Co-electrolysis method coupling carbon dioxide reduction and sulfide oxidation

Abstract

The present invention discloses a co - electrolysis method coupling carbon dioxide reduction and sulfide oxidation. The cathode of this co - electrolysis system is a carbon dioxide reduction gas diffusion electrode, and the anode is a direct sulfide oxidation electrocatalyst electrode, which is a co - electrolysis system coupling carbon dioxide reduction at the cathode and sulfide oxidation at the anode. It realizes the collection of carbon dioxide reduction products on the cathode side and the collection of solid sulfur products through series acid treatment on the anode side. Compared with the traditional carbon dioxide electro - reduction system, the anode of this co - electrolysis system replaces the water oxidation process with sulfide oxidation. The anode reaction substrate is sulfide, and the anode reaction potential is greatly reduced. At the same time, the anode electrolyte produces solid sulfur as a product through further acid treatment, effectively reducing the energy consumption of traditional carbon dioxide reduction. Meanwhile, high - value - added carbon dioxide reduction products and solid sulfur are produced, achieving "cost reduction and efficiency improvement" in CO2 electrolysis.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical technology and energy chemical industry, and specifically relates to a co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation. Background Art

[0002] The renewable energy revolution has become a global consensus to achieve carbon neutrality and the mission of sustainable development for mankind. Electrochemical CO2 reduction (CO2RR) can not only convert CO2 to produce energy fuels and basic chemicals, but also absorb green electricity from intermittent renewable energy, providing a promising solution for the renewable energy revolution.

[0003] The key challenge to the commercialization of CO2 electrolysis is its low energy conversion efficiency. Limited by the slow surface catalytic reaction of the anode and cathode, CO2 electrolysis requires huge energy consumption under commercial current, especially the oxygen evolution reaction (OER, 4OH - →O2+2H2O+4e - ) Due to its excessive overpotential, 90% of the input energy of CO2 electrolysis is consumed. Moreover, the OER anode only produces a low-value product, oxygen, at the anode, which seriously reduces the energy input-output efficiency of the entire electrolysis system. Therefore, the CO2RR-OER electrolysis system actually "wastes" most of the input electrical energy, affecting the sustainability of the entire electrolysis system. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and to provide a co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation; the co-electrolysis system can effectively reduce the energy consumption of traditional carbon dioxide reduction, while producing high value-added carbon dioxide reduction products and solid sulfur, thereby achieving "cost reduction and efficiency improvement" in CO2 electrolysis.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The co-electrolysis method of coupling carbon dioxide reduction and sulfide oxidation adopts a flowing electrolytic cell, with a carbon dioxide reduction gas diffusion electrode as the cathode and a sulfide direct oxidation electrode as the anode, to form a co-electrolysis system of carbon dioxide reduction and sulfide oxidation; during the electrolysis process, the sulfide is oxidized to a solid sulfur product;

[0007] The cathode collects the carbon dioxide reduction product, and the anode collects the solid sulfur product after series acid treatment.

[0008] A further improvement of the present invention is:

[0009] Preferably, the flow electrolytic cell is a three-chamber electrolytic cell, including a gas chamber, a cathode electrolyte chamber, and an anode electrolyte chamber, where the cathode electrolyte chamber and the anode electrolyte chamber are separated by a proton exchange membrane; the cathode electrolyte is a solution of potassium hydroxide, sodium hydroxide, potassium bicarbonate, or sodium bicarbonate; the anode electrolyte is a potassium hydroxide solution containing potassium sulfide or sodium sulfide, or a sodium hydroxide solution containing potassium sulfide or sodium sulfide.

[0010] Preferably, the carbon dioxide reduction gas diffusion electrode is a gas diffusion electrode with a gas diffusion substrate loaded with a carbon dioxide reduction electrocatalyst; the gas diffusion substrate is a hydrophobic carbon paper or polytetrafluoroethylene; the carbon dioxide reduction electrocatalyst is copper, bismuth, silver; or an alloy of any two or three phases of copper, bismuth, and silver; or an oxide of copper, bismuth, and silver; or a sulfide of copper, bismuth, and silver.

[0011] Preferably, the sulfide direct oxidation electrode is a substrate loaded with sulfur-doped metal hydroxide; the substrate is nickel foam or carbon cloth; the metal hydroxide is a metal hydroxide containing one or more of cobalt, nickel, copper, and iron; the preparation process of the sulfur-doped metal hydroxide is: soaking the electrode with the substrate loaded with the metal hydroxide in a sulfide solution to form the sulfur-doped metal hydroxide.

