Electrolyte and method for preparing methane by inhibiting hydrogen evolution reaction in CO2 electroreduction process

Abstract

The invention relates to the technical field of carbon dioxide electroreduction, in particular to an electrolyte and method for preparing methane by inhibiting hydrogen evolution reaction in the CO2 electroreduction process, the electrolyte is an aqueous solution of inorganic salt, cations of the inorganic salt comprise alkali metal cations, and anions of the inorganic salt comprise Cl <-> and HCO3 <->. According to the method, methane is selectively prepared by using the composite electrolyte containing chloride ions and bicarbonate ions in an environment with a neutral pH value, and a hydrogen evolution reaction in electrochemical reduction of carbon dioxide is effectively inhibited. According to the method, the composite electrolyte containing chloride ions and bicarbonate ions is used, the catalyst is optimized, the pH value of the electrolyte and the reaction potential selectivity are regulated and controlled, so that the Faraday efficiency of methane is improved, and the Faraday efficiency of methane and ethylene in the product is regulated and controlled by changing the molar ratio of the chloride ions to the bicarbonate ions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon dioxide electro-reduction, and particularly relates to an electrolyte for inhibiting hydrogen evolution reaction in the process of CO2 electro-reduction and a method. BACKGROUND

[0002] Fixing and converting the main greenhouse gas CO2 into high-value carbon-based fuels and chemicals is one of the effective measures to reduce its emission, which has great environmental benefits. Compared with other CO2 fixation methods, electrochemical reduction can realize the reaction at normal temperature and pressure, with mild conditions and simple operation, and can realize selective synthesis of products by controlling the reaction conditions, which has better application prospect. Among them, methane has become an extremely attractive target product due to its high energy density and direct use of natural gas infrastructure.

[0003] At present, the preparation of methane by electro-reduction of CO2 usually adopts a liquid electrolyte reaction device, which at least comprises a cathode chamber, an anode chamber and a diaphragm separating the two. The cathode chamber is loaded with a cathode catalyst, which is usually a solid material and is divided into three categories: metal catalyst, non-metal catalyst and molecular catalyst. Among all metal catalysts, Cu shows unique electrocatalytic ability, which can generate small molecular hydrocarbons and alcohol products such as methane, ethane, ethylene and ethanol. Oxidation reaction occurs in the anode chamber. A direct current voltage is applied to the anode and cathode, so that CO2 undergoes multi-electron reduction reaction on the surface of the cathode catalyst to generate carbon monoxide, formic acid, methane, ethylene and other carbon-based products. The whole reaction process is usually carried out at normal temperature or low temperature, under normal pressure, in aqueous solution or non-aqueous electrolyte. Bicarbonate (such as KHCO3) is often used as electrolyte because it can provide CO2 source and maintain the pH stability of the reaction system.

[0004] However, there are problems such as hydrogen evolution reaction competition and low product selectivity in the process of electrochemical reduction of CO2, especially bicarbonate electrolyte will promote hydrogen evolution reaction at the reduction potential. Under high concentration or high overpotential conditions, the faradic efficiency of hydrogen can exceed 40 %, which seriously restricts the practical application of the technology.

[0005] Therefore, it is a technical problem to be solved in the field to develop an electrochemical reduction method that can inhibit hydrogen evolution reaction and improve methane selectivity. SUMMARY

[0006] One of the purposes of the present application is to provide an electrolyte for inhibiting hydrogen evolution reaction in the process of CO2 electro-reduction, which can achieve the selective preparation of methane and also achieve a certain effect of inhibiting hydrogen evolution, and the faradic efficiency of CO2 electrochemical reduction for preparing methane can be improved to 50 % by adjusting the proportion of the electrolyte.

[0007] The second object of the present application is to provide a method for selectively preparing methane and ethylene and inhibiting hydrogen evolution in the electrochemical reduction of CO2, which has simple process, mild reaction conditions, good long-term stability, simple waste liquid treatment, and can achieve the effect of inhibiting hydrogen evolution under the premise of selectively preparing methane and ethylene.

[0008] The scheme adopted by the one of the objects of the present application is an electrolyte for inhibiting hydrogen evolution reaction in the process of CO2 electro-reduction to prepare methane, wherein the electrolyte is an aqueous solution of inorganic salt, the cation of the inorganic salt includes alkali metal cation, and the anion includes Cl - and HCO3 - .

[0009] Preferably, the total ion concentration of the electrolyte is 0.4-1.8 mol / L.

