CN108360017B

CN108360017B - Catalyst for electrochemically reducing carbon dioxide into formic acid and preparation method thereof

Info

Publication number: CN108360017B
Application number: CN201810218911.XA
Authority: CN
Inventors: 赵鹏鹃; 张红飞; 康鹏
Original assignee: Carbon Energy Technology Beijing Co ltd
Current assignee: Carbon Energy Technology Beijing Co ltd
Priority date: 2018-03-16
Filing date: 2018-03-16
Publication date: 2020-04-07
Anticipated expiration: 2038-03-16
Also published as: CN108360017A

Abstract

Provides a catalyst for electrochemically reducing carbon dioxide into formic acid, wherein the catalyst is carbon-supported nano Zn_xSn_yO_zWherein 0 is<x<1，0<y<1, x + y is 1. Also provides a preparation method of the catalyst. According to the tin-zinc bimetallic composite catalyst, the two components generate a certain synergistic effect, so that high catalytic activity and selectivity of the catalyst are maintained, and good long-term stability can be maintained. In the preparation method of the zinc-tin composite catalyst provided by the invention, the proportion of zinc and tin can be freely adjusted, the particle size of the active component of the prepared catalyst reaches the nanometer level, and the catalyst is ensured to have more active sites and higher current density.

Description

Catalyst for electrochemically reducing carbon dioxide into formic acid and preparation method thereof

Technical Field

The invention relates to the field of electrochemical reduction, in particular to a catalyst for electrochemically reducing carbon dioxide into formic acid and a preparation method thereof.

Background

At present, the great emission of carbon dioxide on the earth and the adverse effect thereof on climate change attract extensive attention, and the reduction of the emission of carbon dioxide in the air becomes a problem to be solved urgently in human society. One scheme for reducing the emission of the carbon dioxide is to convert the carbon dioxide into products such as formic acid and the like by an electrochemical method, which is also an important way for realizing the resource recycling of the carbon dioxide.

One of the problems in the prior art of preparing formic acid by electrically reducing carbon dioxide is to develop a catalyst with high performance, high selectivity and high stability. The products of the electroreduction of carbon dioxide are not single but mixtures of components, e.g. CO, HCOOH, CH₃OH、CH₄And the like. Electrochemical reduction of carbon dioxide with Sn and Sn-based catalystsThe original formic acid has higher catalytic activity and selectivity. For example, the tin dioxide nano-structure catalyst is prepared in the patent No. CN103715436A, so that the specific surface area of the catalyst is improved, the electrochemical catalytic activity of the catalyst is increased, the hydrogen evolution reaction is effectively inhibited, and the selectivity of the product formic acid is enhanced. However, the tin dioxide nano catalyst has poor stability and is not corrosion-resistant, and cannot meet the requirement of long-term use.

The Zn nano-catalyst has better long-term stability for the electro-reduction of carbon dioxide to formic acid, but the catalytic activity is not ideal, and the selectivity of the Zn nano-catalyst to formic acid is not high, so that related researches on the electrochemical reduction of carbon dioxide by the Zn catalyst are not abundant so far. Shoichiro lkeda et al [ S.Ikeda, T.TakSni, K.Ito, Bull.Chem.Soc.Jpn.1987,60,2517-2522] prepared a Zn catalyst which reduced carbon dioxide to carbon monoxide in an aqueous solution containing tetraethylammonium perchlorate with the presence of other carbon dioxide reduction by-products, but no formation of formic acid was reported.

Disclosure of Invention

The invention provides a catalyst for electrochemically reducing carbon dioxide into formic acid and a preparation method thereof.

The invention provides a catalyst for electrochemically reducing carbon dioxide into formic acid, and the catalyst is carbon-supported nano Zn_xSn_yO_zWherein 0 is<x<1，0<y<1，x+y＝1。

According to one embodiment of the present invention, x/y ≧ 1.

According to another embodiment of the invention, the nano-Zn_xSn_yO_zThe grain size of (A) is 20-30 nm.

According to another embodiment of the invention, the carbon content of the catalyst is 50% and less of the total mass of the catalyst.

