Membrane-free electro-catalysis CO2 reduction decoupling water decomposition device and method

Abstract

The invention belongs to the technical field of CO2 electro-catalytic reduction, and particularly relates to a membrane-free electro-catalytic CO2 reduction decoupling water decomposition device and a membrane-free electro-catalytic CO2 reduction decoupling water decomposition method. The device comprises a left chamber electrolytic tank, a right chamber electrolytic tank and a peristaltic pump, the peristaltic pump is connected with the bottoms of the left chamber electrolytic tank and the right chamber electrolytic tank; the upper parts of the left chamber electrolytic tank and the right chamber electrolytic tank are connected through a pipeline; the left chamber electrolytic tank is provided with a CO outlet and a CO2 inlet, and the right chamber electrolytic tank is provided with an O2 outlet; an anode and a cathode are arranged in the left chamber electrolytic tank; and a cocatalyst is arranged at the bottom of the electrolytic tank in the right cavity. According to the process, CO and O2 are generated in separated electrolysis and catalysis batteries, continuous operation in a membrane-free system is supported, the ionic conductivity is improved, the internal resistance is reduced, the electrolysis efficiency is enhanced, and high-efficiency and high-speed CO2 reduction reaction can be realized in a membrane-free electrolytic bath.

Description

Technical Field

[0001] The present invention belongs to CO 2 The technical field of electrocatalytic reduction is to provide a membraneless electrocatalytic CO 2 Reduction-decoupling water splitting device and method. Background Art

[0002] Electrocatalytic CO catalysis driven by renewable energy 2 Reduction is critical to reducing greenhouse gas emissions, especially in hard-to-abate industrial sectors such as steel, cement, and ammonia production. 2 Reduction technology faces challenges, and its cost is still not competitive with traditional methods such as thermochemical methods. Therefore, there is an urgent need to improve the electrocatalytic CO 2 reduction technologies to support large-scale, low-cost production of green hydrocarbons. A promising approach to address these challenges is to optimize innovative devices and methods for electrocatalytic CO2 reduction to reduce costs while increasing current density while suppressing the competing reaction (hydrogen evolution reaction). In the past few years, electrochemical CO2 reduction electrolyzers (ECO 2 Significant progress has been made in the development of electrochemical reduction of carbon dioxide (ERCO) electrolyzers. Key factors that describe the performance of these electrolyzers include current density, Faraday efficiency, energy efficiency, and stability. Currently, there are two main types of electrochemical reduction of carbon dioxide reactors: traditional H-type reactors and membrane electrode assembly reactors (MEA-cell). The H-type electrolyzer has a high ohmic resistance due to the large distance between the anode and cathode, coupled with the influence of the ion exchange membrane and dilute electrolyte, resulting in a high cell voltage and low energy efficiency, and its current density upper limit is very low (only a few / tens of mA cm -2 ). In contrast, the membrane electrode assembly electrolyzer can be equipped with gas diffusion electrodes to make gaseous CO 2 Directly reaching the electrode surface, thereby increasing the rate of carbon dioxide reduction reaction, overcoming some of the shortcomings of the H-type electrolyzer. However, the development of membrane electrode assemblies is still limited by the price of high-performance membranes and membrane aging problems.

[0003] For example, Chinese invention patent 201980092582.1 records a reactor for the conversion of carbon dioxide, which consists of an anode chamber, a cathode chamber, an anode catalyst layer, an anode ion exchange membrane, a cathode ion exchange membrane and a cathode catalyst layer. The reactor avoids the use of an intermediate chamber and an electrolyte for ion migration by contacting the anode ion exchange membrane and the cathode ion exchange membrane, thereby reducing the energy loss of the reaction. However, this technology uses an anode ion exchange membrane and a cathode ion exchange membrane, which cannot solve the cost price of the membrane and the aging problem of the membrane. Therefore, it is necessary to develop an efficient and low-cost electrocatalytic carbon dioxide reduction reactor.

