIG. 9C. From this, it can be seen that Ag is further dissolved with respect to Pt in which Rh is dissolved. The XRD measurement results were the same when 900 ° C. was changed to 940 ° C.

  In the present embodiment, as described above, as a method for forming the surface electrode 25, a method of applying the Pt + Rh paste 31 to the surface 22 a of the zirconia layer 22 and baking it, forming the Ag film 32, and baking again. Is adopted (see FIG. 8).

  This is because Ag has a melting point of around 960 ° C. and melts at a temperature lower than the firing temperature of Pt and Rh (eg, 1450 ° C.), so that, for example, 1450 ° C. In order to avoid this, the Ag is evaporated and the surface electrode 25 is unlikely to have a desired configuration.

  That is, in the case where the second replacement material is a material that melts under the temperature condition for dissolving the base material and the first replacement material, in order to make the first and second replacement materials dissolve in the base material, When the co-firing, the second substitution material having a lower melting point is vaporized and may be drastically reduced from a desired amount.

  Therefore, in such a case, as in the present embodiment, the base material and the first replacement material containing a substitution atom belonging to one of the first and second groups are fired, and the first replacement material is applied to the base material. After the solid solution is formed, a second replacement material containing a substitution atom belonging to the other of the first and second groups is formed on the surface of the base material and baked, so that the second replacement material is dissolved in the base material. Thus, it is preferable that a part of the base material atoms is substituted with a substitution atom belonging to the first group and a substitution atom belonging to the second group. At this time, the first substitution material is baked at a temperature suitable for the first substitution material, and the second substitution material is baked at a temperature suitable for the second substitution material. The electrode 25, that is, the catalyst material can be formed.

  Further, as in the present embodiment, instead of firing both at the same time, the substitution atoms remaining after firing one are formed on the surface and dissolved, so that the solid atoms of the base material atom and the two substitution atoms are solidified. Priority is given to the solid solution of the easily soluble material atoms, and it can be prevented that the remaining atoms do not / are hardly dissolved, and it may be possible to give priority to the solid solution of a desired combination. . In addition to the above purpose, it is possible to distribute specific substitution atoms on the surface and increase the amount of distribution on the surface.

  In the present embodiment, it is further preferable to do the following. That is, when the film is formed and solid-solved after firing, for example, if the solid solution is formed by heat treatment, the solid solution is promoted by heat treatment at a temperature slightly lower than the melting point of the fired material or the deposited material. At this time, however, comparing the surface and its back, generally, the deposited material is distributed more on the surface than the fired material, and the fired material is more on the back than the deposited material. Often distributed. For this reason, the distribution ratio of components on the surface is not always optimal. Therefore, in order to adjust the distribution of Pt, Rh, and Ag components in the vicinity of the surface of the surface electrode 25, it is preferable to adjust the temperature and time by, for example, examining the distribution with respect to the firing temperature and firing time.

  As a matter of course, a plurality of materials of the second group may be included. For example, a method in which Ag is dissolved in advance with Pd having a higher melting point and other materials including Pt are simultaneously fired. You may take it. Further, the material to be dissolved in advance with Ag is not necessarily limited to a material belonging to the second group such as Pd, and may be a material belonging to the first group.

  In the present embodiment, as a method for manufacturing the oxygen sensor 20 (surface electrode 25), in consideration of the melting point of Ag being lower than the firing temperature of Pt and Rh, after applying and firing the Pt + Rh paste 31, The method of forming the Ag film 32 and firing again was employed, but instead of this method, a paste material containing Pt, Rh, and Ag was applied and fired at 1450 ° C., for example. A method of substituting a part of these with Rh and Ag may be adopted. In addition, when the present inventors actually applied a paste material containing Pt, Rh, and Ag and baked at 1450 ° C., it was confirmed that a surface electrode in which a part of Pt was substituted with Rh and Ag could be formed. Yes.

  Here, using three types of paste materials in which the composition ratio of Ag in the paste material containing Pt, Rh, and Ag is 4.9%, 9.5%, and 13.5% of the total composition, the paste material Was applied and baked to form a surface electrode in which a part of Pt was substituted with Rh and Ag, and the performance of the oxygen sensor was evaluated in the same manner as in the first embodiment. As a result, in the case of using a paste material with a composition ratio of Ag of 4.9%, the locus of the sensor output value when the oxygen excess ratio λ increases and when it decreases decreases greatly. In the graph showing the relationship between the λ value and the λ value, a hysteresis curve was drawn. On the other hand, when a paste material having an Ag composition ratio of 9.5% and 13.5% was used, the locus of the sensor output value was the same when the oxygen excess ratio λ increased and decreased.

  Therefore, when a method of forming a surface electrode in which a part of Pt is substituted with Rh and Ag by applying and baking a paste material containing Pt, Rh, and Ag, the paste material of Ag is used as the paste material. It is preferable to use a composition having a composition ratio larger than 4.9% of the total composition, and it is more preferable to use a composition ratio of 9.5% or more.

  Next, the performance of the oxygen sensor manufactured by the above method will be described.

  The performance of the oxygen sensor 20 manufactured by the manufacturing method of this embodiment was measured by the following method. That is, with reference to FIG. 7, a target gas is caused to flow on the electrode material (surface electrode 25) using a measurement jig (not shown), and the air duct 23 is completely separated from the target gas. Then, only the atmosphere was flowed, and the output (electromotive force) of the sensor generated at this time was measured.