[0010] Preferably, the alkali metal cation includes at least one of K + , Na + , and Li + .

[0011] Preferably, the alkali metal cation is K + .

[0012] Preferably, the molar ratio of Cl - to HCO3 - is 2-5:1.

[0013] Preferably, the molar ratio of Cl - to HCO3 - is 5:1.

[0014] The technical scheme adopted by the second object of the present application is a method for inhibiting hydrogen evolution reaction in the process of CO2 electro-reduction to prepare methane, comprising the following steps: (1) constructing a three-electrode system in an H-type electrolytic cell, and loading the electrolyte according to any one of claims 1-6; (2) introducing CO2 gas into the electrolyte in step (1), and adjusting the pH value to 6.8-7.4; (3) performing electrolysis reaction at normal temperature and pressure, and collecting the gaseous product at the upper part of the cathode chamber.

[0015] Preferably, in step (1), a silver / silver chloride electrode is used as a reference electrode, a platinum sheet is used as a counter electrode, and a carbon paper loaded with cuprous oxide electrocatalyst is used as a working electrode.

[0016] Preferably, in step (3), the cathode potential in the electrolysis reaction is-1.2 V to-1.5 V vs. RHE.

[0017] Preferably, in the electrolysis reaction, the cathode potential is -1.3 to -1.4 V vs. RHE.

[0018] Preferably, the electrical energy used for the electrochemical reduction of carbon dioxide is provided by renewable energy based on nuclear energy, hydroelectric energy, wind energy or solar energy.

[0019] Compared with the prior art, the present application has the following beneficial effects: The present application selectively produces methane in a neutral pH environment by using a composite electrolyte containing chloride ions and bicarbonate ions, and effectively suppresses the hydrogen evolution reaction in the electrochemical reduction of carbon dioxide.

[0020] The method of the present application selectively improves the faradic efficiency of methane by using a composite electrolyte containing chloride ions and bicarbonate ions, optimizing the catalyst, regulating the pH of the electrolyte and the reaction potential, and achieving the regulation of the faradic efficiency of methane and ethylene in the product by changing the molar ratio of chloride ions and bicarbonate ions.

[0021] The method of the present application uses cuprous oxide as an electrocatalyst, which has good long-term stability in the entire composite electrolyte system.

[0022] The electrolyte components used in the present application are simple to control, the reaction conditions are mild, the preparation process is simple, and the waste treatment is simple. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Example 1 of the present application; Figure 2 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Example 2 of the present application; Figure 3 The long-term stability curve of cuprous oxide in the composite electrolyte system in Example 2 of the present application; Figure 4 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Comparative Example 1 of the present application; Figure 5 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Comparative Example 2 of the present application; Figure 6 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Comparative Example 3 of the present application; Figure 7 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Comparative Example 4 of the present application; Figure 8 The faradic efficiency of each gaseous product in the electrochemical reduction of carbon dioxide in Comparative Example 5 of the present application; Figure 9Faraday efficiencies of each gaseous product of electrochemical reduction of carbon dioxide for the present comparative example 6. DETAILED DESCRIPTION In order to better understand the present application, the following examples are further illustrations of the present application, but the scope of the present application is not limited to the following examples.

[0024] Example 1 The electrocatalytic reduction of carbon dioxide was carried out in a well-sealed H-type electrolytic cell at room temperature by using CHI 760 E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum plate was used as the counter electrode, and a cuprous oxide-loaded carbon paper was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The two electrodes were separated by a Nafion 117 membrane.

[0025] (1) A composite electrolyte of 0.2 mol / L potassium chloride and 0.1 mol / L potassium bicarbonate was prepared.

[0026] (2) The composite electrolyte in step (1) was loaded into the H-type electrolytic cell, and carbon dioxide was introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0027] (3) After electrolysis at a cathode potential of -1.1 V (vs. RHE) for 30 min, the gaseous products generated during the electrolysis were determined by gas chromatography by measuring the integral area, and then the gaseous concentration was calculated by converting the integral area, and the Faraday efficiencies of different gaseous products were further calculated.

[0028] (4) The cathode potential was gradually adjusted to -1.2 V, -1.3 V, -1.4 V, and -1.5 V (vs. RHE), and step (3) was repeated.