Another aspect of the present invention provides a method for preparing a catalyst for electrochemically reducing carbon dioxide to formic acid, comprising the steps of: s1: weighing a soluble zinc source compound and a soluble tin source compound according to a molar ratio, and dissolving the zinc source compound and the tin source compound in deionized water to prepare a precursor solution; s2: adding a carbon load into the precursor solution, and uniformly dispersing; and S3: preparing a strong base solution, adding the strong base solution into the carbon carrier/precursor solution, filtering after the reaction is finished, separating solid particles, washing, drying, grinding, and finally roasting to obtain the catalyst.

According to an embodiment of the present invention, the carbon support is one or more of carbon black, acetylene black, ketjen black, carbon nanofibers, and carbon nanotubes.

According to the tin-zinc bimetallic composite catalyst, the two components generate a certain synergistic effect, so that high catalytic activity and selectivity of the catalyst are maintained, and good long-term stability can be maintained. In the preparation method of the zinc-tin composite catalyst provided by the invention, the proportion of zinc and tin can be freely adjusted, the particle size of the active component of the prepared catalyst reaches the nanometer level, and the catalyst is ensured to have more active sites and higher current density.

Drawings

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

FIG. 1 is catalyst Zn prepared in example 1_0.9Sn_0.1O_zAn X-ray diffraction pattern of/C;

FIG. 2 is catalyst Zn prepared in example 1_0.9Sn_0.1O_zC and SnO₂The polarization curve of the/C catalyst at a voltage of 2.6V;

FIG. 3 is catalyst Zn prepared in example 1_0.9Sn_0.1O_zC and SnO₂A current efficiency histogram of the/C catalyst at different potentials;

FIG. 4 shows a zinc-tin composite catalyst and SnO prepared in comparative example 1₂A formic acid current efficiency change curve chart of a 24-hour continuous test of the/C catalyst; and

FIG. 5 is a bar graph of formic acid current efficiencies at a potential of 2.6V for the zinc-tin composite catalyst and the ZnO/C catalyst prepared in comparative example 2.

Detailed Description

The present invention will be described in detail with reference to the following embodiments.

Example 1

And (3) preparing the supported zinc-tin composite catalyst with the molar ratio of the zinc element to the tin element being 9: 1. 5.3g of zinc nitrate hexahydrate and 0.4g of stannous chloride dihydrate are stirred and dissolved in 200mL of deionized water to prepare a precursor solution. 0.4g of carbon black was added to the precursor solution and sonicated for 10min to disperse uniformly. 1.6g of sodium hydroxide was weighed out and prepared to 1 mol. L^-1The sodium hydroxide solution (2) was injected at a rate of 1 mL/min using a syringe pump^-1Is added dropwise to the precursor solution containing carbon black. Keeping the reaction temperature at about 80 ℃, and magnetically stirring the precursor solution in the dropping process. And monitoring the pH value of the reaction system by using an acidimeter in the dripping process, and keeping the pH value to slowly increase. After the dropwise adding, stirring is continued for 3h, and aging is carried out for 12 h. Then separating out solid particles by using a vacuum filtration device, washing the solid particles for 3 times by using deionized water, drying the solid particles in a vacuum drying oven, grinding the dried solid particles, roasting the ground solid particles for 2 hours at the temperature of 600 ℃ to obtain a product catalyst, and recording the product catalyst as Zn_0.9Sn_0.1O_z/C。

In examples 2-7, the composition of the precursor solution was varied, and supported zinc-tin composite catalysts, respectively designated as Zn, were prepared according to the procedure described in example 1, with molar ratios of zinc element to tin element of 8:2, 7:3, 5:5, 3:7, 2:8, and 1:9, respectively_0.8Sn_0.2O_z/C、Zn_0.7Sn_0.3O_z/C、Zn_0.5Sn_0.5O_z/C、Zn_0.3Sn_0.7O_z/C、Zn_0.2Sn_0.8O_zC and Zn_0.1Sn_0.9O_zand/C. In order to clearly show the correspondence of the specific examples to the catalysts prepared, the following table is given.