Specifically, N ₂ gas is 2000 ml / min. In order to check for gas leakage and gas flow, it was confirmed for each measurement that the pressure increased to 1400 HPa. The gas was heated to 600 ° C. before flowing into the element, and the portion where the sample was set was heated to 500 ° C. Further, in order to remove the influence of the gas left in the pipe, the electric power of the heater 24 (see FIG. 7) was adjusted to leave the sensor element at 600 ° C. for 10 minutes. Then, the electromotive force when changing the amount of oxygen in the target gas was measured.

Here, the composition of the target gas was N ₂ , O ₂ and CO, or N ₂ , O ₂ and H ₂ . In either case, the total amount of gas was 2000 ml / min. When H ₂ was fixed at 100 ppm or 50 ppm and CO was fixed at 100 ppm or 200 ppm, oxygen was changed in accordance with the oxygen excess rate (λ), and the rest was adjusted with N ₂ . In addition, it measured similarly when the sensor temperature was 400 degreeC.

FIGS. 10 (a) and 10 (b) show the measurement results when CO is 200 ppm and the temperatures are 400 ° C. and 600 ° C., respectively, and FIGS. 11 (a) and 11 (b) show CO is 100 ppm. The measurement result when temperature is 400 degreeC and 600 degreeC is shown. 12A and 12B show the measurement results when H ₂ is 100 ppm and the temperatures are 400 ° C. and 600 ° C., respectively, and FIGS. 13A and 13B show H ₂ of 50 ppm. And the measurement results when the temperature is 400 ° C. and 600 ° C., respectively. In each figure, the oxygen excess rate λ is shown as a result of changing both from the R (rich) to the L (lean) side and from the L to the R side. The measurement results of a comparative example in which 25 is composed of only Pt are also shown. In the figure, R (rich) and L (lean) mean that the amount of CO or H ₂ is R (rich) or L (lean). Moreover, the results of FIGS. 10 to 13 are the results of measurement by changing the gas type and concentration without changing the installation environment of each sample. The surface electrode 25 is formed using a Pt + Rh + Ag paste material, and the composition ratio of the Pt + Rh + Ag paste material when the surface electrode 25 is composed of Pt, Rh, and Ag is PtRh (total of Pt and Rh) : Ag = 90: 10, Pt: Rh = 80: 20.

  As shown in FIGS. 10 to 13, in any case, it can be seen that the sensor output of the present embodiment (PtRhAg) shows a sharper change than the comparative example (Pt only). From this, it can be said that the catalyst material of the present embodiment has good acceleration of gas reaction, and particularly exhibits excellent effects as a sensor material.

  In addition, because of the steepness, the sensor output of the present embodiment (PtRhAg) is larger than that of the comparative example (only Pt) at the same λ value on the rich side. This is due to the fact that the gas reaction is promoted and the oxygen partial pressure is lowered, which indicates that it is also excellent as a reaction promoting material. In FIGS. 12A and 13B, it seems that such a result is not shown. This is because the right end on the lean side is divided by λ = 4, and when λ = 4. This is because the sensor output value is different between the present embodiment and the comparative example, that is, the result of the present embodiment is shifted downward in the figure.

  10 to 13 show the results under specific measurement conditions. Even with the same element, depending on the measurement conditions such as the size of the target gas inlet and the path to be attached to the jig used during Assy formation. The change point of sensor output (λ value indicating a steep change) only shifts, and the sensor output shows a steep change as described above even if the measurement conditions are different.

FIG. 14 shows the measurement results when this embodiment (PtRhAg), Comparative Example 1 (Pt only), and Comparative Example 2 (PtRh) are measured under the same conditions. The measurement conditions are H ₂ : 100 ppm and sensor temperature: 370 ° C. Comparative Example 2 is a measurement result when the tip region 25a of the surface electrode 25 is made of a material in which Rh is dissolved in Pt. Pt + Rh + Ag was produced by baking using a paste material of Pt: Rh = 80: 20, and forming and heat-treating Ag as described above.

  Furthermore, Table 3 shows the result of calculating the amount of change Δλ of the oxygen excess rate λ with respect to the change in the sensor output between 0.3 V and 0.6 V in the present embodiment and each comparative example from the measurement results of FIG. Show.

  As shown in Table 3, since Δλ is smaller in Comparative Example 2 than in Comparative Example 1, and Δλ is smaller in this embodiment than in Comparative Example 2, this embodiment has the largest change in sensor output. Is steep.

  Further, as shown in FIG. 14, in Comparative Example 2, the response of the sensor output value is different between when the λ value increases and when it decreases, that is, the relationship between the sensor output value and the λ value is In the graph shown, there is a problem of drawing a hysteresis curve.

  Here, in Table 4, in the measurement results of the present embodiment and the comparative example 2 in FIG. 14, a graph when changing from lean to rich (L → R) and a time when changing from rich to lean (R → L) ) And λ values of both graphs at the same sensor output value (4 points of 0.2V, 0.4V, 0.6V, and 0.8V) as an index indicating the breadth of the graph (difference in response). Shows the difference.

  Among the examples shown in Table 3, in Comparative Example 2 (PtRh electrode product) having a relatively small Δλ value and the present embodiment (PtRhAg electrode product) having the smallest Δλ value, the average values of the λ values shown in Table 4 are compared. Then, compared with Comparative Example 2, the present embodiment has a smaller difference in response of the sensor output value between when the λ value increases and when the λ value decreases, and it is on the rich side or the lean side. It is possible to feed back information in the same manner, that is, with a high degree of accuracy. Therefore, according to the present embodiment, efficient gas reaction can be promoted by accurate feedback of information.

  FIG. 15 shows the results of a performance confirmation test of the oxygen sensor having the sensor element 20 having the structure shown in FIGS.