[0029] Figure 1 The Faraday efficiencies of each gaseous product of electrochemical reduction of carbon dioxide at different potentials in the present example are shown in the figure. As can be seen from the figure, the gaseous products of electrochemical reduction of carbon dioxide in the 0.2 M KCl / 0.1 M KHCO3 composite electrolyte are methane, carbon monoxide, and ethylene. When the cathode potential is 1.3 V (vs. RHE), the main gaseous products of carbon dioxide reduction are methane and ethylene, and the Faraday efficiency of methane is greater than that of ethylene. As the cathode potential increases, the Faraday efficiency of methane begins to rise, and it has a certain effect on inhibiting hydrogen evolution, with a Faraday efficiency of hydrogen below 20%, and the lowest value being 5%, indicating that the use of KCl and KHCO3 composite electrolyte is beneficial to the production of methane and also has a certain effect on inhibiting hydrogen evolution.

[0030] Example 2 The electrocatalytic reduction of carbon dioxide was carried out in a well-sealed H-type electrolytic cell at room temperature by using CHI 760 E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum plate was used as the counter electrode, and a cuprous oxide-loaded carbon paper was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The two electrodes were separated by a Nafion 117 membrane.

[0031] (1) A composite electrolyte of 0.5 mol / L potassium chloride and 0.1 mol / L potassium bicarbonate was prepared.

[0032] (2) The composite electrolyte in step (1) was loaded into an H-type electrolytic cell, and carbon dioxide was introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0033] (3) After electrolysis at a cathode potential of -1.1 V (vs. RHE) for 30 min, the gas-phase products generated during the electrolysis were determined by gas chromatography by integrating the area, and then the gas concentration was calculated by converting the integral area, and the faradaic efficiency of different gas-phase products was further calculated.

[0034] (4) The cathode potential was gradually adjusted to -1.2 V, -1.3 V, -1.4 V, and -1.5 V (vs. RHE), and step (3) was repeated.

[0035] Figure 2 The faradaic efficiency of each gas-phase product of the electrochemical reduction of carbon dioxide at different potentials in this example is shown in the figure. As can be seen from the figure, the gas-phase products of the electrochemical reduction of carbon dioxide in the composite electrolyte of 0.5 M KCl / 0.1 M KHCO3 are methane, carbon monoxide, and ethylene. At all potentials, the main gas-phase products of the reduction of carbon dioxide are methane and ethylene, and the faradaic efficiency of methane is greater than that of ethylene, indicating that the composite electrolyte greatly promotes the production of methane on the basis of inhibiting the hydrogen evolution side reaction, and the faradaic efficiency of methane can reach up to 51%. In addition, the faradaic efficiency ratio of methane and ethylene can reach up to 13, greatly promoting the selectivity of carbon dioxide reduction to a single product, and indicating the superiority of the composite electrolyte.

[0036] Figure 3 The long-term stability curve of cubic phase cuprous oxide in the composite electrolyte system in this example is shown in the figure. As can be seen from the figure, the current density and the faradaic efficiency of methane can maintain good stability.

[0037] Comparative Example 1 The electrocatalytic reduction of carbon dioxide was carried out in a well-sealed H-type electrolytic cell at room temperature by using CHI 760 E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum plate was used as the counter electrode, and a cuprous oxide-loaded carbon paper was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The cathode and the anode were separated by a Nafion 117 membrane.

[0038] (1) A 0.1 mol / L potassium bicarbonate solution was prepared as the electrolyte.

[0039] (2) The electrolyte in step (1) was loaded into the H-type electrolytic cell, and carbon dioxide was introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0040] (3) After electrolysis at a cathode potential of -1.1 V (vs. RHE) for 30 min, the gas-phase products generated during the electrolysis were determined by gas chromatography by integrating the area, and then the gas concentration was calculated by converting the integral area, and the faradaic efficiency of different gas-phase products was further calculated.

[0041] (4) The cathode potential was gradually adjusted to -1.2 V, -1.3 V, -1.4 V, and -1.5 V (vs. RHE), and step (3) was repeated.