[0004] Therefore, how to provide a membrane-free, flow-type, highly efficient and clean electrocatalytic CO 2 reduction decoupled water splitting device and method is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies in the prior art, the present invention proposes a novel membrane-free device for the efficient production of CO and O 2 In this device, there is an electrochemical and chemical cycle. The cathode is used for ECO 2 RR, while the oxidation reaction at the anode is divided into two sub-reactions: electrochemical (OER) and chemical (Br - oxidation reaction). This device decouples CO 2 electrolysis, breaks through the limitations of the membrane electrolysis method, and can achieve highly efficient ECO 2 RR-coupled water splitting membrane-free electrolysis.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A membrane-free electrocatalytic CO 2 reduction decoupled water splitting device, comprising a left chamber electrolytic cell, a right chamber electrolytic cell and a peristaltic pump; the peristaltic pump is connected to the bottoms of the left chamber electrolytic cell and the right chamber electrolytic cell; the upper parts of the left chamber electrolytic cell and the right chamber electrolytic cell are connected by a pipeline;

[0008] The left chamber electrolytic cell is provided with a CO outlet and a CO 2 inlet, and the right chamber electrolytic cell is provided with an O 2 outlet;

[0009] An anode and a cathode are arranged in the left chamber electrolytic cell;

[0010] A cocatalyst is arranged at the bottom of the right chamber electrolytic cell.

[0011] Preferably, the preparation method of the cocatalyst is as follows:

[0012] a) Fe(NO 3 ) 3 ·9H 2 O, NiCl 2 ·6H 2 O and CoCl 2 ·6H 2 O are vigorously stirred and mixed in a nitric acid solution, and citric acid is continuously added as a chelating agent. After stirring at 90°C for 9 h, the mixed solution is converted into a viscous gel;

[0013] b) The viscous gel is decomposed in a tube furnace at 170 °C for 12 h, and then further heat-treated in air at 950 °C for 6 h to obtain phase-pure spinel oxide particles Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O 4 。

[0014] The beneficial effects of the above technical solution are: the cost of the cocatalyst is low, the stability is good, the redox ability is strong, and it is suitable for large-scale industrial applications.

[0015] Preferably, the anode is graphene, and the cathode is a glassy carbon sheet loaded with Ni-N-C NP / SA catalyst, and the loading amount of the Ni-N-C NP / SA catalyst is 0.05 - 0.4 mg·cm -2 。

[0016] More preferably, the loading amount of the Ni-N-C NP / SA catalyst is 0.1 mg·cm -2 。

[0017] Preferably, the preparation method of the Ni-N-C NP / SA catalyst is as follows:

[0018] 1) Mix the NiCl 2 ·6H 2 O solution with the graphene oxide suspension by stirring, continue to add 2-MI, stir at room temperature for 4 h, then centrifuge the precipitate, wash it with water and ethanol to remove the unreacted ligands, and obtain a composite material;

[0019] 2) After drying the composite material in vacuum at 50 °C for 12 h, anneal it in an N 2 atmosphere at 800 °C at a heating rate of 5 °C·min -1 for 2 h, and then wash it in 1 M hydrochloric acid for 12 h to remove large pieces of Ni, and obtain the Ni-N-C NP / SA catalyst.

[0020] The beneficial effects of the above technical solution are: the cathode catalyst Ni-N-C NP / SA of the present invention can have good electrocatalytic CO 2 reduction effect and excellent stability under neutral and acidic conditions.

[0021] Preferably, a semi-permeable chromium hydroxide layer is coated on the cathode surface.

[0022] Preferably, the electrolyte in the left chamber electrolytic cell includes a 1 - 5 M KBr solution containing 0.5 - 2 M borate buffer.

[0023] Further preferably, the electrolyte in the left chamber electrolytic cell comprises a 1 M KBr solution containing 0.7 M borate buffer.