  In FIG. 15, when the surface electrode 25 is made of Pt, it is made of Pt, Rh, and Ag (denoted as PtRhAg in the drawing), and it is made of Pt, Rh, and Pd (denoted as PtRhPd in the drawing). FIG. 3 shows a measurement result of λ characteristics (relationship between oxygen excess ratio λ and sensor output) when the target gas is CO. Further, the surface electrode 25 is formed of a paste material containing Pt, Rh, and Ag or a paste material containing Pt, Rh, and Pd. The composition ratio in this paste material is PtRh (total of Pt and Rh): Ag = 90: 10, Pt: Rh = 80: 20, or Pt: Rh: Pd = 80: 10: 10. The conditions at this time are 100 ppm for CO and 600 ° C., and other measurement conditions and specific measurement methods are the same as those in FIGS. FIG. 15 shows the results of performing sample preparation at the same time and measuring the λ characteristic of each sample on the same day in order to reduce measurement variations.

  Further, FIG. 16 shows the slope of the graph at λ = 0.5 in FIG. 15 for each sample (Pt, PtRhAg, PtRhPd) and the average value of CO adsorption energy in Table 2 (average value based on Boltzmann factor). The graph showing the relationship with) is shown.

  As shown in Table 2, the magnitude relationship between the average values based on the Boltzmann factor is PtRhAg (−0.0290), PtRhPd (−0.0277), and Pt (−0.0194) in descending order. , The slope of the graph at λ = 0.5 increases in the order of PtRhAg, PtRhPd, and Pt (PtRhAg is the steepest). As can be seen from the graph of FIG. The measurement result of 15 was the same as the calculation result of Table 2. From this, it can be said that the catalyst material manufactured by the method of this embodiment can exhibit an excellent effect as a sensor material.

17 and 18 show the results of another performance confirmation test of the oxygen sensor having the sensor element 20 having the structure shown in FIGS. 17 and 18, when the surface electrode 25 is composed of Pt and Rh (denoted as PtRh in the figure), and when it is composed of Pt, Rh and Ag (denoted as PtRhAg in the figure), the target gas It is a measurement result of the λ characteristic when H is H ₂ . Further, when the surface electrode 25 is formed using a paste material, and the surface electrode 25 is composed of Pt, Rh, and Ag, the composition ratio in the paste material is PtRh (total of Pt and Rh): Ag = 90 : 10, Pt: Rh = 80: 20. The composition ratio when the surface electrode 25 is composed of Pt and Rh is Pt: Rh = 80: 20. The conditions at this time are as follows: H ₂ concentration is 100 ppm in FIG. 17, H ₂ is 50 ppm in FIG. 18, and the temperature is 600 ° C. in FIGS. The measurement method is the same as in FIGS.

As shown in FIG. 17, in the case where the H ₂ concentration is 100 ppm, both PtRh and PtRhAg have a sharp change in sensor output, and by replacing a part of the crystal structure of Pt with Rh, It can be seen that the change in sensor output can be made steep.

On the other hand, as shown in FIG. 18, when the H ₂ concentration is 50 ppm, PtRh draws a hysteresis-like curve in the graph showing the relationship between the sensor output value and the λ value, and the λ value increases. And PtRhAg has a sharp change in the sensor output, and the λ value increases and decreases when the sensor output response decreases sharply. The output shows similar response behavior. For this reason, when the H ₂ concentration is as low as 50 ppm, when a part of the crystal structure of Pt is replaced with one kind of substituent atom Rh, the λ value increases and decreases. Since the difference in sensor output response is large, it is not possible to accurately feed back information. However, by replacing part of the crystal structure of Pt with both Rh and Ag, it decreases when the λ value increases. Since the difference in the response of the sensor output value from the time becomes small, it can be seen that information can be fed back with high accuracy. That is, it can be seen that the performance improvement by reducing the adsorption energy is effective in the gas concentration region where the output delay of the sensor is confirmed.

(Second Embodiment)
In the first embodiment, the simulation when CO is selected as the target gas to be adsorbed on the electrode of the gas sensor has been described. However, in the present embodiment, the simulation is performed by selecting H ₂ instead of CO. Will be described. In the present embodiment, differences from the first embodiment will be mainly described.

Similar to the first embodiment, a simulation model in which a part of a 16-solid Pt atom 1 having a close-packed structure is replaced with a desired substitution atom 2 (any one of Ir, Rh, Pd, Au, and Ag). using a first adsorption energy of H ₂ when placing of H ₂ directly above the replacement atom 2, of H ₂ when placing of H ₂ directly above the preform atoms located next to the substituted atom 2 The second adsorption energy was calculated. The results are shown in Table 5. As the calculation method, the structure optimization calculation described above was adopted.

As shown in Table 5, for the magnitude relationship of the first adsorption energy and the second adsorption energy of H ₂ at each substitution atoms 2, with the exception of Au, with similar results as in the first embodiment. That is, when the substitution atom 2 is Rh, Au, Ir, the first adsorption energy is smaller than the second adsorption energy. Therefore, Rh, Au, Ir can be classified into the first group, and the substitution atom 2 is Pd. , Ag, since the second adsorption energy is smaller than the first adsorption energy, Pd and Ag can be classified into the second group.

Accordingly, when the base material atom is Pt and Ir, Rh, Pd, Au, and Ag are selected as the substitution atoms and H ₂ is selected as the gas, among the substitution atoms, Rh, Au, Ir Are classified into the first group, Pd and Ag are classified into the second group, and a part of the crystal structure of Pt as a base material atom is divided into at least one atom of Rh, Au and Ir, and at least of Pd and Ag. Substitution with one atom is sufficient.

