Acid CO2 electrolysis method

Abstract

The invention discloses an acidic CO2 electrolysis method, and belongs to the technical field of electrochemical electrolysis. The method comprises the following steps: adding tetramethyl ammonium salt into an acidic catholyte, dissolving and ionizing tetramethyl ammonium cation TMA < + >, contacting the acidic catholyte with inflowing CO2 gas to form an electrolytic reaction system, and carrying out electrocatalytic reduction reaction under an electrolytic condition to generate a carbon-based product. On the basis of effective regulation and control of TMA < + > on an electro-catalysis CO2 reduction double-electrode layer interface, efficient conversion of CO2 to a target product is achieved, the salting-out phenomenon can be avoided in the long-time electrolysis process, the operation life even exceeds 2600 h under the industrial related current density, and excellent activity, selectivity and stability are shown; according to the method, components of the acidic electrolyte of the electrocatalytic reduction CO2 system are redesigned, and a new idea can be provided for designing a novel alkali-metal-free ion mediated acidic CO2 electrolysis system in the future.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical electrolysis and particularly relates to an acidic CO 2 Electrolysis method, in particular to an electrocatalytic CO in an acidic medium mediated by tetramethylammonium cation 2 Method of restoration. Background Art

[0002] CO 2 It is one of the main gases causing the greenhouse effect. The greenhouse effect will lead to global temperature rise, ocean acidification, glacier melting and other problems, which seriously hinder the sustainable development of human society. Actively formulate and implement a comprehensive carbon treatment plan to reduce CO 2 Emissions are extremely necessary.

[0003] CO 2 Electrochemical reduction technology (CO 2 ER is a process that converts CO2 into 2 The method of converting it into high-value-added energy fuels and chemical products can also simultaneously achieve long-term storage of intermittent renewable energy, providing a feasible solution to global warming and energy crisis. It has huge application potential and has therefore attracted widespread attention from technicians in this field.

[0004] Traditional CO 2 Electrolysis technology usually relies on alkaline / neutral solutions as electrolytes, but in alkaline and neutral reaction systems, CO 2 Easy to react with hydroxide (OH - ) react to form carbonates or bicarbonates, resulting in CO 2 The loss will also reduce the energy conversion efficiency and stability of the reaction system. 2 Electroreduction can not only alleviate the problem of salt accumulation, but also improve CO 2 The single-pass conversion rate (often exceeding 50%) and the energy conversion efficiency of generating the target product are the main reasons for developing the electrocatalytic reduction of CO in acidic systems. 2 The reaction has attracted much attention in recent years. However, in acidic systems, due to the + The concentration of water is very high, and the water reduction hydrogen evolution (HER) competition reaction will be more intense, which will lead to CO 2 The Faradaic efficiency of electroreduction is lower than that of alkaline or neutral systems. Therefore, it is of great significance to design a catalytic reduction process with high selectivity and stability in an acidic environment.

[0005] Introducing alkali metal cations (such as K + , Li + , Cs +Specifically, alkali metal cations are physically adsorbed on the electrode surface, regulating the double electric layer electric field distribution on the electrode surface, thereby inhibiting the movement of hydronium ions, reducing competitive hydrogen evolution reactions, and thus improving CO 2 In addition, alkali metal cations can stabilize CO through electrostatic interactions or direct coordination. 2 Reduction reaction intermediates, promoting CO 2 Activation to generate formic acid, CO or multi-carbon compounds. However, over time, systems with added alkaline metal cations often face the problem of salt precipitation on the gas diffusion electrode (GDE), mainly due to the local accumulation of metal cations combined with carbonate anions, resulting in the precipitation of bicarbonate. This precipitation will destroy the hydrophobicity of the electrode, and then cause flooding, that is, the abnormal aggregation of electrolyte on the electrode surface, affecting the normal progress of the electrolysis process. In addition, when a proton exchange membrane is used to separate the anode and cathode electrolytes, alkali metal ions may also pass through the proton exchange membrane, causing the composition of the anode and cathode electrolytes to gradually change over time. This change will further affect the stability of the electrolysis system, reducing the controllability and repeatability of the electrolysis process.