[0024] Preferably, the electrolyte in the left chamber electrolytic cell further comprises 3 - 15 mM Na 2 Cr 2 O 7 .

[0025] Further preferably, the electrolyte in the left chamber electrolytic cell further comprises 3.8 mM Na 2 Cr 2 O 7 .

[0026] The present invention also provides a membrane-free electrocatalytic CO 2 reduction decoupled water splitting method, using the above device, comprising the following steps:

[0027] (1) Pass CO 2 into the left chamber electrolytic cell through the CO 2 inlet, set the electrolysis potential, turn on the peristaltic pump, and an electrochemical reduction of CO 2 reaction occurs at the cathode to generate CO, and the CO is discharged through the CO outlet;

[0028] (2) A bromide oxidation reaction occurs at the anode to generate bromate, and the bromate enters the right chamber electrolytic cell through the peristaltic pump, and an oxidation-reduction reaction occurs at the bottom of the right chamber electrolytic cell under the action of a co-catalyst to generate bromide and O 2 , the bromide enters the left chamber electrolytic cell through a pipeline, and O 2 is discharged through the O 2 outlet.

[0029] Preferably, the operating temperature of the right chamber electrolytic cell is 60 °C.

[0030] Preferably, the electrolysis potential is 0.7 - 1 V vs. RHE.

[0031] The technical principle of the present invention includes:

[0032] The present invention proposes an electrochemistry (CO 2 reduction and Br - oxidation) and a chemical cycle (BrO 3 - reduction and oxygen evolution reaction), dividing the oxidation reaction into two sub-reactions: electrochemistry (Br - oxidation) and chemistry (oxygen evolution reaction). The reduced Br - is oxidized in the electrochemical reaction and reacts with CO 2Reduction is complementary without generating oxygen or other volatile by-products; and, in the presence of a suitable catalyst, oxygen is spontaneously generated in the right chamber during the chemical reaction, and BrO 3 - is reduced back to its reduced state.

[0033] Br - / BrO 3 - The reversible redox potential (E 0 ) should be higher than the thermodynamic OER potential (1.23 V RHE ), and to improve efficiency, it should be oxidized at a low overpotential, ideally below the OER onset potential (the state-of-the-art OER catalyst is ~1.6 V RHE ). This indicates a reversible redox potential of ~1.4 V RHE , similar to nickel oxyhydroxide. Based on this, the bromide (Br - ) / bromate (BrO 3 - ) pair (E 0 = 1.42 V RHE ) was selected. The reduced and oxidized salts KBr and KBrO 3 have high solubility in water, 946 g·L -1 and 394 g·L -1 respectively (at 25 °C). In addition, the bromine (Br 2 ) generated at the anode is denser than water (3.1 g·cm -3 ) and is highly soluble in water (34 g·L -1 at 25 °C), which minimizes the risk of evaporation and entrainment of the CO bubbles generated at the cathode.

[0034] The present invention generates a decoupled electrolysis process for CO and O 2 in a separated cell, using Br - / BrO 3 - as a soluble redox couple for alternately storing and releasing oxygen. The electrolytic cell undergoes reaction (1) for generating CO at the cathode and reaction (2) for the anodic bromination reaction:

[0035] CO 2 + 2H + + 2e - → CO + H 2 O (1)

[0036] 2Br - → Br 2 + 2e - (2)

[0037] According to the study on the electrolysis of bromide, most of the electrolyte in which the bromine molecules (Br 2 ) generated at the anode react with water forms hypobromous acid (Reaction 3). Hypobromous acid dissociates to generate hypobromite anions (BrO - ) and protons (Reaction 4). Hypobromite anions react with hypobromous acid to generate bromate anions (Reaction 5).