  Not only in the present embodiment, but can be said for all the calculated values, significant digits of each calculated value are 5 to 6 digits after the decimal point.

  However, for this project that aims at the synergistic effect by dividing the substitute into two, the difference between the calculated energy values of the first adsorption energy and the second adsorption energy has an average ratio of 10% or more for each calculated energy value. It is preferable. This is because if it is less than 10%, it is difficult to accurately recognize due to various factors even if the effect is less than 10%.

  If the difference in energy between the first adsorption energy and the second adsorption energy is 1% or 2% of each energy, Rh and Pd are less effective, but if Ag is 30% difference, then Rh and It is fully conceivable that the effect will appear even if combined. Due to the presence of Ag that is clearly difficult to adsorb, adsorption to Rh on a more limited surface is likely to occur, and reaction is likely to occur.

Here, the determination of whether or not the reaction is likely to occur includes the adsorption of oxygen molecules. On Pt, Rh, and Ir, two atoms in the oxygen molecule are adsorbed on the surface with almost no gap, so that the H ₂ is likely to react. On the Pd, Ag, and Au atoms, only one atom of the oxygen molecule is adsorbed on the surface, and the other atom is present in a large gap so that the shape of the oxygen atom is stable, so that the oxygen molecule is unlikely to diverge into two atoms. It depends on the calculation result that it is hard to react.

  In general, if there is a large difference in adsorption energy, the probability of occurrence is greatly different and the energy tends to be biased toward the lower energy, but if there is no large difference, it is easier to adsorb to the lower energy, but compared to the probability of occurrence. The big difference will disappear. Therefore, unlike Pd, the presence of Ag, for example, causes adsorption to Pt and Rh to be biased in both H2 and O2 to facilitate the reaction.

(Third embodiment)
In this embodiment, a case where CH ₄ is selected as the gas to be adsorbed and simulation is performed will be described. In the present embodiment, differences from the first embodiment will be mainly described.

Table 6, a first adsorption energy of CH ₄ when arranged CH ₄ immediately above the replacement atom 2, the CH ₄ when arranged CH ₄ just above the base material atoms located next to the substituted atom 2 The result of calculating the second adsorption energy is shown. As the calculation method, the structure optimization calculation described above was adopted.

As shown in Table 6, the magnitude relationship between the first adsorption energy and the second adsorption energy of CH ₄ for each substituent atom 2 was the same as that in the first embodiment. That is, when the substitution atom 2 is Rh, Ir, the first adsorption energy is smaller than the second adsorption energy, so that Rh, Ir can be classified into the first group, and the substitution atom 2 is Au, Pd, Ag. In this case, since the second adsorption energy is smaller than the first adsorption energy, Au, Pd, and Ag can be classified into the second group.

Therefore, when the base atom is Pt and Ir, Rh, Pd, Au, and Ag are selected as the substitution atoms and CH ₄ is selected as the gas, Rh and Ir among the substitution atoms are Classify into one group, classify Au, Pd, Ag into the second group, and part of the crystal structure of Pt as a base material atom, at least one of Rh and Ir, and at least one of Au, Pd, Ag What is necessary is just to substitute with an atom.

(Fourth embodiment)
In the present embodiment, a case where C ₂ H ₆ is selected as a gas to be adsorbed and a simulation is performed will be described. In the present embodiment, differences from the first embodiment will be mainly described.

Table 7, and the first adsorption energy of C ₂ H ₆ when arranged C ₂ H ₆ immediately above the replacement atom 2, the C ₂ H ₆ immediately above the base material atoms located next to the substituted atom 2 located shows a second result of calculating the adsorption energy of C ₂ H ₆ when the. As the calculation method, the structure optimization calculation described above was adopted.

As shown in Table 7, the magnitude relationship between the first adsorption energy and the second adsorption energy of C ₂ H ₆ for each substituent atom 2 was the same as in the first embodiment except for Pd. That is, when the substitution atom 2 is Rh, Ir, Pd, the first adsorption energy is smaller than the second adsorption energy. Therefore, Rh, Ir, Pd can be classified into the first group, and the substitution atom 2 is Au , Ag, the second adsorption energy is smaller than the first adsorption energy, so Au and Ag can be classified into the second group.

Therefore, when the base atom is Pt and Ir, Rh, Pd, Au, Ag is selected as the substitution atom and C ₂ H ₆ is selected as the gas, among the substitution atoms, Rh, Ir , Pd is classified into the first group, Au and Ag are classified into the second group, and a part of the crystal structure of Pt as a base material atom is combined with at least one atom of Rh, Ir, Pd, Au, Ag Substituting with at least one atom of

(Fifth embodiment)
In this embodiment, a case where C ₃ H ₈ is selected as a gas to be adsorbed and a simulation is performed will be described. In the present embodiment, differences from the first embodiment will be mainly described.

Table 8, a first adsorption energy of C ₃ H ₈ when placing the C ₃ H ₈ immediately above the replacement atom 2, the C ₃ H ₈ immediately above the base material atoms located next to the substituted atom 2 located It shows the the second result of calculating the adsorption energy of C ₃ H ₈ when. As the calculation method, the structure optimization calculation described above was adopted.

As shown in Table 8, the magnitude relationship between the first adsorption energy and the second adsorption energy of C ₃ H ₈ for each substituent atom 2 was the same as in the first embodiment except for Ag. That is, when the substitution atom 2 is Rh, Ir, Ag, the first adsorption energy is smaller than the second adsorption energy. Therefore, Rh, Ir, Ag can be classified into the first group, and the substitution atom 2 is Au , Pd, since the second adsorption energy is smaller than the first adsorption energy, Au and Pd can be classified into the second group.