[0012] Preferably, the process of co-electrolysis in the co-electrolysis system is as follows: carbon dioxide gas is continuously supplied in the gas chamber, and the cathode electrolyte and the anode electrolyte are respectively introduced into the corresponding chambers; the cathode electrolyte and the anode electrolyte are circulated by a peristaltic pump;

[0013] When applying a potential for co-electrolysis, carbon dioxide gas on the cathode side permeates through the gas diffusion electrode to form a gas-solid-liquid three-phase interface, and is reduced at this three-phase interface. On the anode side, sulfide ions are directly oxidized on the catalyst surface to generate soluble polysulfides.

[0014] Preferably, the co-electrolysis process is powered by solar power generation, and the flow electrolytic cell is connected in series with a photovoltaic panel.

[0015] Preferably, the cathode collects carbon dioxide reduction products including gas products and liquid products. The gas products are collected through the gas chamber outlet, and the liquid products are collected from the cathode electrolyte; the process of collecting the anode solid sulfur product is: introducing the anode electrolyte containing polysulfides into an acidic solution or gas for acid treatment to generate a precipitate, collecting the precipitate and drying it to obtain solid sulfur.

[0016] Preferably, the gas products are one or more of CO, H2, CH4, and C2H4, and the liquid products are one or more of CH3OH, HCOO - 、C2H5OH、CH3COO - 、n-C3H7OH.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention discloses a co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation. The co-electrolysis method is based on the coupling of cathode carbon dioxide reduction and anode sulfide oxidation, and establishes a co-electrolysis system for carbon dioxide reduction and sulfide oxidation. Compared with the traditional carbon dioxide electroreduction system, the anode of the co-electrolysis system is replaced by sulfide oxidation by water oxidation, the anode reaction substrate is sulfide, the anode reaction potential is greatly reduced, and the anode electrolyte is further treated with acid to produce solid sulfur as a product, which effectively reduces the energy consumption of traditional carbon dioxide reduction, and produces high value-added carbon dioxide reduction products and solid sulfur at the same time, so as to achieve "cost reduction and efficiency improvement" of CO2 electrolysis. The anode sulfide oxidation proposed by the present invention replaces the water oxidation reaction, significantly reduces the energy consumption of carbon dioxide electrolysis, and obtains a high value-added solid sulfur product at the anode, which improves the economic output of carbon dioxide electrolysis. The co-electrolysis system can be co-electrolyzed by photovoltaic cells under illumination, and can also be further connected in series with a sulfur-containing pollutant treatment process to realize a solar-driven carbon dioxide reduction coupled with sulfur-containing wastewater / waste gas treatment process.

[0019] Furthermore, the sulfide oxidation of the present invention is direct sulfur oxidation in an alkaline electrolyte, which is a process of direct oxidation of sulfides, and the product is polysulfide, which avoids the catalyst poisoning caused by the precipitation of sulfur element during the sulfur oxidation process, and finally realizes the recovery of sulfur element by acid treatment of the polysulfide electrolyte.

[0020] Furthermore, the CO2RR-SOR co-electrolysis system constructed by the present invention can directly use photovoltaic power generation for co-electrolysis. Benefiting from the low potential requirement of CO2RR-SOR co-electrolysis, the solar-driven PV-EC co-electrolysis can be operated at a voltage greater than 100 mA / cm 2 It operates at a current density of , showing certain application prospects.

[0021] Furthermore, the present invention provides an emerging strategy to solve the problem of “energy waste” in CO2RR-OER electrolysis by replacing OER to minimize energy consumption while maximizing the economic benefits of CO2 electrolysis. - +OH - →S+H2O+2e -)The required reaction potential is only 0.142 V vs RHE. Compared with the 1.229 V potential of the OER reaction, the SOR requires lower energy consumption. Compared with the CO2RR-OER system, the energy demand of the CO2RR-SOR paired electrolysis is reduced. On the other hand, the anodic product of the SOR reaction is sulfur, and its market price ($0.22 / kg) is much higher than that of oxygen ($0.085 / kg). In terms of comparing the economic benefits output per unit of input energy, the profit of anodic SOR electrolysis is more than 20 times that of OER electrolysis. In addition, the substrate of SOR electrolysis is sulfide, which is a toxic pollutant harmful to the ecological environment. Its sources include H2S gas impurities in natural gas fields or sulfur-containing industrial sewage. Therefore, the SOR reaction has the characteristic of waste pollutant treatment, which further increases the economic value of the CO2RR-SOR co-electrolysis. Therefore, coupling CO2RR with SOR can simultaneously convert CO2 and conduct waste treatment, establishing a sustainable co-electrolysis process. Description of the Drawings

[0022] Figure 1 LSV curves of CO2RR-SOR co-electrolysis and CO2RR-OER co-electrolysis for producing formic acid and polysulfides in the examples.