[0006] To achieve stable acidic conditions CO 2 Electroreduction technology developed for acidic CO 2 The key is the new alkali-free metal ion electrolysis system of the electrolysis method. However, from the perspective of the published alternatives, the existing strategies either cannot eliminate the carbonates generated at the interface of the electroreduction system, affecting the stability during long-term operation (generally no more than 150 hours); or cannot effectively inhibit the acidic electrocatalytic CO 2 The violent hydrogen evolution side reaction that occurs during the reaction leads to a high selectivity of the hydrogen evolution side reaction. 2 For efficient electrolysis, a feasible solution is to regulate the local microenvironment at the interface of the electrocatalytic double layer.

[0007] Organic cations are another important class of cations in electrochemistry due to their large ion size, hydrophobicity, and unique solvation shell structure. Compared with metal cations, organic cations provide more opportunities to regulate the interfacial microenvironment through intermolecular interactions between their functional groups, water, and other active / inactive species in the double electrical layer. These characteristics make organic cations a promising alternative to traditional alkali metal cations as acidic CO 2 In principle, due to their cationic nature, organic cations in acidic electrolytes can screen the electric field from the cathode by accumulating on the Helmholtz plane, thereby inhibiting the migration of hydrogen ions and improving the acidic CO 2However, no relevant studies have shown that adding organic cations to the electrolyte can drive the acidic CO reduction alone. 2 Electrolysis, although those skilled in the art have tried to promote acidic CO 2 However, how these organic cations affect the acidic CO at the molecular level is still unclear. 2 The understanding of the electrolysis process lags far behind that of metal cations, which is mainly due to the more complex kinetic behavior of organic cations in the double layer. This complexity is related to their unique structure, which hinders the further development of the design of metal-free cation systems. The related processes and mechanisms of action need to be further explored. Summary of the invention

[0008] In view of the above problems, the present invention aims to provide an acidic CO 2 The electrolysis method introduces tetramethylammonium cations into the acidic electrolyte to electrocatalyze CO 2 The reduction double-layer interface can be effectively regulated to improve the activity, selectivity and stability of the reduction reaction.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows: an acidic CO 2 Electrolysis method, by adding tetramethylammonium salt to the acidic cathode electrolyte, dissolving it and ionizing tetramethylammonium cations, the acidic electrolyte and the inflowing CO 2 The gas contacts to form an electrolytic reaction system, and an electrocatalytic reduction reaction is carried out under electrolytic conditions to generate carbon-based products.

[0010] Furthermore, the tetramethylammonium salt is selected from salts that can stably exist in an acidic electrolyte and ionize tetramethylammonium cations, and the pH of the acidic electrolyte is less than 7.

[0011] Furthermore, the cathode electrolyte is a sulfuric acid aqueous solution, and the sulfuric acid concentration in the electrolyte is 0.01 to 1M.

[0012] Preferably, the tetramethylammonium salt is selected from one or more of tetramethylammonium chloride, tetramethylammonium hydroxide, tetramethylammonium phosphate and tetramethylammonium sulfate.

[0013] Furthermore, the voltage conditions for the electrocatalytic reduction reaction are -0.1V to -1.7V and the current is 0 to 300 mA cm -2 .

[0014] Furthermore, the carbon-based product is one or more of carbon monoxide, formic acid, methanol, ethanol, and ethylene.

[0015] Furthermore, the concentration of tetramethylammonium cations in the acidic electrolyte is 0.1 to 5M.

[0016] Furthermore, the inflow of CO 2 The flow rate is 0.5~50sccm.

[0017] Furthermore, the cathode catalyst is one of Au-based catalyst, Bi-based catalyst, Cu-based catalyst, Sn-based catalyst and In-based catalyst.

[0018] As can be seen from the embodiments, the present invention adds high concentration tetramethylammonium chloride molecules to sulfuric acid solution to ionize TMA. + , under strong acidic conditions CO 2 It is efficiently reduced to carbon monoxide, and the salt precipitation phenomenon during long-term electrolysis is completely avoided. The reaction activity, selectivity and stability are significantly improved. It is speculated that it is TMA + It exhibits a cation effect different from that of traditional alkali metal cations. Alkali metal cations mainly work by reducing the driving force of proton electromigration. TMA + HER is inhibited mainly by disrupting the hydrogen bonding network of proton shuttling.