[0038]

[0039] 2HBrO + BrO - → BrO 3 - + 2Br - + 2H + (5)

[0040] The entire anodic related process, Reactions 2 - 5, can be summarized as Reaction 6:

[0041] Br - + 3H 2 O → BrO 3 - + 6H + + 6e - (6)

[0042] The intermediate products HBrO and BrO - may lead to undesirable side reactions:

[0043] 6BrO - + 3H 2 O → 2BrO 3 - + 6H + + 4Br - + 1.5O 2 + 6e - (7)

[0044] HBrO + 2e - → Br - + OH - (8)

[0045] BrO - + H 2 O + 2e - → Br - + 2OH - (9)

[0046] BrO 3 - + 3H 2 O + 6e - → Br - + 6OH - (10)

[0047] BrO 3 - +2H 2 O + 4e - →BrO - + 4OH - (11)

[0048] Operating at 60 °C can inhibit oxygen evolution (Reaction 7) and achieve a bromate production efficiency close to 100% (Reaction 6). Adding a small amount of sodium dichromate (Na 2 Cr 2 O 7 ) to an aqueous solution of sodium bromide (KBr) inhibits the cathodic reverse reactions of Reactions 8 - 11. The dichromate anion (Cr 2 O 7 2- ) is reduced and deposited on the cathode, forming a semi-permeable chromium hydroxide layer on the cathode, which inhibits the cathodic loss reaction while allowing ECO 2 RR to occur unhindered. This enables high Faradaic efficiency without the need for a membrane to separate the cell into anodic and cathodic compartments.

[0049] The catalytic electrolytic cell includes columns embedded with catalysts that promote the catalytic decomposition of bromate anions (BrO 3 - ) into bromide (Br - ) and oxygen: 2BrO 3 - →2Br - + 3O 2 . Two cells are connected into a flow system to provide continuous electrolyte flow from one cell to the other.

[0050] According to the above technical solutions, compared with the prior art, the present invention provides a membrane-free electrocatalytic CO 2 reduction decoupled water splitting device and method, which has the following beneficial effects:

[0051] 1. The present invention proposes a novel membrane-free electrode assembly electrolytic cell device. This process generates CO and O 2 in separated electrolytic and catalytic cells and supports continuous operation in a membrane-free system, improving ion conductivity, reducing internal resistance, enhancing electrolysis efficiency, and enabling high-efficiency and high-rate CO 2 reduction reactions in a membrane-free electrolytic cell.

[0052] 2. The process of the present invention operates in an electrolyte close to neutral, which is different from the decoupled electrolysis of the prior art that operates in acidic or alkaline electrolytes. The present invention proposes an efficient and high-rate soluble redox coupling that supports continuous operation and isothermal processes, rather than using a nickel (oxy) hydroxide anode. Without electricity, a chemical cycle can occur spontaneously for the efficient and green production of O 2 .

[0053] 3. The present invention avoids using traditional membrane separators. The alternative design of the membrane can significantly reduce the overall cost of the system. And due to the absence of physical wear problems of the membrane, the stability and reliability of the membrane-free electrolyzer may be higher during long-term operation. Removing the membrane component simplifies the design of the electrolyzer, reducing the equipment complexity and manufacturing difficulty.

[0054] 4. The novel membrane-free electrode assembly electrolyzer device proposed by the present invention can be more closely integrated with other systems (such as renewable energy systems) to improve the overall energy utilization efficiency, providing a new solution for electrolysis technology and having broad application and development prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the provided drawings.

[0056] Figure 1 It is a schematic diagram of the device of the present invention.

[0057] Figure 2 It is the linear sweep voltammetry curve of the device of Example 1 and Comparative Example 1.

[0058] Figure 3 It is for Ni-N-C NP / SA The linear sweep voltammetry curves at different loadings of the catalyst.

[0059] Figure 4 In which a and b are the FE NP / SA of the Ni-N-C CO catalyst in KBr solutions with different concentrations and FE H2 .

[0060] Figure 5 It is the curve of the change of the conversion ratio of bromate to bromide with time at different temperatures for the device of Example 1.