Therefore, when the base material atom is Pt and Ir, Rh, Pd, Au, Ag is selected as the substitution atom, and C ₃ H ₈ is selected as the gas, among the substitution atoms, Rh, Ir , Ag is classified into the first group, Au and Pd are classified into the second group, a part of the crystal structure of Pt as a base material atom is combined with at least one atom of Rh, Ir, and Ag, Au, Pd Substituting with at least one atom of

(Sixth embodiment)
In this embodiment, a case where C ₃ H ₆ is selected as a gas to be adsorbed and a simulation is performed will be described. In the present embodiment, differences from the first embodiment will be mainly described.

Table 9, a first adsorption energy of C ₃ H ₆ when placing the C ₃ H ₆ immediately above the replacement atom 2, the C ₃ H ₆ immediately above the base material atoms located next to the substituted atom 2 located It shows the the second result of calculating the adsorption energy of C ₃ H ₆ when. As the calculation method, the structure optimization calculation described above was adopted.

As shown in Table 9, the magnitude relationship between the first adsorption energy and the second adsorption energy of C ₃ H ₆ for each substituent atom 2 was the same as in the first embodiment. That is, when the substitution atom 2 is Rh, Ir, the first adsorption energy is smaller than the second adsorption energy, so that Rh, Ir can be classified into the first group, and the substitution atom 2 is Pd, Au, Ag. In this case, since the second adsorption energy is smaller than the first adsorption energy, Pd, Au, and Ag can be classified into the second group.

Therefore, when the base material atom is Pt and Ir, Rh, Pd, Au, Ag is selected as the substitution atom and C ₃ H ₆ is selected as the gas, among the substitution atoms, Rh, Ir Are classified into the first group, Pd, Au, Ag are classified into the second group, and a part of the crystal structure of Pt as a base material atom is combined with at least one atom of Rh, Ir, Pd, Au, Ag. The at least one atom may be substituted.

(Other embodiments)
(1) FIG. 19 shows a part of the manufacturing process of the oxygen sensor 20 in another embodiment of the present invention. 19 is a top view of the oxygen sensor 20 corresponding to FIG. 6, and the same components as those in FIG. 6 are denoted by the same reference numerals as those in FIG.

  In the first embodiment, as a method for manufacturing the oxygen sensor 20, after the solid solution layer 31 of Pt and Rh is formed on the surface 22 a of the zirconia layer 22, the tip region 25 a is scheduled to be formed in the surface of the solid solution layer 31. The method of forming and baking the Ag film 32 over the entire region has been described as an example. However, when the Ag film 32 is formed, the solid solution layer 31 is not the entire region where the tip region 25a is to be formed. The Ag film 32 may be formed by covering a part of the surface with a mask.

  Specifically, as shown in FIG. 19, in the region where the tip region 25a is to be formed, the region where the Ag film 32 is formed and the region where the solid solution layer 31 is exposed alternately in the longitudinal direction of the surface electrode. An Ag film 32 is partially formed on the surface of the solid solution layer 31 so as to be positioned.

  Here, the base material and the substitution atom belonging to the first group facilitate gas adsorption immediately above it and promote the gas reaction, while the substitution atom belonging to the second group promotes adsorption to the side base material atom. In other words, it only plays an auxiliary role, and the substituted atoms themselves do not improve the gas adsorption and reaction promoting effects. Therefore, if the configuration / form is such that the surface of the material is covered with the substituent atoms belonging to the second group, the reaction promoting effect is reduced.

  Therefore, as in the present embodiment, when the substitution atoms belonging to the second group are formed on the surface and solid-dissolved, the film formation region is limited by masking in advance before the film formation and the second material is used as the base material. When the replacement material is dissolved, the second replacement material is diffused not only in the solid solution / diffusion in the depth direction from the surface, but also in the region covered with the mask material. It is possible to prevent the surface from being covered only with the material of the second group by dissolving / diffusing in the vicinity of the surface including the surface (diffusing in the direction along the surface). As a result, it is possible to suppress a decrease in the reaction promoting effect.

  (2) In each of the embodiments described above, as a method for manufacturing the oxygen sensor 20, after forming the solid solution layer 31 of Pt and Rh on the surface 22 a of the zirconia layer 22, Ag is formed on the surface of the solid solution layer 31. Although the method of forming the film 32 and baking it has been described as an example, it is preferable to add the following steps thereafter.

  That is, after solid solution of Rh as the first substitution material and Ag as the second substitution material in the matrix material Pt, in order to adjust the component ratio in the vicinity of the surface of the matrix material, It is preferable to perform the step of cutting the surface of the base material so that the base material or the first replacement material is partially exposed on the surface of the base material. At this time, the component distribution when the solid solution is dissolved under specific heat treatment conditions is examined in advance to scrape to a position where a desired distribution is obtained. As a method for scraping the surface, for example, etching can be employed.

  Thereby, it is possible to prevent the material surface from being covered with the substitution atoms belonging to the second group, and the substitution atoms belonging to the first group and the substitution atoms belonging to the second group near the surface of the base material. The composition ratio can be adjusted.

  In addition, about the method of adding the process of grinding this surface, you may implement instead of above-mentioned other embodiment (1), and may implement together.

  (3) In the first embodiment, when the tip region 25a of the surface electrode 25 is composed of a solid solution of Pt, Rh, and Ag, that is, Pt is used as a base material atom, Rh is selected from the first group, Although the case where Ag is selected from two groups has been described as an example, the combination of atoms selected from the first group (Ir, Rh) and atoms selected from the second group (Pd, Au, Ag) is changed to It is also possible to change the configuration of the region 25a. The same applies to the following embodiments.