[0019] The beneficial effects of the present invention are:

[0020] 1. This application discloses a method suitable for CO 2 Reduced tetramethylammonium cation (TMA + )-mediated acidic CO 2 Electrolysis method, by adding a certain amount of tetramethylammonium salt to the acidic electrolyte to ionize TMA + , TMA + Can electrocatalyze CO 2 Reducing the double electrical layer interface effectively controls the CO 2 The high efficiency conversion to the target product (close to 100% Faraday efficiency) and the single-pass carbon efficiency reached 85.1%, and the salt precipitation phenomenon can be avoided during the long-term electrolysis process, breaking the existing acidic CO 2 Limitations of electroreduction electrolyte application strategies;

[0021] 2. TMA proposed in this application + Acidic CO mediated 2 The electrolysis technology has the advantages of high Faradaic efficiency in generating products and no obvious salt precipitation. The technology can be used at industrially relevant current densities (100 mA cm -2 ) has an operating life of more than 2600h, and the advantage of no salt precipitation during the reaction is that the alkaline CO 2 It has also been proven in electrolysis technology, and the long-term stability exceeds 1200h;

[0022] 3. TMA proposed in this application +Acidic CO mediated 2 The electrolysis system not only electrocatalyzes CO 2 It exhibits excellent activity, selectivity and stability in CO production and plays an important role in promoting CO 2 The same is true for the conversion of ER into formic acid, and the selectivity of formic acid can reach more than 80%;

[0023] 4. By adjusting TMA in acidic electrolyte + The concentration of influent CO 2 The flow rate can affect the electrocatalytic CO 2 The Faraday efficiency and single-pass carbon utilization rate of the target product generated by reduction are further regulated to maximize the carbon utilization efficiency of the catalytic reaction;

[0024] 5. The acidic CO proposed in this application 2 Electrolysis is not only a method for electrocatalytic reduction of CO 2 The redesign of the acidic electrolyte components of the system also provides a basis for the design of new acidic CO 2 The electrolysis system provides new ideas. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The electrolysis system set up in Example 1 is used to electrocatalyze CO 2 Faradaic efficiency (FE) and local current density of different products produced during reduction test at specific potentials;

[0026] Figure 2 This is the result of a long-term stability test of the electrolysis system set up in Example 1;

[0027] Figure 3 is the XRD spectrum of the cathode working electrode before and after the electrocatalytic test in Example 1;

[0028] Figure 4 In Example 1, electrocatalytic CO 2 The Faradaic efficiency (FE) and local current density of the products produced during the reduction test at a specific potential;

[0029] Figure 5 In Example 2, different TMA + The electrolysis system with a concentration of 200 μg / cm2 was used for electrocatalytic CO 2 Faradaic efficiency (FE) and local current density of the products produced during the reduction test;

[0030] Figure 6 The electrocatalytic CO 2 Faradaic efficiency (FE) and formic acid current density of different products produced during reduction test at specific potentials;

[0031] Figure 7 The electrocatalytic CO 2 Faradaic efficiency and single-pass carbon efficiency for reduction tests;

[0032] Figure 8 The electrocatalytic CO 2 Faradaic efficiency (FE) and local current density of different products produced during reduction test at specific potentials;

[0033] Fig. 9 This is the result of a long-term stability test of the electrolysis system set up in Comparative Example 2;

[0034] Fig.10 The electrolysis system set up in Comparative Example 2 is used to electrocatalyze CO at different carbon dioxide flow rates. 2 Faradaic efficiency and single-pass carbon efficiency for reduction tests;

[0035] Fig.11 It is the XRD spectrum of the cathode working electrode before and after the electrocatalytic test based on the electrolysis system of Comparative Example 2;

[0036] Fig.12 In Example 3, electrocatalytic CO 2 The Faradaic efficiency of the product produced during the reduction test at a specific potential;

[0037] Fig.13 This is the result of a long-term stability test on the electrolysis system set up in Comparative Example 3. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0039] Example 1

[0040] This example develops a new alkali-free metal ion electrolysis system to break the existing acidic CO 2 Limitations of the application strategy of electroreduction electrolytes. Specifically, organic cations are introduced into acidic electrolytes to regulate the proton concentration at the electrocatalytic double layer interface (the purpose is to regulate the progress of the carbon dioxide reduction reaction and product selectivity) and thermodynamically stabilize carbon dioxide-related intermediates (to improve the efficiency of the reduction reaction and product purity).