Table 1 corresponding list of examples and catalysts

Example numbering	Catalyst and process for preparing same
		Example 1	Zn_0.9Sn_0.1O_z/C
Example 2	Zn_0.8Sn_0.2O_z/C
		Example 3	Zn_0.7Sn_0.3O_z/C
Example 4	Zn_0.5Sn_0.5O_z/C
		Example 5	Zn_0.3Sn_0.7O_z/C
Example 6	Zn_0.2Sn_0.8O_z/C
		Example 7	Zn_0.1Sn_0.9O_z/C

In order to compare the performance of the zinc-tin composite catalyst, the invention also prepares a nano tin oxide catalyst and a nano zinc oxide catalyst.

Comparative example 1

And (3) preparation of the supported nano tin oxide catalyst. 2.2g of stannous chloride dihydrate is stirred and dissolved in 200mL of deionized water to prepare a precursor solution. 0.3g of carbon was added to the precursor solutionBlack and sonicate for 10min to disperse evenly. 0.8g of sodium hydroxide was weighed out and prepared to 1 mol. L^-1The sodium hydroxide solution (2) was injected at a rate of 1 mL/min using a syringe pump^-1Is added dropwise to the precursor solution containing carbon black. Keeping the reaction temperature at about 80 ℃, and magnetically stirring the precursor solution in the dropping process. And monitoring the pH value of the reaction system by using an acidimeter in the dripping process, and keeping the pH value to slowly increase. After the dropwise adding, stirring is continued for 3h, and aging is carried out for 12 h. Then separating out solid particles by using a vacuum filtration device, washing the solid particles for 3 times by using deionized water, drying the solid particles in a vacuum drying oven, grinding the dried solid particles, roasting the ground solid particles for 2 hours at the temperature of 600 ℃ to obtain a product catalyst, and marking the product catalyst as SnO₂/C。

Comparative example 2

And (3) preparation of the supported nano zinc oxide catalyst. 3.0g of zinc nitrate hexahydrate is dissolved in 200mL of deionized water under stirring to prepare a precursor solution. 0.3g of carbon black was added to the precursor solution and sonicated for 10min to disperse uniformly. 0.8g of sodium hydroxide was weighed out and prepared to 1 mol. L^-1The sodium hydroxide solution (2) was injected at a rate of 1 mL/min using a syringe pump^-1Is added dropwise to the precursor solution containing carbon black. Keeping the reaction temperature at about 80 ℃, and magnetically stirring the precursor solution in the dropping process. And monitoring the pH value of the reaction system by using an acidimeter in the dripping process, and keeping the pH value to slowly increase. After the dropwise adding, stirring is continued for 3h, and aging is carried out for 12 h. And then separating solid particles by using a vacuum filtration device, washing the solid particles for 3 times by using deionized water, drying the solid particles in a vacuum drying oven, grinding the dried solid particles, and roasting the ground solid particles for 2 hours at the temperature of 600 ℃ to obtain a product catalyst, namely ZnO/C.

The composite materials prepared in examples 1 to 7 and comparative examples 1 to 2 were used as cathode catalysts, Ir black was used as anode catalysts, and Nafion115 membrane (DuPont) was used as a proton exchange membrane, and a membrane electrode was prepared by directly spraying catalyst slurry on the membrane. The titanium mesh is used as a support layer and a current collecting layer of the membrane electrode. The working areas of the anode and cathode electrodes are both 5cm^-2And the loading amount of the metal catalyst is 1mg cm^-2. And (3) introducing electrolyte into the electrolytic cell in the test process. Cathode concentration at 16.4 mL/min^-1At a flow rate of KHCO₃The solution was added at 50 mL/min^-1CO is introduced at a flow rate₂A gas. The anode concentration was 32.8 mL/min^-1The KOH solution was passed through at a flow rate of (c). The test temperature was 25 ℃.

FIG. 1 shows Zn prepared in example 1_0.9Sn_0.1O_zX-ray diffraction pattern of/C catalyst, showing that the composition of the catalyst comprises Zn₂SnO₄、SnO₂And ZnO three phases with an average grain size of 22 nm.