[0023] Figure 2 Faradaic efficiency of formic acid at different current densities for CO2RR-SOR co-electrolysis to produce formic acid in the examples.

[0024] Figure 3 LSV curves of CO2RR-SOR co-electrolysis and CO2RR-OER co-electrolysis for producing multi-carbon products and polysulfides.

[0025] Figure 4 Faradaic efficiency of each product at different current densities for CO2RR-SOR co-electrolysis and CO2RR-OER co-electrolysis to produce multi-carbon products.

[0026] Figure 5 Schematic diagram of PV-EC co-electrolysis for sunlight-driven CO2RR-SOR co-electrolysis to produce formic acid.

[0027] Figure 6 Variation of the operating current density, Faradaic efficiency of formic acid, and cumulative concentration of polysulfides with time during continuous illumination of the formic acid production system by solar light-driven CO2RR-SOR co-electrolysis in Example 3.

[0028] Figure 7 Variation of the operating current density, Faradaic efficiency of formic acid, and cumulative concentration of polysulfides with time during continuous illumination of the formic acid production system by solar light-driven CO2RR-SOR co-electrolysis in Example 4.

[0029] Figure 8Pictures and XRD patterns of the solid sulfur collected after the anolyte is acid-treated. Detailed implementation mode

[0030] The present invention will be further described in detail below with reference to the accompanying drawings:

[0031] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to the present invention; the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0032] One embodiment of the present invention discloses a co-electrolysis method coupling carbon dioxide reduction and sulfide oxidation. This co-electrolysis method is based on the following system:

[0033] The co-electrolysis system uses a flow electrolytic cell. The cathode is a carbon dioxide reduction gas diffusion electrode, and the anode is an oxidation electrocatalyst. It is a co-electrolysis system for coupling carbon dioxide reduction at the cathode and sulfide oxidation at the anode, realizing the collection of carbon dioxide reduction products on the cathode side and the collection of solid sulfur products through serial acid treatment on the anode side.

[0034] Specifically, the flow electrolytic cell is a three-chamber electrolytic cell, including a gas chamber, a cathode electrolyte chamber, and an anode electrolyte chamber, where the cathode electrolyte chamber and the anode electrolyte chamber are separated by a proton exchange membrane; the cathode electrolyte uses potassium hydroxide, sodium hydroxide, potassium bicarbonate, or sodium bicarbonate solution, and the corresponding anode electrolyte uses a potassium hydroxide or sodium hydroxide solution containing potassium sulfide or sodium sulfide. The cathode electrolysis concentration range is 0.5 - 7M, the potassium / sodium sulfide concentration in the corresponding anode electrolyte is 0.5 - 3M, and the potassium / sodium hydroxide solution concentration range is 0.5 - 7M.

[0035] Specifically, the cathode is a gas diffusion electrode loaded with a carbon dioxide reduction electrocatalyst, where the carbon dioxide reduction electrocatalyst is disposed on a gas diffusion substrate; the gas diffusion substrate is carbon paper or polytetrafluoroethylene, and the carbon dioxide reduction electrocatalyst includes, but is not limited to, metals such as copper, bismuth, and silver, as well as alloys, metal oxides, or metal sulfides of the above metals. The cathode collects carbon dioxide reduction products including gas products and liquid products. The gas products are one or more of CO, H2, CH4, and C2H4, and the liquid products are one or more of CH3OH, HCOO - 、C2H5OH、CH3COO - 、n-C3H7OH.

[0036] Further, the above gas diffusion electrode loads the electrocatalyst onto the gas diffusion electrode substrate by means such as spraying, drop coating, or in-situ growth. The loading density of the electrocatalyst in terms of the metal element content is 1-4 mg / cm 2 .