[0041] When selecting cations, considering that organic cations should have both high solubility and minimum size in the corresponding carbonates to prevent salt precipitation and minimize HER kinetics, tetramethylammonium cation (TMA) was finally selected in this example. +) As an acidic supporting electrolyte, the solubility of tetramethylammonium cation-bicarbonate can reach ~12.4M, which is KHCO 3 (20℃, 3.62M) is 3.4 times.

[0042] Based on the catholyte supplemented with tetramethylammonium chloride for CO 2 The process of the electroreduction test is as follows:

[0043] Step 1. Preparation of cathode electrolyte: Weigh 548 g of tetramethylammonium chloride (McLean, AR, molecular weight 109.6) in a beaker, add water to dissolve, transfer to a 1000 mL volumetric flask, add sulfuric acid to complete the preparation of cathode electrolyte, the sulfuric acid concentration in the electrolyte is 0.05 M, and the tetramethylammonium cation concentration is 5 M.

[0044] In the second step, 0.5M sulfuric acid was used as the anode electrolyte, and the cathode catalyst was Au nanomaterial, which was loaded on carbon black at a ratio of 40wt% and then sprayed on the gas diffusion electrode as the working electrode. The anode electrocatalyst was IrO 2 / Ti, the reference electrode was Ag / AgCl (3.5M KCl).

[0045] The cathode catalyst was prepared as follows: 80 mg HAuCl 4 ·3H 2 O was dissolved in a mixed solvent of 2 mL of ethanol and 16 mL of oleylamine, heated to 150 °C in an oil bath with the lid open for 10 minutes, then tightly covered and heated to 220 °C for 30 minutes, cooled to room temperature, and centrifuged at 13500 rpm for 5 minutes to separate the solid product - gold nanoparticles supported on carbon (i.e., Au / C catalyst), then 4 mg of Au / C catalyst was added to 500 μL of ethanol, and 5 μL of Nafion was added and ultrasonicated for 40 minutes to obtain a uniform catalyst ink, which was evenly sprayed onto carbon paper (gas diffusion layer) and dried overnight.

[0046] Step 3: Electrocatalytic CO generation at different potentials in a flow cell electrocatalytic device 2 Reduction test, gaseous products were analyzed by gas chromatography and liquid products were analyzed by nuclear magnetic resonance spectroscopy.

[0047] Unless otherwise specified, the carbon dioxide input flow rate used was 50 sccm, the commercial carbon paper used was YLS-30T, and the back of the carbon paper was sprayed with a 1% polytetrafluoroethylene (PTFE) emulsion (1 cm -2 300 μL was sprayed on the surface and then dried under an infrared lamp).

[0048] The Faradaic efficiency and local current density of different products at specific potentials are as follows: Figure 1As shown in the figure, adding 5M TMA in acidic medium + The Faradaic efficiency of CO generation can reach over 90% in a wide potential range, which is comparable to that of the reversible hydrogen electrode (V RHE ) compared to -1.20V RHE Maximum FE at CO It is 99.1%.

[0049] Based on the electrolysis system disclosed in this embodiment, at an industrially relevant current density (100 mA cm -2 ) below -1.23V RHE Long-term electrolysis to obtain long-term stability test results ( Figure 2 ), after 2600h of electrolysis, the catalytic system can still remain stable, exceeding most of the CO 2 Electrocatalytic reduction system.

[0050] XRD spectra of the cathode working electrode before and after the electrocatalytic test are shown in Figure 3 ,from Figure 3 It can be seen that no carbonate is precipitated at the cathode working electrode before and after the test.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that tetramethylammonium chloride is not added to the cathode electrolyte, and the concentration of sulfuric acid in the cathode acidic electrolyte is 0.05M.