[0042] As shown in Figure 4 the faradaic efficiency of each gas-phase product of the electrochemical reduction of carbon dioxide at different potentials in the present comparative example. As can be seen from the figure, the gas-phase products of the electrochemical reduction of carbon dioxide in the 0.1 M KHCO3 electrolyte by cubic cuprous oxide are methane, carbon monoxide, and ethylene. When the potential is -1.2 V (vs. RHE), methane begins to be converted. When the potential is -1.3 V (vs. RHE), the main gas-phase products of the reduction of carbon dioxide are methane and ethylene, and the faradaic efficiencies of the two are not significantly different. The overall faradaic efficiency of methane is not high at all potentials, and the overall faradaic efficiency of hydrogen is at a high level, and increases with increasing cathode potential, indicating that when 0.1 M KHCO3 is used as the electrolyte, the higher the cathode potential, the more serious the hydrogen evolution side reaction, and the faradaic efficiency of methane is not high. The inhibition of hydrogen evolution and the selectivity of methane are not as good as in Examples 1 and 2.

[0043] Comparative Example 2 The electrocatalytic reduction of carbon dioxide was carried out in a well-sealed H-type electrolytic cell at room temperature using a CHI 760 E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum sheet was used as the counter electrode, and a carbon paper loaded with cuprous oxide was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The two electrodes were separated by a Nafion 117 membrane.

[0044] (1) A 0.5 mol / L potassium bicarbonate solution was prepared as the electrolyte.

[0045] (2) The electrolyte in step (1) was loaded into the H-type electrolytic cell, and carbon dioxide was introduced to adjust the pH to 6.8-7.4 before electrolysis.

[0046] (3) After electrolysis at a cathode potential of -1.0 V (vs. RHE) for 30 min, the gas-phase products generated during the electrolysis were determined by gas chromatography by integrating the area, and then the gas concentration was calculated by converting the integral area, and the faradaic efficiency of different gas-phase products was further calculated.

[0047] (4) The cathode potential was gradually adjusted to -1.1 V, -1.2 V, -1.3 V, and -1.4 V (vs. RHE), and step (3) was repeated.

[0048] Figure 5 The faradaic efficiency of each gas-phase product of the electrochemical reduction of carbon dioxide at different potentials in the present comparative example is shown in the figure. As can be seen from the figure, the gas-phase products of the electrochemical reduction of carbon dioxide in the 0.5 M KHCO3 solution with cubic cuprous oxide are methane, carbon monoxide, and ethylene. When the potential is -1.1 V (vs. RHE), methane begins to be converted, and the main gas-phase product of the reduction of carbon dioxide is methane and ethylene, but the overall faradaic efficiency of methane is not high, and the faradaic efficiency of hydrogen is much higher than that of methane and ethylene. This indicates that the effect of KHCO3 alone as the electrolyte on suppressing hydrogen evolution is poor, and compared with Figure 4 the effect of suppressing hydrogen evolution becomes worse and worse with the increase of the concentration of the KHCO3 solution and the increase of the cathode potential, and the faradaic efficiency of methane further decreases. The effect of suppressing hydrogen evolution and the selectivity of methane are both not as good as those of Examples 1 and 2.

[0049] Comparative Example 3 The electrocatalytic reduction of carbon dioxide was carried out in a well-sealed H-type electrolytic cell at room temperature using a CHI 760 E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum sheet was used as the counter electrode, and a carbon paper loaded with cuprous oxide was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The two electrodes were separated by a Nafion 117 membrane.

[0050] (1) Preparation of 0.1 mol / L potassium chloride solution as electrolyte.

[0051] (2) The electrolyte in step (1) is filled into the H-type electrolytic cell, and carbon dioxide is introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0052] (3) After electrolysis at a cathode potential of -1.1 V (vs. RHE) for 30 min, the integral area of the gas phase product generated during electrolysis is determined by gas chromatography, and then the integral area is converted to obtain the gas concentration, and further calculate the faraday efficiency of different gas phase products.

[0053] (4) Adjust the cathode potential step by step -1.2 V, -1.3 V, -1.4 V, -1.5 V (vs. RHE) Repeat step (3).

[0054] Figure 6 The faraday efficiency of each gas phase product of electrochemical reduction of carbon dioxide at different potentials in the present comparative example is shown in the figure, from which it can be seen that the performance of cubic cuprous oxide in the electro-reduction of carbon dioxide in 0.1 M KCl solution can be found that the gas phase products of carbon dioxide reduction are methane, carbon monoxide and ethylene, with the increase of cathode potential, the ratio of faraday efficiency of methane to ethylene becomes larger, but it can be obviously observed that the faraday efficiency of hydrogen increases with the increase of cathode potential, which indicates that with the increase of cathode potential, the hydrogen evolution side reaction becomes more obvious, and it is difficult to effectively inhibit hydrogen evolution. In addition, the starting conversion potential of methane is relatively high (-1.4 V vs. RHE), and the effect of inhibiting hydrogen evolution is poor in this potential range.