[0037] The anode uses an oxidation electrocatalyst composed of a substrate and a sulfur-doped electrocatalyst. The sulfur-doped electrocatalyst is a sulfur-doped metal hydroxide, and the sulfur-doped metal hydroxide is loaded on the substrate; the substrate is a nickel foam substrate or a carbon cloth substrate, and the metal hydroxide is a metal hydroxide containing one or more of cobalt, nickel, copper, and iron. The metal hydroxide electrode is further immersed in a sulfide solution to form a sulfur-doped electrocatalyst.

[0038] Further, the anode loads the oxidation electrocatalyst onto substrates such as nickel foam or carbon cloth by means of hydrothermal synthesis, electrodeposition, drop coating, etc.; the above anode is immersed in a sulfide solution for treatment. The sulfide solution is potassium sulfide or sodium sulfide, with a concentration of 1 M and an immersion time of 10 min to 180 min.

[0039] The co-electrolysis process is that carbon dioxide gas is introduced into the gas chamber, and the cathode electrolyte and the anode electrolyte are respectively introduced into the corresponding chambers; during the electrolysis process, the gas is continuously introduced at a controlled flow rate, and the flow rate is 5-50 mL / min; the cathode / anode electrolyte is circulated by a peristaltic pump, and the flow rate is 1-10 mL / min; when applying a potential for co-electrolysis, the carbon dioxide gas on the cathode side penetrates through the gas diffusion electrode to form a gas-solid-liquid three-phase interface, and is reduced at this three-phase interface. On the anode side, sulfide ions are oxidized on the catalyst surface to form soluble polysulfides; the entire co-electrolysis system can operate continuously at a current density in the range of 50-300 mA / cm 2 range, and the cell voltage range is 0.5-4 V.

[0040] After electrolysis, the cathode carbon dioxide reduction products are related to the electrocatalysts used. Among them, for the Bi-based catalyst that produces formic acid, the Faraday efficiency of formic acid is greater than 80%. For the Cu-based catalyst that produces multi-carbon products, the Faraday efficiency of C2+ products is greater than 50%. For the Ag-based catalyst that produces CO products, the Faraday efficiency of CO is greater than 80%. The anode can maintain chemical stability in an alkaline solution containing 1M sodium sulfide or potassium sulfide, and also maintain electrochemical stability under an applied voltage of 2V vs RHE.

[0041] The gas products (one or more of CO, H2, CH4, C2H4) at the cathode end of the co-electrolysis system are collected through the gas chamber outlet, and the liquid products (one or more of CH3OH, HCOO - 、C2H5OH、CH3COO - 、n-C3H7OH) are collected from the cathode electrolyte; polysulfides are produced at the anode end, and solid sulfur can be collected through acid treatment; the acid treatment process is to introduce an acidic solution or gas into the anode electrolyte containing polysulfides. The acidic solution can be dilute sulfuric acid, dilute hydrochloric acid, etc., and the proton concentration of the solution is 1M; the acidic gas can be hydrogen sulfide gas or natural gas containing hydrogen sulfide impurities.

[0042] During the above electrolysis process, solar power generation can be used for co-power supply. The flow electrolysis cell is directly connected in series with a commercial photovoltaic panel to form a solar-driven photovoltaic-electrolysis system. Under the illumination of a xenon lamp simulating sunlight, CO2 can be continuously electrolytically reduced and sulfides can be oxidized, and the working current density is 100 - 150 mA / cm 2 .

[0043] The following is further illustrated with specific examples:

[0044] Example 1: CO2RR-SOR co-electrolysis to produce formic acid

[0045] (1) Preparation of sulfur-copper co-doped Co(OH)2 anode: Dissolve 0.1 mmol of copper nitrate trihydrate, 0.4 mmol of cobalt nitrate hexahydrate, and 0.35 g of urea in 17 mL of deionized water, and transfer it to a 50 mL hydrothermal autoclave with a polytetrafluoroethylene liner. Vertically immerse a 2*2 cm 2 nickel foam into the hydrothermal solution, and then place it in an oven at 120 °C for hydrothermal treatment for 6 hours. The obtained copper-doped Co(OH)2 product is washed and dried by electrodes, and then immersed in a solution mixed with 1M K2S and 1M KOH for half an hour for further sulfur doping to obtain sulfur-copper co-doped Co(OH)2, denoted as S-Cu:Co@NF.