[0053] The same method was used to electrocatalyze CO 2 Reduction test, gas chromatography analysis of gas products, the corresponding product at a specific potential Faraday efficiency and local current density such as Figure 4 As shown, from Figure 4 It can be seen that in the absence of organic cations, the HER competitive reaction is dominant in the electrocatalytic system, resulting in only H 2 The carbon dioxide is not effectively activated.

[0054] Example 2

[0055] The difference between this embodiment and embodiment 1 is that the concentration of tetramethylammonium chloride in the cathode electrolyte is changed to form different TMA + Concentration electrolysis system for studying TMA + Concentration of acidic CO 2 Specifically, the concentration of sulfuric acid in the cathode electrolyte was kept constant at 0.05 M, and the TMA + The concentrations of were 0 M, 0.1 M, 0.5 M, 1 M, 2 M and 5 M, respectively. The other settings of the electrolysis system remained unchanged. The electrocatalytic CO2 Reduction test, detection of TMA + Selectivity and activity of electrocatalytic systems with different concentrations.

[0056] Test results see Figure 5 ,from Figure 5 The Faraday efficiency of CO generation increases steadily with the increase of tetramethylammonium cation concentration, and the CO generation rate is positively correlated with the concentration of tetramethylammonium cation, confirming that tetramethylammonium cation plays a role in promoting CO generation under strong acid conditions. 2 The kinetics of the conversion to CO plays a key role.

[0057] Example 3

[0058] The difference between Example 3 and Example 1 is that the cathode catalyst used in Example 1 is replaced with a Bi nanosheet catalyst to electrocatalyze CO 2 Formic acid production, other parameters and steps remained unchanged.

[0059] The synthesis method of Bi nanosheets is as follows: 20 mL of ethylene glycol is dispersed in 145 mg of Bi(NO 3 ) 3 ·5H 2 O, and then 4 mL NaBH 4 (2.25 mg / mL) was added at a rate of 16 mL / h to obtain a black precipitate at room temperature, which was centrifuged and dried to obtain a bismuth nanosheet catalyst.

[0060] The electrocatalytic CO 2 Restore test, test results see Figure 6 ,from Figure 6 It can be seen that under the action of Bi-based catalyst, the acidic CO 2 The selectivity of hydrogen generated in the electrolysis system can also be suppressed to less than 1%, and the selectivity of formic acid generated is maintained at a level greater than 80% in a wider potential range.

[0061] Example 4

[0062] The difference between this embodiment and embodiment 1 is that the flow rate of the inflowing carbon dioxide is changed to explore the effect of the flow rate of the carbon dioxide on the single-pass carbon utilization rate. The flow rates of the inflowing carbon dioxide are adjusted to 50, 30, 20, 10, 3, 1 and 0.5 sccm respectively, and the other steps and parameters remain unchanged. The electrocatalytic CO 2 electrocatalysis is carried out in the same manner as in embodiment 1. 2 Restore test, test results see Figure 7 The results show that as the inflow of CO 2 The decrease in flow rate, CO 2 The carbon utilization rate gradually increases.2 The carbon utilization rate reaches 85.1% when the input flow rate is 0.5 sccm, which means that more than 85% of the carbon dioxide can be converted into CO.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that potassium chloride is added to the cathode electrolyte instead of tetramethylammonium chloride, so that the sulfuric acid concentration in the electrolyte is 0.05M and the potassium ion concentration is 3M. ​​The electrocatalytic CO 2 Reduction test to detect electrocatalytic CO in potassium ion electrolyte system 2 Reduction selectivity, activity and stability.

[0065] The Faradaic efficiency and local current density of the corresponding products at a specific potential are as follows: Figure 8 As shown, combined Figure 8 It can be seen that when there is 3M potassium ions in the cathode electrolyte, the CO 2 The electroreduction reaction is dominant, but the selectivity of CO generation does not exceed 90% at each potential, and the hydrogen selectivity is greater than 10%. Compared with TMA + In terms of system, the selectivity of hydrogen evolution reaction in potassium ion system is still relatively high.

