CN111101143A

CN111101143A - Electrolyte for water electrolysis and water electrolysis hydrogen production system

Info

Publication number: CN111101143A
Application number: CN202010111038.1A
Authority: CN
Inventors: 朱威; 许照祥; 庄仲滨
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2020-02-24
Filing date: 2020-02-24
Publication date: 2020-05-05

Abstract

The invention discloses an electrolyte for electrolyzing water, which comprises water and an acid electrolyte and is characterized by further comprising a perfluorinated organic additive with the carbon atom number not more than 6. The novel electrolyte composition can effectively reduce the overpotential of the electrode and reduce the influence of bubbles on the effective working area of the electrode. The invention also provides a method and a system for producing hydrogen by electrolyzing water by using the electrolyte.

Description

Electrolyte for water electrolysis and water electrolysis hydrogen production system

Technical Field

The invention relates to hydrogen production by water electrolysis, in particular to an electrolyte for hydrogen production by water electrolysis.

Background

The water electrolysis hydrogen production technology is a key way in the field of clean hydrogen production, but is limited by high hydrogen production cost and develops slowly. Among them, the overpotential of bubbles caused by the gas evolution of the cathode and anode is one of the key technical problems causing low energy efficiency of electrolytic water and short electrode life. In particular, in the industrial production of electrolytic water, a large current is generally required, and a large amount of bubbles are generated on the surface of the electrode. When the bubbles can not be separated from the surface of the electrode immediately, the effective working area of the electrode is reduced, the reaction is prevented from continuing, and the overpotential of the reaction is increased.

Chinese patent application CN109995232A discloses a modulation power supply suitable for hydrogen production by water electrolysis, which modulates constant voltage dc into dc with a certain duty ratio, reduces the heating loss of the electrode plate during hydrogen production, reduces the influence of bubble effect on the effective electrolysis area of the electrode plate, and thus improves current efficiency.

Chinese patent application CN109183066A discloses a graphite-based electrode plate for hydrogen production by electrolyzing water, which can quickly desorb the hydrogen in an adsorbed state by increasing active sites on the surface of the electrode plate and inhibiting the growth of bubbles.

Therefore, the problems that the effective working area of the electrode in the electrolytic water is reduced due to the influence of bubbles and the reaction overpotential is enhanced are not considered to be solved from the perspective of the electrolyte in the prior art.

Disclosure of Invention

The invention aims to provide a novel electrolyte for producing hydrogen by electrolyzing water, which solves the problem that the effective working area of an electrode is reduced and the reaction overpotential is increased when bubbles cannot be separated from the surface of the electrode immediately in the prior water electrolysis technology.

The invention provides an electrolyte for electrolyzing water, which comprises water and an acid electrolyte and is characterized by further comprising a perfluorinated organic additive with the carbon atom number not more than 6.

In some of these embodiments, the perfluorinated organic additive is selected from at least one of perfluorobutylsulfonate, perfluoropropylsulfonate, perfluoroethylsulfonate, perfluoropentylsulfonate, perfluorohexylsulfonate, perfluorobutylsulfonyl fluoride, perfluoro (2-ethoxyethane) sulfonate.

In some embodiments, the electrolyte further comprises one of trihydroxy polyoxypropylene ether, tributyl phosphate, polyoxypropylene ethylene oxide glycerol ether, and n-heptanol.

In some embodiments, the mass concentration of the perfluorinated organic additive in the electrolyte is 0.01 g/L-1 g/L.

In some embodiments, the mass concentration of the perfluorinated organic additive in the electrolyte is 0.05 g/L-0.2 g/L.

In some of these embodiments, the electrolyte further comprises an optional inert supporting electrolyte.

The invention also provides a method for producing hydrogen by electrolyzing water, which uses the electrolyte.

The invention also provides a water electrolysis hydrogen production system which comprises a voltage output device, an anode, a cathode and the electrolyte, wherein the electrolyte is the electrolyte.

The invention can effectively reduce the overpotential of the electrode and reduce the influence of bubbles on the effective working area of the electrode by using the novel electrolyte composition. Compared with the electrolyte without adding organic molecules, the overpotential for hydrogen evolution and oxygen evolution of electrolyzed water can be reduced by 20% under the same heavy current after adding the organic molecules; under the same high overpotential, the current of hydrogen evolution and oxygen evolution of the electrolyzed water can be improved by 30 percent. In addition, bubbles are generated and separated more quickly after organic molecules are added, and the gas mass transfer on the surface of the electrode is improved.