FIG. 2 is Zn prepared in example 1_0.9Sn_0.1O_zC and SnO₂The polarization curve of the/C catalyst at a voltage of 2.6V has a polarization time of 3600 s. As can be seen, Zn was observed at the same potential_0.9Sn_0.1O_zThe current density of the/C catalyst is less than that of SnO₂the/C catalyst is high and SnO can be seen₂The current density of the/C catalyst tends to decrease with time, while Zn_0.9Sn_0.1O_zThe current density of the/C catalyst is stable in the test process of 3600s, and does not have a descending trend. Shows that the stability of the catalyst of the invention is superior to SnO₂a/C catalyst.

FIG. 3 is Zn prepared in example 1_0.9Sn_0.1O_zC and SnO₂Current efficiency histograms for the/C catalyst at different potentials. Zn can be clearly seen from the figure_0.9Sn_0.1O_zThe current efficiencies of formic acid of the/C catalyst at different potentials are higher than that of SnO at the same potential₂Current efficiency of the/C catalyst, and Zn_0.9Sn_0.1O_zThe formic acid current efficiency of the/C catalyst at 2.6V reached a maximum of 92.2%.

FIG. 4 shows the zinc-tin composite catalysts prepared in examples 1 to 7 and SnO prepared in comparative example 1₂Graph of the change in current efficiency of formic acid continuously tested over 24 hours at a potential of 2.6V for the/C catalyst. Zn_0.9Sn_0.1O_zThe formic acid current efficiency of the/C catalyst is maintained above 90% and tends to a steady state, while SnO₂The formic acid current efficiency of the/C catalyst is obviously reduced, the reduction speed of the formic acid current efficiency is increased along with the change of time, and the stability is poor.

FIG. 5 is a bar graph of formic acid current efficiencies at 2.6V potentials for the zinc-tin composite catalysts prepared in examples 1-7 and the ZnO/C catalyst prepared in comparative example 2. Compared with ZnO/C catalyst, the zinc-tin composite catalyst has much higher formic acid efficiency under 2.6V potential. The catalytic selectivity of the zinc-tin composite catalyst is better than that of a ZnO/C catalyst.

Tables 2 to 10 show the zinc-tin composite catalysts prepared in examples 1 to 7 and SnO prepared in comparative examples 1 and 2₂The catalytic performances of the/C, ZnO/C catalyst include current density at different electrolysis voltages, formic acid current efficiency and formic acid partial current density.

Table 2 Zn prepared in example 1_0.9Sn_0.1O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.2	2.4	2.6	2.8
					Current density/mA.cm^-2	15.2	25.8	36	50
Formic acid partial current density/mA cm^-2	11.4	21.7	33.2	39
					Current efficiency of formic acid	75.1％	84.2％	92.2％	82.03％

Table 3 Zn prepared in example 2_0.8Sn_0.2O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.4	2.6	2.8
				Current density/mA.cm^-2	14	20	36
Formic acid partial current density/mA cm^-2	10.1	17.9	29
				Current efficiency of formic acid	71.9％	89.6％	80.6％

Table 4 Zn prepared in example 3_0.7Sn_0.3O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.4	2.6	2.8
				Current density/mA.cm^-2	25	36	56
Formic acid partial current density/mA cm^-2	16.6	31.7	38.1
				Current efficiency of formic acid	66.3％	88.1％	68.1％

Table 5 Zn prepared in example 4₀₅Sn₀₅O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.4	2.6	2.8
				Current density/mA.cm^-2	19	29	54
Formic acid partial current density/mA cm^-2	13	23.7	32.6
				Current efficiency of formic acid	68.6％	81.8％	60.4％

Table 6 Zn prepared in example 5_0.3Sn_0.7O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.4	2.6	2.8
				Current density/mA.cm^-2	15	26	30
Formic acid partial current density/mA cm^-2	8.4	21.7	19.9
				Current efficiency of formic acid	55.7％	83.3％	66.2％