[0046] (2) Preparation of a gas diffusion cathode loaded with electrochemically reduced Bi: Dissolve 0.970 g of bismuth nitrate pentahydrate and 0.5 g of CTAB powder in 60 ml of deionized water, and stir to form a homogeneous solution A; dissolve 3.0 g of urea in 40 ml of ethanol, and stir to form a homogeneous solution B. Then add solution B to solution A and stir for 30 min to form a white and uniform mixture. After a 4-h water bath at 90 °C, centrifuge and dry to obtain Bi precursor powder. Mix 10 mg of Bi precursor powder, 2 mL of ethanol, and 40 μL of Nafion binder, and sonicate for 2 h to obtain a slurry. Take 180 μL of the slurry and evenly drop it onto a 2 gas diffusion electrode based on carbon paper with dimensions of 1.5 * 1.5 cm, and dry it overnight at room temperature. Subsequently, perform in-situ electrochemical reduction in a flow electrolytic cell at 100 mA / cm 2 to obtain a Bi-based gas diffusion electrode, labeled as ER-Bi GDE.

[0047] (3) CO2RR-SOR co-electrolysis based on the ER-Bi GDE||S-Cu:Co@NF electrolytic cell: Assemble the ER-Bi GDE cathode and the S-Cu:Co@NF anode into a three-chamber flow cell electrolytic cell. Introduce CO2 into the gas chamber at a flow rate of 20 mL / min; use 1 M KOH and 1 M K2S + 1 M KOH as the cathode electrolyte and the anode electrolyte, respectively, and circulate them in the cathode chamber and the anode chamber through a peristaltic pump at a flow rate of 10 mL / min. Subsequently, perform CO2RR-SOR co-electrolysis in a two-electrode LSV test mode. This co-electrolysis system shows a low onset cell voltage of 0.75 V, and at a low cell voltage of 2.10 V, the co-electrolysis current density reaches 100 mA / cm 2 ( Figure 1 ). For comparison, use 1 M KOH as the anode electrolyte for CO2RR-OER co-electrolysis, and the cell voltage of the electrolytic cell needs to reach 3.43 V at 100 mA / cm2. The CO2RR-SOR co-electrolysis based on the ER-Bi GDE||S-Cu:Co@NF electrolytic cell reduces the energy consumption by 40% compared to CO2RR-OER co-electrolysis.

[0048] (4) Production of formic acid by CO2RR-SOR co-electrolysis at different current densities: Polarize the ER-Bi GDE||S-Cu:Co@NF electrolytic cell in a constant current mode to perform CO2RR-SOR co-electrolysis. Figure 2 Show the Faraday efficiencies of formic acid, the cathode CO2 reduction product, and hydrogen, the by-product, at different current densities. In the constant current polarization test range of 50 - 150 mA / cm 2 , the FE of HCOO - remains above 90%, and it is 95.1% at 100 mA / cm 2 .

[0049] Example 2: CO2RR-SOR Co-electrolysis for Producing Multi-Carbon Products

[0050] (1) Continue to use the above S-Cu:Co@NF as the anode.

[0051] (2) Prepare a gas diffusion cathode loaded with electro-reduced Cu: Dissolve 0.8398 g of sodium fluoride in 40 ml of deionized water and stir to form a homogeneous solution A; dissolve 2.416 g of copper nitrate trihydrate in 40 ml of deionized water and stir to form a homogeneous solution B. Then add solution B to solution A, stir for 30 min to form a blue homogeneous mixture. After shaking overnight, centrifuge and dry to obtain Cu precursor powder. Mix 10 mg of Cu precursor powder, 750 μL of isopropanol, 250 μL of deionized water, and 50 μL of Nafion binder, and ultrasonically treat for 2 h to obtain a slurry. Take 135 μL of the slurry and evenly drop it on a 1.5*1.5 cm 2 carbon paper-based gas diffusion electrode and dry it overnight at room temperature. Subsequently, perform in-situ electrochemical reduction in a flow electrolytic cell at 100 mA / cm 2 to obtain a Cu-based gas diffusion electrode, labeled as ER-Cu GDE.