[0061] Figure 6 It is for Ni-N-C NP / SALong-term catalytic stability of the catalyst in the apparatus of Example 1.

[0062] Figure 7 The conversion rates of chlorate, bromate, and iodate to chloride, bromide, and iodide.

[0063] Figure 8 Schematic diagram of the apparatus of Comparative Example 1. Detailed implementation mode

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0065] Example 1

[0066] A membrane-free electrocatalytic CO 2 reduction decoupled water splitting device, including a left chamber electrolytic cell, a right chamber electrolytic cell, and a peristaltic pump; the peristaltic pump is connected to the bottoms of the left chamber electrolytic cell and the right chamber electrolytic cell; the upper parts of the left chamber electrolytic cell and the right chamber electrolytic cell are connected by a pipeline;

[0067] The left chamber electrolytic cell is provided with a CO outlet and a CO 2 inlet, and the right chamber electrolytic cell is provided with an O 2 outlet;

[0068] An anode and a cathode are arranged in the left chamber electrolytic cell;

[0069] A co-catalyst is arranged at the bottom of the right chamber electrolytic cell.

[0070] The preparation method of the co-catalyst for redox reaction is to synthesize spinel Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O 4 :

[0071] a) 10 mmol of Fe(NO 3 ) 3 ·9H 2 O, 10 mmol of NiCl 2 ·6H 2 O, and 10 mmol of CoCl 2 ·6H 2 O are vigorously stirred and mixed in a nitric acid solution (30 ml of deionized water + 5 ml of nitric acid), and 15 mmol of citric acid is continuously added as a chelating agent. After stirring at 90 °C for 9 h, the mixed solution is converted into a viscous gel;

[0072] b) The viscous gel is decomposed in a tube furnace (with air passing through) at 170 °C for 12 h (heating rate: 10 °C·min -1 ), and then further heat-treated in air at 950 °C (heating rate: 5 °C·min -1 ) for 6 h to obtain phase-pure spinel oxide particles Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O 4 , where x1, x2, and x3 have no specific values, and the valence states of the metals in the phase-pure spinel oxide particles are a mixed value of 0 valence and oxidation valence states.

[0073] The anode is graphene, and the cathode is a glassy carbon sheet loaded with Ni-N-C NP / SA catalyst.

[0074] The loading amount of the Ni-N-C NP / SA catalyst is 0.1 mg·cm -2 .

[0075] The preparation method of the Ni-N-C NP / SA catalyst is as follows:

[0076] 1) A solution of NiCl 2 ·6H 2 O (6 mmol of NiCl 2 ·6H 2 O dissolved in 9 mL of ethanol) is stirred and mixed with a suspension of graphene oxide (15 mg) in 15 mL. Then, 0.82 g of 2-MI is added, and the mixture is stirred at room temperature for 4 h. Then, the precipitate is centrifuged and washed with water and ethanol to remove the unreacted ligands, obtaining a composite material;

[0077] 2) After the composite material is vacuum-dried at 50 °C for 12 h, it is annealed in an N 2 atmosphere at 800 °C at a heating rate of 5 °C·min -1 for 2 h, and then washed in 1 M hydrochloric acid for 12 h to remove large pieces of Ni, obtaining the Ni-N-C NP / SA catalyst.

[0078] A semi-permeable chromium hydroxide layer is coated on the surface of the cathode.

[0079] The electrolyte in the left chamber electrolytic cell includes a 1 M KBr solution containing 0.7 M borate buffer.

[0080] The electrolyte in the left chamber electrolytic cell further includes 3.8 mM Na 2 Cr 2 O 7 .