  For example, when the tip region 25a is composed of a solid solution of Pt, Rh, and Pd, that is, when Rh is selected from the first group and Pd is selected from the second group, firing is performed simultaneously, Thus, Rh and Pd can be dissolved. That is, by laminating alumina and zirconia ceramic green sheets, instead of applying a paste material containing Pt and Rh to the region where the front electrode 25 is to be formed in the back surface 22b of the zirconia layer 22, Pt, Rh and Pd are applied. After applying the paste material (Pt + Rh + Pd paste) to be included, for example, by baking at 1450 ° C., Rh and Pd can be dissolved in Pt.

  (4) In each of the embodiments described above, the case where Pt is adopted as the base material atom and Ir, Rh, Pd, Au, Ag is adopted as the substitution atom has been described as an example. Atoms other than these may be employed as the substituent atoms. Moreover, you may employ | adopt the atom which functions as catalysts other than Pt as a base material atom. For example, Cu can be adopted as the base material atom. At this time, substitution atoms corresponding to the base material atoms are employed.

  It should be noted that, as a criterion for selecting the base material atom and the substitution atom, it is a condition that the substitution atom can be replaced with a part of the base material atom without breaking the crystal structure of the base material atom. For example, the relationship between the substitution atom and the base material atom is preferably a completely solid solution phase equilibrium diagram with substantially the same crystal structure. This is because the crystal structure is not broken at this time and there is no melting at a low temperature.

  In addition, for example, even if the substitute and the base material do not have a completely solid solution phase equilibrium diagram, the base material and the substitute do not melt at the operating temperature of the target product due to eutectic, etc. Any solid solution may be used. As described above, “the crystal structure is not broken” described here means that the crystal systems (for example, face-centered cubic lattices) are the same, the lattice constants may be different, and a part of the atoms are arranged. Distortion may occur. The meaning of substantially the same crystal structure is also the same.

  For example, as shown in the normal phase equilibrium diagram, not only the influence of material particles but also the reaction as a specially formed material, as represented by vapor deposition, sputtering, nanomaterial, mechanical alloying, etc. It may be made to do. At this time, there is no restriction on whether the classification of the crystal systems is the same.

  An example of a material that satisfies the above-described condition is that an atom forming a crystal structure of the same classification (for example, a face-centered cubic lattice) as that of the base material is used as a substitute. Further, the crystal structure of the same classification as the crystal structure of the base material need not be formed at room temperature. Since the purpose is to make a solid solution without breaking the crystal structure of the base material, it is sufficient that the crystal structure is substantially the same when the solid solution is formed. Here, “substantially identical” means that the crystal structures are the same and the lattice constants are different.

  (5) FIG. 20 shows a partial cross-sectional view of the cup-shaped sensor element 20, and FIG. 21 shows an enlarged view of the tip 201 in FIG. 20 and 21, the same components as those in FIGS. 6 and 7 are denoted by the same reference numerals as those in FIGS.

  In each of the above-described embodiments, the method of manufacturing the laminated sensor element 20 has been described. However, as shown in FIG. 20, for example, a bottomed cylinder having one end opened and the other end sealed. The present invention can also be applied to the manufacturing method of the cup-type sensor element 20.

  A sensor element 20 shown in FIG. 20 has the same configuration as the gas sensor described in Patent Document 3, and as shown in FIG. 21, a cup-type solid electrolyte body 22 having an air chamber 23 provided therein, and the solid electrolyte A measured gas side electrode 25 provided on the surface of the body 22 facing the measured gas (outside the solid electrolyte body), and a protective layer 27 made of a porous material provided outside the measured gas side electrode 25; The solid electrolyte body 22 includes a reference gas side electrode 26 provided on a surface facing the reference gas in the atmospheric chamber 23. As the solid electrolyte body 22, for example, zirconia is used as in the first embodiment. Further, a rod-shaped heater 24 that generates heat when energized is inserted and disposed in the atmospheric chamber 23 of the sensor element 20.

  The sensor element 20 having such a structure is manufactured as follows, for example.

  The solid electrolyte body 22 is formed into a cup shape and then baked to form the cup type solid electrolyte body 22. Next, in the same manner as the method for forming the surface electrode 25 described in the first embodiment, a paste material containing Pt and Rh is applied to the outer surface of the solid electrolyte body 22 and baked, so that a solid solution of Pt and Rh is obtained. Form a layer. At this time, the reference gas side electrode 26 is formed by applying a Pt paste material to the inner surface of the solid electrolyte body 22 and baking it. The reference gas side electrode 26 can also be formed by other methods such as chemical plating.

  Thereafter, a measurement gas having a configuration in which a part of the crystal structure of Pt is substituted with Rh and Ag on the outer surface of the solid electrolyte body 22 by forming an Ag film on the surface of the solid solution layer and firing it. The side electrode 25 is formed. Next, the protective layer 27 is formed on the surface of the measurement gas side electrode 25. The cup-type sensor element 20 is manufactured through these processes and the like.

  In addition, as a method of forming the gas-to-be-measured electrode 25, a method of applying a Pt + Rh paste and baking it, forming an Ag film, and baking again as in the other embodiment (3) described above. Instead of this, a method in which a part of Pt is substituted with Rh and Ag by applying a paste material containing Pt, Rh, and Ag and baking it may be employed.

  (6) In each of the above-described embodiments, the electrode 25 is formed by applying a paste material and firing the paste material. However, a part of the crystal structure of the base material atom can be replaced with another atom. If it is a method, you may employ | adopt other methods, such as an alloy plating method.