Drawings

FIG. 1 shows the results of testing the cathode reaction performance of example 1 and comparative example 1 at a rotating speed of 1600 r/min;

FIG. 2 shows the results of testing the cathode reaction performance of example 1 and comparative example 1 at a rotating speed of 900 r/min;

FIG. 3 shows the results of the cathode reaction performance test of example 2 and comparative example 2;

FIG. 4 shows the results of the cathodic reaction chronopotentiometric performance tests of example 2 and comparative example 2;

FIG. 5 shows the results of the anode reaction performance test of example 3 and comparative example 3;

FIG. 6 is the results of the electrolyzed water test of example 4 and comparative example 4 in the range of-2.5V to-1V;

FIG. 7 shows the results of the test of electrolyzed water in the range of 1V to 2.5V for example 4 and comparative example 4;

FIG. 8 shows the results of the anode reaction performance test of example 5 and comparative example 5;

FIG. 9 shows the results of the cathode reaction performance test of example 5 and comparative example 5.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It is to be noted that, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

When bubbles can not be separated from the surface of the electrode immediately in the process of hydrogen production by water electrolysis, the effective working area of the electrode is reduced, the reaction is prevented from continuing, and the overpotential of the reaction is increased. The reduction of the electrolysis efficiency caused by the problem is always an important problem which troubles the industry of producing hydrogen by electrolyzing water. To solve this problem, various attempts have been made in the industry, including voltage control, electrode design. The main means is also to focus on the material selection of the electrode, the structural design and the manner of electrode additive.

The invention provides a strategy for introducing special organic molecules into the electrolyte to reduce the interfacial tension of bubbles in the water electrolysis process, accelerate the separation rate of the bubbles on the surface of an electrode, obviously reduce the overpotential of the bubbles and simultaneously reduce the foaming influence. The method can be applied to two half reactions of cathode Hydrogen Evolution Reaction (HER) and anode Oxygen Evolution Reaction (OER) of electrolyzed water to reduce overpotential.

Specifically, the invention discloses an electrolyte for electrolyzing water, which comprises water, an acid electrolyte and a perfluorinated organic additive with the carbon atom number not more than 6.

The perfluoro organic additive with the carbon number not more than 6 comprises a fluorocarbon chain group and a hydrophilic group which are connected with each other. Hydrophilic groups include, but are not limited to, sulfonate, ether, carboxyl, hydroxyl. The hydrogen atoms on the hydrocarbon chain in the fluorocarbon chain group are all replaced by fluorine atoms, the number of carbon atoms is not more than 6, preferably not more than 5, and the influence of the additive on the overpotential of the electrolyzed water and the separation of bubbles from the electrode is optimized through the control of the number of the carbon atoms. The perfluorinated organic additive with the carbon number not more than 6 designed by the invention has high surface activity, high thermal stability and high chemical stability, and when a monomolecular layer is formed on the surface of the solution by adsorption, the surface of the solution is equivalently covered by a layer of fluorocarbon chains, so that the surface tension can be reduced to be very low. In addition, the organic additive designed by the invention can reduce the surface tension of water, solution, suspension and the like, prevent foam from forming, or reduce or eliminate original foam, and is easy to degrade in nature.

By adding the special organic additive, the electrolyte for electrolyzing water disclosed by the invention can effectively reduce the overpotential of hydrogen evolution and oxygen evolution of electrolyzed water, improve the efficiency of separating bubbles from the surface of the electrode and increase the effective working area of the electrode, thereby improving the energy efficiency of electrolyzed water. It should be noted that the organic additives are of various types, and the special type of organic additives capable of solving the problems of the present invention can be obtained only by the deep recognition of the inventor on the problem of water electrolysis, the consideration of various factors and a large number of screening experiments.

In some embodiments, the perfluoro organic additive having not more than 6 carbon atoms is selected from at least one of perfluorobutylsulfonate, perfluoropropylsulfonate, perfluoroethylsulfonate, perfluoropentylsulfonate, perfluorohexylsulfonate, perfluorobutylsulfonyl fluoride, perfluoro (2-ethoxyethane) sulfonate.

The mass concentration of the perfluoro organic additive having not more than 6 carbon atoms in the electrolyte is 0.01 to 1g/L, preferably 0.05 to 0.5 g/L.

In some embodiments, the electrolyte further comprises one of trihydroxy polyoxypropylene ether, tributyl phosphate and polyoxypropylene ethylene oxide glycerol ether, and the mass concentration of the trihydroxy polyoxypropylene ether, the tributyl phosphate and the polyoxypropylene ethylene oxide glycerol ether is not more than 0.2g/L, and the mass concentration of the polyoxypropylene ethylene oxide glycerol ether is not more than 0.1 g/L. Better electrolysis effect can be obtained by combining one of trihydroxy polyoxypropylene ether, tributyl phosphate and polyoxypropylene ethylene oxide glycerol ether with perfluorinated organic additives with the carbon atom number not more than 6.