Table 7 Zn prepared in example 6_0.2Sn_0.8O_zElectrocatalytic performance of/C catalyst at different potentials

voltage/V	2.4	2.6	2.8
				Current density/mA.cm^-2	19	30	50
Formic acid partial current density/mA cm^-2	13.7	25.1	38.7
				Current efficiency of formic acid	72.3％	83.7％	77.4％

Table 8 Zn prepared in example 7_0.1Sn_0.9O_zElectrocatalytic performance of/C catalyst at different potentials

TABLE 9 SnO prepared by comparative example 1₂Electrocatalytic performance of/C catalyst at different potentials

voltage/V	2.2	2.4	2.6	2.8
					Current density/mA.cm^-2	9.6	15	23	29.8
Formic acid partial current density/mA cm^-2	6.5	10.8	19.9	19.4
					Current efficiency of formic acid	67.4％	72.3％	86.6％	65.2％

TABLE 10 electrocatalytic performance of ZnO/C catalyst prepared in COMPARATIVE DOCUMENT 2 at different potentials

voltage/V	2.2	2.4	2.6
				Current Density/mA cm^-2	27.1	38.6	52.4
Formic acid partial current density/mA cm^-2	2.9	8.8	16.6
				Current efficiency of formic acid	10.6％	22.7％	31.6％
Efficiency of CO current	65.9％	54.6％	45.3％

As can be seen from tables 2 to 10, the prepared zinc-tin composite catalyst has an increase in current density with an increase in voltage. The catalyst catalyzes CO within a certain voltage range₂The current efficiency for converting into formic acid increases with the increase of voltage, the formic acid current efficiency reaches the maximum when reaching 2.6V, the voltage exceeds 2.6V, the current efficiency is reduced, and the optimal voltage when obtaining the formic acid efficiency maximum is 2.6V. SnO₂the/C catalysts also exhibit the same variation. The ZnO/C catalyst has low selectivity to formic acid, generates byproducts such as CO and the like, and has low formic acid current efficiency. In particular, the catalyst Zn_0.9Sn_0.1O_zthe/C showed excellent CO₂The formic acid efficiency under 2.6V voltage is 92.2 percent under the condition of electric reduction activity, and the formic acid current efficiency under 2.2V voltage reaches 75.1 percent compared with SnO₂The catalyst/C and ZnO/C are still high at 2.4V, and the zinc-tin composite catalystThe agent has better long-term stability, and Zn is continuously tested under the voltage of 2.6V for 24 hours_0.9Sn_0.1O_zThe formic acid efficiency of the/C catalyst can still be kept above 90 percent, while SnO₂The formic acid efficiency of the/C catalyst then decreased to 66%.

The catalyst provided by the invention is a zinc-tin composite oxide catalyst, the preparation method is simpler in specific steps, and the catalyst catalyzes CO₂Selectively converted into formic acid. Zinc-tin composite catalysts, especially Zn_0.9Sn_0.1O_zthe/C composite catalyst has higher CO₂Relatively pure SnO with electroreduction catalytic activity₂the/C has higher stability, better formic acid selectivity than ZnO/C catalyst, and electrolytic cell electrolytic voltage can be even as low as 2.2V, CO₂The highest efficiency of converting into formic acid can reach 92.2 percent, and Zn_0.9Sn_0.1O_zthe/C composite catalyst shows more excellent long-term stability.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it should be understood that various changes and modifications can be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

The technical solution of the present invention has been disclosed above by the preferred embodiments. Those skilled in the art will recognize that changes and modifications can be made thereto without departing from the scope and spirit of the invention as disclosed in the appended claims.

Claims

1. The catalyst for electrochemically reducing carbon dioxide into formic acid is characterized in that the catalyst is carbon-supported nano Zn_xSn_yO_zWherein x is more than or equal to 0.8<1，0<y≤0.2，x+y＝1。

2. Catalyst according to claim 1, characterized in that the nano-Zn_xSn_yO_zGrain size ofIs 20-30 nm.

3. The catalyst of claim 1 wherein the carbon content of the catalyst is 50% and less by mass of the total mass of the catalyst.