(7) In the first to sixth embodiments, the case where the gas to be adsorbed is individually selected and simulation is performed, the raw material is prepared based on the result, and the catalyst material is manufactured has been described. In order to obtain an effect of promoting a chemical reaction with respect to a plurality of gas components contained in a gas to be measured such as exhaust gas when an object such as an engine is driven, it is common to the plurality of gas components. It is preferable to select a substituent atom from each of the atoms belonging to the first group and the atoms belonging to the second group. For example, in order to obtain an effect of promoting a chemical reaction with respect to both CO and C ₂ H ₆ , as described in the first and fourth embodiments, it is common to both CO and C ₂ H _6. As a substituted atom to be classified, Rh is selected from the first group, Ag is selected from the second group, and a part of the crystal structure of Pt may be substituted with these atoms.

  In this way, in each of the main gases, excluding the gas whose content in the gas to be measured is extremely small, the first group that is a stable substitute in which the gas is adsorbed on the substitute In this case, the gas is adsorbed on the Pt beside the substitute and classified into the second group which is a stable substitute. Based on the classification result, the substitute is selected from the first and second groups. If there is a combination of the first and second groups common to all the main components contained in the gas to be measured, a replacement of that combination may be selected.

However, if there are too many main components contained in the gas to be measured and the combination of the first and second groups common to all is impossible, other than H _{2, which} tends to diffuse, As for the gas component, a substitute for Pt should be determined by giving priority to a combination in a gas that is difficult to adsorb, that is, a gas having a large adsorption energy.

This is because a gas that is difficult to adsorb is likely to have a poor follow-up performance of the sensor output, and therefore priority is given to preventing it. The reason why H ₂ is treated separately is that it is the gas that reacts most easily because the diffusion rate is large even if the adsorption energy is large. In addition, about the priority at the time of the said substitution material selection, preferentially handling gas with a gas amount extremely small deviates from the said concept.

(8) In each of the above-described embodiments, the oxygen sensor has been described as an example of the use of the catalyst material. For example, an A / F (air-fuel ratio) sensor that detects the oxygen concentration in the exhaust gas, and the NOx concentration are detected. The present invention can also be applied to an electrode of a gas sensor such as a NOx sensor that detects CO concentration, a CO sensor that detects CO concentration, a hydrogen sensor that detects H ₂ concentration, an ammonia sensor that detects NH ₃ concentration, and a manufacturing method thereof.

  That is, when manufacturing various gas sensor electrodes, the gas to be adsorbed on the gas sensor electrode is simulated using a simulation model in which a part of the base atom is replaced with a substitute atom for the crystal structure of the base atom. The first adsorption energy of the gas when the atom of the gas is arranged immediately above the substitution atom, and the first adsorption energy of the gas when the atom of the gas is arranged immediately above the base atom adjacent to the substitution atom 2. A simulation for calculating the adsorption energy is performed. Thereafter, as in the above-described embodiment, the raw material is prepared based on the simulation result, and the electrode of the gas sensor may be manufactured.

  In short, the present invention can be applied to all materials of a portion having a catalytic function.

  (9) In the first embodiment, using the simulation model, the first adsorption energy of CO when CO is arranged immediately above the substitution atom, and the CO is arranged immediately above the base material atom located next to the substitution atom. As a result of calculating the second adsorption energy of CO at the time, when the substitution atom 2 is Rh, Ir, the first adsorption energy is lower than the second adsorption energy, and the first adsorption energy at this time is It is lower than the adsorption energy of CO in the case where a part of the base atom Pt is not substituted with a substitution atom (in the case of only Pt), and in the case where the substitution atom is Pd, Au, or Ag, 2 The adsorption energy was lower and the second adsorption energy was lower than the adsorption energy in the case of only the base material atoms.

  Therefore, for CO, the first adsorption energy and the second adsorption energy calculated are compared, and the first adsorption energy is lower and the first adsorption energy is only the base material atom. Substitution atoms lower than the adsorption energy are classified into the first group, the second adsorption energy is lower than the first adsorption energy, and the second adsorption energy is higher than the adsorption energy in the case of only the base material atoms. It was described that lower substitution atoms are classified into the second group, and at least one substitution product is selected from each of the first group and the second group.

  However, the calculated second adsorption energy may not be lower than the adsorption energy in the case of only the base material atoms for the following reason.

  For the substituted atoms belonging to the first group, it has a direct influence on whether or not the gas is easily adsorbed. Therefore, it is necessary to improve the adsorptivity to be lower than the adsorption energy of the gas in the case of only the base material atoms, As described above, the substituted atoms belonging to the second group play an auxiliary role in the gas adsorption and enhance the adsorptivity of surrounding atoms. Therefore, at least one of the first group and the second group is used. It is only necessary to improve the adsorptivity when selecting and replacing each substitute. That is, when comparing the two energies, it is not always necessary that the second adsorption energy is lower than the adsorption energy in the case of only the base material atoms.

  Although it is preferable that the second adsorption energy is lower than the adsorption energy in the case of only the base material atoms, it is not always necessary when there are a plurality of gases. Furthermore, even if there are not a plurality of gases, it is only necessary to improve the adsorptivity when selecting and replacing at least one substitute from each of the first group and the second group.