In some embodiments, trihydroxy polyoxypropylene ether, tributyl phosphate, and polyoxypropylene ethylene oxide glycerol ether can also be used alone as an organic additive, for example, an electrolyte comprising water, an acidic electrolyte, and trihydroxy polyoxypropylene ether, or an electrolyte comprising water, an acidic electrolyte, and tributyl phosphate, or an electrolyte comprising water, an acidic electrolyte, and polyoxypropylene ethylene oxide glycerol ether at a concentration of no more than 0.1g/L by mass.

In some embodiments, the electrolyte further comprises an optional inert supporting electrolyte. Inert electrolytes include, but are not limited to, sulfates, chlorides.

The invention also provides a method for producing hydrogen by electrolyzing water, which uses the electrolyte to produce hydrogen by electrolyzing water.

In some embodiments, the water electrolysis hydrogen production system is a liquid flow water electrolysis system, and the electrolyte is an electrolyte as described above. In some embodiments, the flow electrolytic water system is made of a transparent organic glass plate such as polymethyl methacrylate (PMMA).

The following is further illustrated with reference to specific examples.

Example 1

An electrolyte composition for electrolyzing water comprises sulfuric acid, water, trihydroxy polyoxypropylene ether, wherein H₂SO₄The concentration of (b) was 0.5mol/L, and the concentration of trihydroxy polyoxypropylene ether was 0.1 g/L.

In Standard threeThe test was carried out in an electrode test system using a working electrode coated with 0.1mg/cm²Commercial 20% Pt/C glassy carbon electrode, Pt wire for counter electrode, Saturated Calomel Electrode (SCE) with jacket for reference electrode, saturated argon atmosphere, and rotating disc speed of 1600r/min and 900 r/min. The cyclic voltammetry test was performed using a Princeton electrochemical workstation at a potential of-0.63V to 0.27V (relative to the reversible hydrogen electrode potential).

Example 2

An electrolyte composition for the electrolysis of water comprising sulfuric acid, water, potassium perfluorobutylsulfonate, wherein H₂SO₄The concentration of (2) was 0.5mol/L, and the concentration of potassium perfluorobutylsulfonate was 0.1 g/L.

In a standard three-electrode test system, the working electrode was coated with 0.1mg/cm²Commercial 20% Pt/C double hydrophilic carbon paper, Pt wire for the counter electrode, Saturated Calomel Electrode (SCE) with jacket for the reference electrode, and saturated argon atmosphere. Cyclic voltammetry tests and chronoamperometry tests were performed using a preston electrochemical workstation. The cyclic voltammetry potential is-0.63V-0.27V (relative to the reversible hydrogen electrode potential), and the chronoamperometric constant current is-0.12A.

Example 3

Same as example 2, except that the working electrode was coated with 0.4mg/cm²Commercial IrO₂The counter electrode of the double hydrophilic carbon paper is Pt wire, the reference electrode is Saturated Calomel Electrode (SCE) with jacket, and argon atmosphere is saturated. Cyclic voltammetry tests were performed using a preston electrochemical workstation at a potential of 1.07V to 2.27V (relative to the reversible hydrogen electrode potential).

Example 4

Same as example 2, except that the test system was a flow cell, in a flow cell water electrolysis device, 0.4mg/cm of coating would be applied²Commercial IrO₂Coated with 0.1mg/cm of carbon paper²Commercial 20% Pt/C carbon paper and 117nafion film are hot-pressed into a film electrode, both sides are respectively connected with copper sheets, one side is connected with an electrochemical workstation working electrode, the other side is connected with an electrochemical workstation counter electrode and a reference electrode, and both sides can be interchanged. Electrolyte solution of 0.5M H₂SO₄And the organic molecule potassium perfluorobutylsulfonate (0.1g/L) was added, and the electrolyte was circulated at a flow rate of 20ml/min using a peristaltic pump. And (3) performing cyclic voltammetry test by using a Princeton electrochemical workstation, wherein the test potential of the electrolyzed water is 1V-2.5V and-2.5V-1V respectively.

Example 5

The same as in example 4, except that the three-electrode system was used for the test. The reference electrode was Ag/AgCl. IrO in the case of oxygen evolution reaction₂The side of the electrochemical workstation working electrode is connected with a Pt/C side electrochemical workstation counter electrode; when hydrogen evolution reaction is carried out, Pt/C side is connected with an electrochemical workstation working electrode, IrO₂The electrochemical workstation counter electrode is flanked. Cyclic voltammetry tests were performed using the preston electrochemical workstation at potentials of 1.07V-2.27V and-0.63V-0.27V (relative to the reversible hydrogen electrode potential).