[0055] Comparative Example 4 At room temperature, the electrocatalytic reduction of carbon dioxide was carried out in a good airtight H-type electrolytic cell by using CHI 760E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as a reference electrode, a platinum sheet was used as a counter electrode, and a cuprous oxide-loaded carbon paper was used as a working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber, and the cathode and anode were separated by Nafion 117 membrane.

[0056] (1) Preparation of 0.5 mol / L potassium chloride solution as electrolyte.

[0057] (2) The electrolyte in step (1) is filled into the H-type electrolytic cell, and carbon dioxide is introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0058] (3) The integral area of the gas phase product generated during electrolysis was determined by gas chromatography after electrolysis at a cathode potential of -1.2 V (vs. RHE) for 30 min, and then the gas concentration was converted from the integral area, and the faradic efficiency of different gas phase products was further calculated.

[0059] (4) The cathode potential was adjusted step by step to -1.2 V, -1.3 V, -1.4 V, -1.5 V (vs. RHE), and step (3) was repeated.

[0060] Figure 7 The faradic efficiency of each gas phase product of the electrochemical reduction of carbon dioxide at different potentials in the present comparative example is shown in the figure. As can be seen from the figure, the gas phase products of the electrochemical reduction of carbon dioxide in the electrolyte of 0.5 M KCl are methane, carbon monoxide and ethylene. When the potential is -1.2 V (vs. RHE), the main gas phase product of the reduction of carbon dioxide is methane and ethylene, and the faradic efficiency of methane is higher than that of ethylene. However, the overall faradic efficiency of methane is not high. With the increase of the cathode potential, the faradic efficiency of hydrogen is also increased. The use of 0.5 M KCl electrolyte alone cannot effectively inhibit the hydrogen evolution reaction, and the conversion rate of methane is also further reduced. Figure 6

[0061] Comparative Example 5 At room temperature, the electrocatalytic reduction of carbon dioxide was carried out in a H-type electrolysis cell with good airtightness by using a CHI 760E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as a reference electrode, a platinum sheet was used as a counter electrode, and a cuprous oxide-loaded carbon paper was used as a working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The cathode and the anode were separated by a Nafion 117 membrane.

[0062] (1) A composite electrolyte of 0.1 mol / L potassium chloride and 0.1 mol / L potassium bicarbonate was prepared.

[0063] (2) The composite electrolyte in step (1) was loaded into the H-type electrolysis cell, and carbon dioxide was introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0064] (3) The integral area of the gas phase product generated during electrolysis was determined by gas chromatography after electrolysis at a cathode potential of -1.2 V (vs. RHE) for 30 min, and then the gas concentration was converted from the integral area, and the faradic efficiency of different gas phase products was further calculated.

[0065] (4) The cathode potential was adjusted step by step to -1.3 V, -1.4 V, -1.5 V, -1.6 V (vs. RHE), and step (3) was repeated.​

[0066] Figure 8 The faradic efficiency of each gaseous product of electrochemical reduction of carbon dioxide at different potentials in the present comparative example is shown. As can be seen from the figure, the gaseous products of electrochemical reduction of carbon dioxide in 0.1 M KCl / 0.1 M KHCO3 solution by cubic cuprous oxide are methane, carbon monoxide and ethylene. When the potential is -1.3 V (vs. RHE), the main gaseous products of carbon dioxide reduction are methane and ethylene. When the potential is -1.4 V (vs. RHE), the faradic efficiency of methane is higher than that of ethylene, but the overall faradic efficiency of methane is not high. The faradic efficiency of hydrogen increases with the increase of cathode potential, indicating that when the KCl concentration in the composite electrolyte is too low, it cannot play a role in inhibiting the hydrogen evolution side reaction.

[0067] Comparative Example 6 The electrocatalytic reduction of carbon dioxide was carried out at room temperature in a well-sealed H-type electrolytic cell using a CHI 760E electrochemical workstation. A standard three-electrode system was used, in which a silver-silver chloride electrode was used as the reference electrode, a platinum sheet was used as the counter electrode, and a cuprous oxide-loaded carbon paper was used as the working electrode. The reference electrode and the working electrode were placed in the cathode chamber, and the counter electrode was placed in the anode chamber. The cathode and anode were separated by a Nafion 117 membrane.