[0052] (3) CO2RR-SOR co-electrolysis based on the ER-Cu GDE||S-Cu:Co@NF electrolytic cell: Assemble the ER-Cu GDE cathode and the S-Cu:Co@NF anode into a three-chamber flow cell electrolytic cell. Introduce CO2 into the gas chamber at a flow rate of 20 mL / min; 1 M KOH and 1 M K2S + 1 M KOH are used as the cathode electrolyte and the anode electrolyte respectively, and are circulated in the cathode chamber and the anode chamber through a peristaltic pump at a flow rate of 10 mL / min. Subsequently, perform CO2RR-SOR co-electrolysis in a two-electrode LSV test mode. This co-electrolysis system shows a low onset cell voltage of 0.5 V, and at a low cell voltage of 1.80 V, the co-electrolysis current density reaches 100 mA / cm 2 ( Figure 3 )

[0053] (4) CO2RR-SOR co-electrolysis for producing multi-carbon products at different current densities: Polarize the ER-Cu GDE||S-Cu:Co@NF electrolytic cell in a constant current mode to perform CO2RR-SOR co-electrolysis. Figure 4 Show the Faraday efficiencies of products such as H2, C1 (CO, HCOO-), and C 2+ (C2H4, C2H5OH, n-C3H7OH, and CH3COO-) generated at the cathode at different current densities. Among them, CO is the main C1 product, and C2H4 and C2H5OH are the main C 2+ products. As the current density increases, C 2+The Faradaic efficiency of the product gradually increases and exceeds 50% at 150 mA / cm 2 ².

[0054] Example 3: Solar-driven CO₂RR-SOR co-electrolysis for formic acid production

[0055] (1) An ER-Bi GDE||S-Cu:Co@NF electrolytic cell was used and connected in series with a commercial Si solar cell (5 * 5 cm 2 , 0.38 W) to construct a solar-driven PV-EC device for operating a CO₂RR-SOR co-electrolysis system for formic acid production. The schematic diagram is as Figure 5 shown.

[0056] (2) A xenon lamp was used to simulate sunlight illumination with an intensity of 100 mW / cm 2 ², and an ammeter was connected in series in the circuit to monitor the co-electrolysis operating current. Figure 6 As shown, this PV-EC device under illumination can obtain an operating current density of ~120 mA / cm 2 ². As the test continued, the performance of the device gradually decayed within 6 hours, and the current density slowly decreased to 100 mA / cm 2 ². The Faradaic efficiency for the production of HCOOH in the 6-hour continuous solar-driven CO₂RR-SOR co-electrolysis system remained ~95%. Polysulfides were produced in the anolyte, mainly S₂ 2- , and its concentration continuously increased with the extension of the test time. Its accumulation rate in the anolyte was 10.6 mM / h, corresponding to a degradation rate of sulfide reaching 4.12 mmol / h. The solar-to-formic acid chemical energy efficiency of this PV-EC device for CO₂RR-SOR co-electrolysis for formic acid production was calculated to be 5.8 ± 0.4%.

[0057] Example 4: Solar-driven CO₂RR-SOR co-electrolysis for multi-carbon product production

[0058] (1) An ER-Cu GDE||S-Cu:Co@NF electrolytic cell was used and connected in series with a commercial Si solar cell (5 * 5 cm 2 , 0.38 W) to construct a solar-driven PV-EC device for operating a CO₂RR-SOR co-electrolysis system for multi-carbon product production.

[0059] (2) A xenon lamp was used to simulate sunlight illumination with an intensity of 100 mW / cm 2 ², and an ammeter was connected in series in the circuit to monitor the co-electrolysis operating current. Figure 7 As shown, this PV-EC device under illumination can obtain an operating current density of ~125 mA / cm 2The operating current density, and this current density can be stable for up to 10 hours. During the 10-hour continuous solar-driven CO2RR-SOR co-electrolysis system to produce C 2+ The Faraday efficiency of the product is maintained at nearly 50%. The solar-to-chemical energy efficiency of the PV-EC device for CO2RR-SOR co-electrolysis to produce multi-carbon products and reduce CO2 to products is calculated to be 4.8%.

[0060] The continuously electrolyzed anolyte was collected and mixed with 1M HCl. A yellow precipitate was observed, centrifuged, collected, and dried to obtain solid sulfur. Figure 8 The XRD pattern of the collected sulfur is shown, corresponding to solid S8, and the inset is a photo of the sulfur.