[0081] The present invention also provides a membrane-free electrocatalytic CO 2 reduction decoupled water splitting method, which uses the above device and includes the following steps:

[0082] (1) Pass CO 2 into the left chamber electrolytic cell through the CO 2 inlet, set the electrolysis potential, turn on the peristaltic pump, and an electrochemical reduction of CO 2 reaction occurs at the cathode to generate CO, and the CO is discharged through the CO outlet;

[0083] (2) At the anode, a bromide oxidation reaction occurs to generate bromate, and the bromate enters the right chamber electrolytic cell through the peristaltic pump. An oxidation-reduction reaction occurs at the bottom of the right chamber electrolytic cell under the action of a cocatalyst to generate bromide and O 2 , the bromide enters the left chamber electrolytic cell through a pipeline, and O 2 is discharged through the O 2 outlet.

[0084] The working temperature of the right chamber electrolytic cell is 60 °C.

[0085] The electrolysis potential is 0.8 V vs. RHE.

[0086] Comparative Example 1

[0087] A traditional membrane electrolysis device is used, as Figure 8 shown, which consists of three electrodes (cathode, anode, reference electrode), an electrolyte solution, an H-shaped glass container, and an ion membrane. In a 1 M KBr solution (the cathode is a glassy carbon sheet loaded with a Ni-N-C NP / SA catalyst, and the anode is graphene), an anion exchange membrane (GosuruiLian; model: Fuma FAA-PK-130) is used. Compared with the membrane-free electrolytic cell of Example 1, the H-type electrolytic cell of Comparative Example 1 only has the difference of the presence / absence of an ion membrane, and the rest are the same.

[0088] Related experiments

[0089] (1) Comparison of linear sweep voltammetry curves of the devices in Example 1 and Comparative Example 1

[0090] The membrane-free electrolytic cell device of Example 1 and the H-type electrolytic cell device of Comparative Example 1 are respectively subjected to linear sweep voltammetry (LSV), as Figure 2 shown, and the differences in the maximum current density generated can be mainly attributed to the following aspects:

[0091] Conductivity: The membrane-free electrolytic cell has better conductivity, reducing the loss in current transmission.

[0092] Ion migration freedom: The membrane-free structure allows ions to migrate faster, improving the reaction rate.

[0093] Polarization phenomenon: The membrane-free electrolytic cell can effectively reduce the polarization effect, making the current more stable.

[0094] Reaction kinetics: The reaction rate is relatively fast, enabling the effective progress of the electrochemical reaction even at high current densities.

[0095] These factors jointly contribute to the effect of the maximum current density in the membrane-free electrolytic cell of the present invention.

[0096] (2) Ni-N-C NP / SA Catalyst loading

[0097] Different concentrations of Ni-N-C (0.125, 0.25, 0.5, 1, 2, 3, 4 mg·ml NP / SA coated on a 1 cm × 1 cm glassy carbon sheet) were investigated by linear sweep voltammetry (LSV). As -1 shown, as the loading increased from 0.0125 mg·cm Figure 3 to 0.05 mg·cm -2 , the current density on the 1 cm × 1 cm area of the glassy carbon sheet was effectively increased. However, when the catalyst loading increased from 0.05 mg·cm -2 to 0.4 mg·cm -2 , there was no significant difference in the current density. This indicates that after the loading increased to 0.05 mg·cm -2 , due to the maximum local electron migration rate in the solution (affected by factors such as reactant adsorption ability, product desorption ability, and product diffusion coefficient), even if the active sites on the surface of the glassy carbon sheet increased, there would be no significant difference in the current density. Therefore, the catalyst loading ≥ 0.05 mg·cm -2 is sufficient. However, considering from an economic perspective, the optimal catalyst loading is selected as 0.1 mg·cm -2 . -2 .