[0068] (1) A composite electrolyte of 0.8 mol / L potassium chloride and 0.1 mol / L potassium bicarbonate was prepared.

[0069] (2) The composite electrolyte in step (1) was loaded into the H-type electrolytic cell, and carbon dioxide was introduced to adjust the pH value to 6.8-7.4 before electrolysis.

[0070] (3) After electrolysis at a cathode potential of -1.1 V (vs. RHE) for 30 min, the gaseous products generated during electrolysis were determined by gas chromatography by integrating the area, and then the gas concentration was calculated by converting the integral area, and the faradic efficiency of different gaseous products was further calculated.

[0071] (4) The cathode potential was gradually adjusted to -1.2 V, -1.3 V, -1.4 V and -1.5 V (vs. RHE), and step (3) was repeated.

[0072] Figure 9The faradic efficiency of each gaseous product of electrochemical reduction of carbon dioxide at different potentials in the present embodiment is shown. As can be seen from the figure, the gaseous products of electrochemical reduction of carbon dioxide by cubic cuprous oxide in the composite electrolyte of 0.8 M KCl / 0.1 M KHCO3 are methane, carbon monoxide and ethylene. When the potential is-1.3 V (vs. RHE), the main gaseous products of carbon dioxide reduction are methane and ethylene. It is worth noting that only at a potential of-1.5 V (vs. RHE), the faradic efficiency of methane is higher than that of ethylene. In addition, the faradic efficiency of hydrogen remains below 20% at all potentials, indicating that although increasing the concentration of KCl solution can still inhibit the hydrogen evolution side reaction, it does not significantly improve the faradic efficiency of methane.

[0073] Table 1 Faradic efficiency of hydrogen, methane and ethylene in different electrolyte systems (-1.4 V vs. RHE)

[0074] As can be seen from the data in Table 1, under the condition of a certain cathode potential, the composite electrolyte containing chloride ions and bicarbonate ions in the present application can achieve a certain effect of inhibiting hydrogen evolution in a neutral pH environment while achieving the selective preparation of methane and ethylene. By adjusting the ratio of the electrolyte, the faradic efficiency of electrochemical reduction of CO2 to prepare methane can be increased to 50%.

[0075] The above is only a preferred embodiment of the present application, of course, cannot be limited to the scope of the present application, should be noted that, for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and changes, these improvements and changes are also considered to be within the scope of the present application.

Claims

1. An electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane, characterized in that, The electrolyte is an aqueous solution of an inorganic salt, wherein the cations of the inorganic salt include alkali metal cations, and the anions include Cl-. - and HCO3 - .

2. The electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane according to claim 1, characterized in that, The total electrolyte ion concentration is 0.4 - 1.8 mol / L.

3. The electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane according to claim 1, characterized in that, The alkali metal cations include K + Na + Li + At least one of them.

4. The electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane according to claim 3, characterized in that, The alkali metal cation is K. + .

5. The electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane according to claim 1, characterized in that, The Cl - and HCO3 - The molar ratio is 2-5:

1.

6. The electrolyte for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane according to claim 5, characterized in that, The Cl - and HCO3 - The molar ratio is 5:

1.

7. A method for suppressing the hydrogen evolution reaction during CO2 electroreduction to prepare methane, characterized in that, Includes the following steps: (1) Construct a three-electrode system in an H-type electrolytic cell and fill it with the electrolyte as described in any one of claims 1-6; (2) Introduce CO2 gas into the electrolyte in step (1) and adjust the pH value to 6.8-7.4; (3) Under normal temperature and pressure, an electrolysis reaction is carried out, and gaseous products are collected in the upper part of the cathode chamber.

8. The method for preparing methane by suppressing the hydrogen evolution reaction during CO2 electroreduction according to claim 7, characterized in that: In step (1), in the three-electrode system, a silver / silver chloride electrode is used as the reference electrode, a platinum sheet is used as the counter electrode, and carbon paper loaded with the electrocatalyst cuprous oxide is used as the working electrode.

9. The method for preparing methane by suppressing the hydrogen evolution reaction during CO2 electroreduction according to claim 7, characterized in that: In step (3), the cathode potential in the electrolysis reaction is -1.2 V to -1.5 V vs. RHE.

10. The method for preparing methane by suppressing the hydrogen evolution reaction during CO2 electroreduction according to claim 9, characterized in that: In the electrolysis reaction, the cathode potential is -1.3 to -1.4 V vs. RHE.

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