[0066] The electrolytic system was tested at -1.07V RHE The long-term stability under Fig. 9 As shown in the results, the long-term electrolysis in 3M potassium ion sulfuric acid electrolyte (pH ~ 0.7) only achieved 18h ​​stability, which is far less than TMA + Acidic CO mediated 2 Electrocatalytic reduction system.

[0067] The test was based on the electrolysis system for CO 2 During electrocatalytic reduction of CO 2 Effect of flow rate on single-pass carbon utilization, see Fig.10 ,from Fig.10 Look, with the input CO 2 The decrease in flow rate, CO 2 The carbon utilization rate gradually increases, but when CO 2 When the flow rate is as low as 0.5 sccm, the carbon utilization rate is only 36.5%, which means that only 36.5% of the carbon dioxide can be converted into CO. Compared with TMA + Acidic CO mediated 2 For electrocatalytic reduction system, CO 2 One-way utilization is at a low level.

[0068] Fig.11In order to conduct CO 2 XRD spectra of the cathode working electrode before and after electrocatalytic reduction. The graphical results show that potassium bicarbonate is significantly accumulated on the carbon paper after electrolytic reduction. This accumulated carbonate should be the cause of the instability of the electrolytic system.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that the cathode electrolyte used in the example is replaced with 3M tetramethylammonium hydroxide, the anode electrolyte is replaced with 1M potassium hydroxide, and the other steps and parameters remain unchanged to carry out electrocatalytic CO 2 Restore test, the result is as follows Fig.12 As shown, from Fig.12 It can be seen that when the cathode electrolyte is an alkaline electrolyte system without potassium ions, the Faradaic efficiency of CO generation can reach more than 90% within a wider potential range.

[0071] The long-term stability of the electrolysis system was tested. Fig.13 As shown, the alkaline system based on tetramethylammonium ions also achieved an electrolytic stability of more than 1200 hours, which is better than the catalytic durability test results of most potassium ion systems reported so far.

[0072] The above shows and describes the basic principles, main features and advantages of the present invention. However, the above is only a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other implementation methods derived by any technician in the field without departing from the technical solution of the present invention should be included in the scope of the present invention.

Claims

1. An acidic CO2 electrolysis method, characterized in that: Tetramethylammonium salt is added to the acidic cathode electrolyte to dissolve it and ionize tetramethylammonium cations. The cathode electrolyte contacts the inflowing CO2 gas to form an electrolytic reaction system, and an electrocatalytic reduction reaction is carried out under electrolytic conditions to generate carbon-based products.

2. An acidic CO2 electrolysis method according to claim 1, characterized in that: The tetramethylammonium salt is selected from salts that can stably exist in an acidic electrolyte and ionize tetramethylammonium cations, and the pH of the acidic electrolyte is less than 7.

3. An acidic CO2 electrolysis method as claimed in claim 2, characterized in that: The tetramethylammonium salt is selected from one or more of tetramethylammonium chloride, tetramethylammonium hydroxide, tetramethylammonium phosphate and tetramethylammonium sulfate.

4. The acidic CO2 electrolysis method according to claim 1, characterized in that: The voltage conditions for the electrocatalytic reduction reaction are -0.1V to -1.7V and the current is 0 to 300mAcm -2 .

5. The acidic CO2 electrolysis method according to claim 1, characterized in that: The carbon-based product is one or more of carbon monoxide, formic acid, methanol, ethanol, and ethylene.

6. The acidic CO2 electrolysis method according to claim 1, characterized in that: The concentration of tetramethylammonium cation in the acidic electrolyte is 0.1 to 5M.

7. The acidic CO2 electrolysis method according to claim 1, characterized in that: The flow rate of the inflowing CO2 is 0.5 to 50 sccm.

8. The acidic CO2 electrolysis method according to claim 1, characterized in that: The cathode catalyst is one of Au-based catalyst, Bi-based catalyst, Cu-based catalyst, Sn-based catalyst and In-based catalyst.

9. An acidic CO2 electrolysis method according to claim 1, characterized in that: The cathode electrolyte is a sulfuric acid aqueous solution, and the sulfuric acid concentration in the electrolyte is 0.01 to 1M.

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