[0061] Example 5: CO2RR-SOR co-electrolysis to produce multi-carbon products

[0062] (1) Preparation of sulfur- and nickel-codoped Co(OH)2 anode: Dissolve 0.1 mmol nickel nitrate trihydrate, 0.4 mmol cobalt nitrate hexahydrate, and 0.35 g urea in 17 mL deionized water and transfer it to a 50 mL hydrothermal autoclave with a PTFE liner. Immerse a 2*2 cm 2 nickel foam vertically into the hydrothermal solution, and then place it in an oven at 120 °C for hydrothermal treatment for 6 hours. The obtained nickel-doped Co(OH)2 electrode was washed, dried, and then immersed in a solution of 1M K2S and 1M KOH for half an hour for further sulfur doping to obtain sulfur- and nickel-codoped Co(OH)2, denoted as S-Ni:Co@NF.

[0063] (2) Preparation of a gas diffusion cathode loaded with metallic copper: Using a polytetrafluoroethylene (PTFE) membrane as the gas diffusion substrate, cut it to a size of 1.5*1.5 cm 2 . By the method of vacuum sputtering a copper target, deposit metallic copper onto the PTFE substrate. The sputtering atmosphere is Ar gas, the vacuum degree is 1.2*10 -3 Torr, the sputtering power is 50 W, and the sputtering time is 30 min. Deposit 300 nm thick copper on the PTFE substrate to obtain a PTFE-based metallic copper gas diffusion electrode, denoted as Cu / PTFE.

[0064] (3) CO₂RR-SOR Co-electrolysis Based on Cu / PTFE||S-Ni:Co@NF Electrolyzer: Assemble the Cu / PTFE cathode and S-Ni:Co@NF anode into a three-chamber flow cell electrolyzer. CO₂ is introduced into the gas chamber at a flow rate of 20 mL / min; 1 M KHCO₃ and 1 M K₂S + 1 M KOH are used as the cathode electrolyte and anode electrolyte respectively, and are circulated in the cathode chamber and anode chamber through a peristaltic pump at a flow rate of 10 mL / min. Subsequently, CO₂RR-SOR co-electrolysis is carried out in a two-electrode LSV test mode. This co-electrolysis system shows an onset cell voltage of 0.68 V. At the same time, at a low cell voltage of 2.16 V, the current density of the co-electrolysis reaches 100 mA / cm 2 , which is more energy-efficient than the conventional CO₂ electrolysis with anodic water oxidation. Polarize the Cu / PTFE||S-Cu:Co@NF electrolyzer in a constant current mode of 100 mA / cm 2 for CO₂RR-SOR co-electrolysis, and H₂, C1 (CO, HCOO - ), and C 2+ (C₂H₄, C₂H₅OH, n-C₃H₇OH, and CH₃COO - ) and other products are produced at the cathode, where C₂H₄ is the main product, and its Faraday efficiency reaches 60%.

[0065] Example 6: CO₂RR-SOR Co-electrolysis for Syngas Production

[0066] (1) Preparation of the anode of sulfur-doped Cu(OH)₂: Dissolve 0.5 mmol of copper nitrate trihydrate and 0.35 g of urea in 17 mL of deionized water, and transfer it to a 50 mL hydrothermal autoclave lined with polytetrafluoroethylene. Vertically immerse a 2*2 cm 2 nickel foam into the hydrothermal solution, and then place it in an oven at 120 °C for hydrothermal treatment for 6 hours. The obtained Cu(OH)₂ electrode is washed, dried, and then immersed in a solution of 1 M K₂S and 1 M KOH for half an hour for further sulfur doping to obtain the anode of sulfur-doped Cu(OH)₂, denoted as S-Cu@NF.

[0067] (2) Preparation of the gas diffusion cathode loaded with metallic silver: Use a polytetrafluoroethylene (PTFE) membrane as the gas diffusion substrate, cut it to a size of 1.5*1.5 cm 2 . Adopt the method of thermal evaporation deposition of Ag to deposit metallic silver onto the PTFE substrate. The vacuum degree of thermal evaporation is 1.2*10 -7 Torr, the energized current of the thermally evaporated silver particles is 0.4 A, and the deposition time is 120 min. Deposit 300 nm thick silver on the PTFE substrate to obtain the PTFE-based metallic silver gas diffusion electrode, denoted as Ag / PTFE.