It is a simulation model used by the first principle calculation in 1st Embodiment of this invention. It is a simulation model used by the first principle calculation in 1st Embodiment of this invention. It is a schematic diagram when CO adsorb | sucks to the catalyst material surface. It is a figure which shows a model when calculating | requiring the reaction probability for demonstrating that the followability of the change of a sensor output is bad by a probability theory. It is a figure which shows qualitatively the relationship between oxygen excess rate (lambda) and sensor output value when (alpha) is input into numerical formula (1) according to the value of (lambda), and a sensor output is calculated | required. It is a top view of the oxygen sensor in a 1st embodiment of the present invention. It is the sectional view on the AA line in FIG. 6 is a cross-sectional view of the oxygen sensor showing a part of the manufacturing process of the oxygen sensor 20. FIG. It is a figure which shows the XRD measurement result of the electrode material etc. which were manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. 15 represents the relationship between the slope of the graph at λ = 0.5 in FIG. 15 and the average value of CO adsorption energy in Table 2 (average value based on Boltzmann factor) for each sample (Pt, PtRhAg, PtRhPd). FIG. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a performance measurement result of the oxygen sensor 20 manufactured with the manufacturing method in 1st Embodiment of this invention. It is a top view of the oxygen sensor which shows a part of manufacturing process in other embodiments of the present invention. It is a fragmentary sectional view of sensor element 20 of an oxygen sensor in other embodiments of the present invention. It is an enlarged view of the front-end | tip part 201 in FIG. It is a figure which shows the relationship between oxygen excess rate (lambda) and sensor output value when Pt is used as an electrode of the sensor which has a catalyst function.

Explanation of symbols

1 ... base material atom, 2 ... substituent atom,
DESCRIPTION OF SYMBOLS 20 ... Oxygen sensor, 21 ... Alumina layer, 22 ... Zirconia layer, 23 ... Recess (atmosphere duct), 24 ... Heater, 25 ... Front electrode, 26 ... Back electrode,
31 ... Solid solution layer of Pt and Rh, 32 ... Ag film.

Claims (9)

A catalyst for a gas sensor having a structure in which a part of the base material atoms is replaced with a plurality of substitution atoms while maintaining the crystal structure of the base material atoms constituting the base material, and has an effect of promoting a gas chemical reaction. A method of manufacturing a material,
As a substitution atom, an atom that can be substituted for a part of the base atom without breaking the crystal structure of the base atom is selected, and a part of the base atom is substituted for the crystal structure of the base atom. Create a simulation model substituted with the substituted atoms,
Using the simulation model, the first adsorption energy of the gas when the target gas atom or molecule is arranged immediately above the substitution atom, and the target gas atom or molecule next to the substitution atom Calculating the second adsorption energy of the gas when arranged immediately above the base material atom located,
The calculated first adsorption energy and the second adsorption energy are compared, and the first adsorption energy is lower and the first adsorption energy is only the base material atom. Classifying substituent atoms lower than energy into the first group, and classifying substituent atoms with lower second adsorption energy than the first adsorption energy into the second group;
Based on the classification result, each of the substituted atoms belonging to the first group and the second group is selected, and a part of the base material atoms is part of the first group with respect to the crystal structure of the base material atoms. A method for producing a catalyst material, comprising producing the catalyst material by substitution with a substituted atom belonging to and a substituted atom belonging to the second group. In the case where the base atom is Pt and Ir, Rh, Pd, Au, Ag is selected as the substitution atom, and CO is selected as the gas, Rh and Ir are selected from the substitution atoms. Classify into the first group, classify Ag, Au and Pd into the second group;
The part of the crystal structure of Pt as the base material atom is replaced with at least one atom of Rh and Ir and at least one atom of Ag, Au, and Pd. A method for producing the catalyst material.   After firing the base material and a first replacement material containing a substitution atom belonging to one of the first and second groups, and dissolving the first replacement material in the base material, Forming a second substitution material containing a substitution atom belonging to the other of the first and second groups, baking the second substitution material to form a solid solution of the second substitution material in the matrix, 3. The method for producing a catalyst material according to claim 1, wherein a part thereof is substituted with a substitution atom belonging to the first group and a substitution atom belonging to the second group.   After firing the base material and a first substitution material containing a substitution atom belonging to the first group, and dissolving the first substitution material in the base material, the second group is formed on the base material surface. Forming a second substitution material containing a substitution atom belonging to, and baking the second substitution material to form a solid solution with the second substitution material in the matrix, so that a part of the matrix atoms is brought into the first group. The method for producing a catalyst material according to claim 3, wherein substitution is performed with a substituted atom belonging to and a substituted atom belonging to the second group.   The material composed of Pt is used as the base material, a material containing at least one of Rh and Ir is used as the first replacement material, and a material containing Ag is used as the second replacement material. 5. A method for producing a catalyst material according to 4.   When forming the second replacement material on the surface of the base material, the second replacement material is formed on the surface of the base material by forming a film while covering a part of the surface of the base material with a mask material. 6. The method for producing a catalyst material according to claim 4, wherein the film is partially formed.   In order to adjust the component ratio in the vicinity of the surface of the base material after the second replacement material is dissolved in the base material, the base material or the base material on the surface of the base material after the solid solution The method for producing a catalyst material according to any one of claims 4 to 6, wherein the surface of the base material is shaved so that the first replacement material is partially exposed.   A method for producing an electrode for a gas sensor, comprising producing an electrode for a gas sensor using the catalyst material produced by the method for producing a catalyst material according to any one of claims 1 to 7. Of the solid electrolyte body (22) having ionic conductivity, the measured gas side electrode (25) provided on the surface of the solid electrolyte body facing the measured gas, and the solid electrolyte body, In a method for manufacturing a gas sensor comprising a reference gas side electrode (26) provided on a surface facing a reference gas,
A method for manufacturing a gas sensor, wherein the measured gas side electrode (25) is formed using a catalyst material manufactured by the method for manufacturing a catalyst material according to any one of claims 1 to 7.

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