Comparative example 1

Unlike example 1, the electrolyte was H at a concentration of 0.5mol/L₂SO₄An aqueous solution.

Comparative example 2

Unlike example 2, the electrolyte was H at a concentration of 0.5mol/L₂SO₄An aqueous solution.

Comparative example 3

Unlike example 3, the electrolyte was H at a concentration of 0.5mol/L₂SO₄An aqueous solution.

Comparative example 4

Unlike example 4, the electrolyte was H at a concentration of 0.5mol/L₂SO₄An aqueous solution.

Comparative example 5

Unlike example 5, the electrolyte was H at a concentration of 0.5mol/L₂SO₄An aqueous solution.

As can be illustrated by fig. 1 and 2, the performance of the rotating disk electrodes at the same rotation speed is attenuated from the 1 st to the 8 th circles. After the trihydroxy polyoxypropylene ether is added, the performance attenuation degree from the 1 st circle to the 8 th circle is greatly reduced at a high rotating speed of 1600 r/min; at low rotation speed of 900r/min, the performance of the 1 st circle and the 8 th circle can be improved. Therefore, the organic molecule trihydroxy polyoxypropylene ether is added into the electrolyte to reduce the cathode reaction overpotential in the rotating disk electrode.

As can be seen from fig. 3, example 2 has a larger current than comparative example 2 at the same overpotential; at the same current, example 2 has a lower overpotential than comparative example 2. As can be seen from fig. 4, at the same constant potential I ═ 120mA, the overpotential was lower with the addition of potassium perfluorobutylsulfonate. Therefore, the addition of the potassium perfluorobutyl sulfonate in the electrolyte can reduce the over potential of the cathode reaction in the electrolytic cell.

As can be seen from fig. 5, the current of example 3 is larger than that of comparative example 3 at the same overpotential; at the same current, example 3 has a lower overpotential than comparative example 3. Therefore, the addition of the organic molecule potassium perfluorobutyl sulfonate in the electrolyte can reduce the overpotential of the anode reaction in the electrolytic cell.

As can be seen from fig. 6 and 7, example 4 has a larger current than comparative example 4 at the same electrolytic water voltage; in example 4, the voltage was lower than that in comparative example 4 under the same electrolytic water current. Therefore, the organic molecule potassium perfluorobutyl sulfonate is added into the electrolyte to improve the water electrolysis performance of the flow battery.

As can be seen from fig. 8 and 9, example 5 has a larger current than comparative example 5 at the same overpotential; at the same current, example 5 has a lower overpotential than comparative example 5. Therefore, the organic molecule potassium perfluorobutyl sulfonate is added into the electrolyte to improve the reaction performance of the cathode and the anode in the flow battery.

In addition, the water electrolysis process of examples 1-5 showed less blistering and faster detachment from the electrode surface due to the special additives of the present invention, reducing the effect of blistering on the electrode reaction.

In conclusion, the electrolyte for electrolyzing water provided by the invention can effectively reduce the overpotential of the electrode and reduce the influence of bubbles on the effective working area of the electrode, and is verified in a plurality of test systems.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. An electrolyte for electrolyzing water, which comprises water and an acid electrolyte, and is characterized in that the electrolyte also comprises a perfluorinated organic additive with the carbon number not more than 6.

2. The electrolyte according to claim 1, wherein the perfluoro organic additive is at least one selected from the group consisting of perfluorobutanesulfonate, perfluoropropanesulfonate, perfluoroethanesulfonate, perfluoropentanesulfonate, perfluorohexanesulfonate, perfluorobutanesulfonyl fluoride, and perfluoro (2-ethoxyethane) sulfonate.

3. The electrolyte of claim 1, further comprising one of trihydroxy polyoxypropylene ether, tributyl phosphate, polyoxypropylene oxyethylene glyceryl ether, and n-heptanol.

4. The electrolyte according to claim 1 to 3, wherein the mass concentration of the perfluorinated organic additive in the electrolyte is 0.01 to 1 g/L.

5. The electrolyte according to claim 4, wherein the mass concentration of the perfluoro organic additive in the electrolyte is 0.05g/L to 0.2 g/L.

6. The electrolyte of claims 1-3, further comprising an optional inert supporting electrolyte.

7. A method for producing hydrogen by electrolyzing water, characterized in that the electrolyte of any one of claims 1 to 6 is used.

8. A water electrolysis hydrogen production system is characterized by comprising a voltage output device, an anode, a cathode and an electrolyte, wherein the electrolyte is the electrolyte in any one of claims 1-6.