[0068] (3) CO2RR-SOR co-electrolysis based on the Ag / PTFE||S-Cu@NF electrolytic cell: Assemble the Ag / PTFE cathode and S-Cu@NF anode into a three-chamber flow cell electrolytic cell. CO2 is introduced into the gas chamber at a flow rate of 20 mL / min; 1 M KHCO3 and 1 M K2S + 1 M KOH are used as the cathode electrolyte and anode electrolyte respectively, and are circulated in the cathode chamber and anode chamber through a peristaltic pump at a flow rate of 10 mL / min. Subsequently, CO2RR-SOR co-electrolysis is carried out in the two-electrode LSV test mode. This co-electrolysis system shows an onset cell voltage of 1.0 V. At the same time, at a low cell voltage of 2.5 V, the current density of the co-electrolysis reaches 100 mA / cm 2 . At 100 mA / cm 2 The Ag / PTFE||S-Cu:Co@NF electrolytic cell is polarized in the constant current mode for CO2RR-SOR co-electrolysis, and syngas mixed with H2 and CO is produced at the cathode, and the Faraday efficiency of CO reaches 70%.

[0069] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A co-electrolysis method coupling carbon dioxide reduction and sulfide oxidation, characterized in that, A flow electrolytic cell is used, with a gas diffusion electrode for carbon dioxide reduction as the cathode and a direct oxidation electrode for sulfide as the anode, to form a co-electrolysis system for carbon dioxide reduction and sulfide oxidation; during the electrolysis process, the sulfide is oxidized to a solid sulfur product; The cathode collects the carbon dioxide reduction products, and the anode collects the solid sulfur product through a series of acid treatments; The flow electrolytic cell is a three-chamber electrolytic cell, including a gas chamber, a cathode electrolyte chamber, and an anode electrolyte chamber, where the cathode electrolyte chamber and the anode electrolyte chamber are separated by a proton exchange membrane; the cathode electrolyte uses a solution of potassium hydroxide, sodium hydroxide, potassium bicarbonate, or sodium bicarbonate; the anode electrolyte uses a potassium hydroxide solution containing potassium sulfide or sodium sulfide, or a sodium hydroxide solution containing potassium sulfide or sodium sulfide; The gas diffusion electrode for carbon dioxide reduction uses a gas diffusion electrode with a gas diffusion substrate loaded with a carbon dioxide reduction electrocatalyst; the gas diffusion substrate is a hydrophobic carbon paper or polytetrafluoroethylene; the carbon dioxide reduction electrocatalyst is copper, bismuth, silver; or an alloy of any two or three phases of copper, bismuth, and silver; or an oxide of copper, bismuth, and silver; or a sulfide of copper, bismuth, and silver; The direct oxidation electrode for sulfide uses a substrate loaded with sulfur-doped metal hydroxide; the substrate is nickel foam or carbon cloth; the metal hydroxide is a metal hydroxide containing one or more of cobalt, nickel, copper, and iron; the preparation process of the sulfur-doped metal hydroxide is: soaking the electrode with the substrate loaded with the metal hydroxide in a sulfide solution to form the sulfur-doped metal hydroxide.

2. The co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation according to claim 1, wherein The process of co-electrolysis in the co-electrolysis system is: continuously introducing carbon dioxide gas into the gas chamber, and respectively introducing the cathode electrolyte and the anode electrolyte into the corresponding chambers; the cathode electrolyte and the anode electrolyte are circulated by a peristaltic pump; When applying a potential for co-electrolysis, the carbon dioxide gas on the cathode side passes through the gas diffusion electrode to form a gas-solid-liquid three-phase interface, and is reduced at this three-phase interface, while the sulfide ions on the anode side are directly oxidized on the catalyst surface to generate soluble polysulfides.

3. The co - electrolysis method for coupling carbon dioxide reduction and sulfide oxidation according to claim 2, wherein, The co-electrolysis process is powered by solar power generation, and the flow electrolytic cell is connected in series with a photovoltaic panel.

4. The co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation according to claim 1, wherein, The cathode collects the carbon dioxide reduction products including gas products and liquid products. The gas products are collected through the gas chamber outlet, and the liquid products are collected from the cathode electrolyte; the process of collecting the anode solid sulfur product is: introducing the anode electrolyte containing polysulfides into an acidic solution or gas for acid treatment to generate a precipitate, collecting the precipitate and drying it to obtain solid sulfur.

5. The co-electrolysis method for coupling carbon dioxide reduction and sulfide oxidation according to claim 4, characterized in that, The gaseous products are one or more of CO, H2, CH4, and C2H4, and the liquid products are one or more of CH3OH, HCOO - , C2H5OH, CH3COO - , n-C3H7OH.

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