[0098] (3) Concentration of KBr solution

[0099] During the production of bromate, the solution has been moving in the direction of decreasing pH, which will have a great impact on the local environment of the cathode catalyst surface. To eliminate this impact, 0.7 M borate buffer solution was added to maintain the stability of the solution pH. At the same time, with the addition of Na 2 Cr 2 O 7 , the solution will show a light yellow color. To avoid the impact of the light yellow color on the titration of bromate (and also ensure that enough chromate is deposited on the catalyst surface to protect the cathode from reducing bromate), an appropriate amount of Na 2 Cr2 O 7 (3.8 mM)

[0100] In addition, to investigate the effect of different KBr (NaBr can also be used as a Br - source) solution concentrations on the ECO 2 RR performance, the reduction products were investigated using gas chromatography (GC-8860, Agilent). Gas chromatography (GC) showed that CO and H 2 were the reduction products, and at all potentials, the total Faradaic efficiency (FE) of gaseous CO and H 2 was approximately 100%, indicating that only CO and H 2 were produced at the cathode. Figure 4 Figures a and b compare the FE of CO (FE NP / SA ) and H CO (FE 2 ) of the Ni-N-C H2 catalyst in KBr solutions with different concentrations. It is worth noting that the FE NP / SA of the Ni-N-C CO catalyst did not show a significant difference in different solutions. Therefore, a KBr solution concentration of ≥1 M is sufficient. However, from an economic perspective, the optimal concentration of the KBr solution is selected as 1 M.

[0101] (4) Reaction conditions of the electrolytic cell in the right chamber

[0102] First, potassium bromide is electrolytically oxidized through a redox reaction to obtain bromate. Then, an iodometric titration method is used to determine the concentration of bromate anions (BrO 3 - ) in the electrolyte after bromide electrolysis. In an acidic medium, bromate anions are reduced to bromide ions (Br - ) in the presence of excess iodide ions: BrO 3 - + 6I - + 3H 2 SO 4 → 3I 2 + Br - + 3SO 4 2- + 3H 2 O. The iodine (I 2 ) molecules are titrated with a standard thiosulfate solution: 2Na 2 S 2 O 3 + I 2 → 2NaI + Na 2 S 4 O 6Therefore, at the end of the electrolysis experiment, 3.8 g of KI and 40 ml of deionized aqueous solution were added to 400 μl aliquots (aliquot volume, sample to be tested) collected from the electrolytic cell (electrolytic cell volume, electrolyte = 20 ml). Then, 0.6 ml of concentrated sulfuric acid H 2 SO 4 was added, and after diluting to a volume of 50 ml with deionized water, the resulting dark purple solution was gradually titrated by adding a standardized 0.1 M sodium thiosulfate Na 2 S 2 O 3 solution (sodium thiosulfate anion concentration, C S2O3 2- = 0.1 M) until a clear solution was reached. The amount of bromate ions produced by electrolysis was calculated using the volume V S2O3 2- of the thiosulfate solution added up to this point: n BrO3 - = 1 / 6 * V 电解液 / V 待测试样 *V S2O3 2- *C S2O3 2- .

[0103] The molar concentration of the solution obtained after titrating the resulting bromate was (24 mM·L -1 ). Subsequently, the bromate was subjected to a spontaneous redox reaction at room temperature (22 °C), 30 °C, 40 °C, 50 °C, and 60 °C in a water bath at a rotation speed of 600 r / min.

[0104] Figure 5 shows the change in the proportion of bromate converted to bromide over time in a bromate solution (0.114 M·L -1 ). The conversion rate of bromate at room temperature is very small, but when the applied temperature increases in the water bath, the conversion rate of bromate rises steadily. When the temperature is applied to 60 °C, the conversion rate of bromate can reach 98% in 2 hours. Therefore, when performing the redox reaction, a temperature of ≥60 °C is sufficient. The excellent performance of the Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O 4 catalyst during the redox reaction and the successful construction of the electrolytic cell were successfully demonstrated.

[0105] (5) Test Example 1 under the following test conditions:

[0106] 1. CO 2 gas flow rate: 3 - 40 min·ml -1 ;

[0107] 2. Flow rate of peristaltic pump: 5 - 40 min·ml -1 ;

[0108] 3. Voltage range: 0.7 - 1V vs.RHE (as Figure 4 shown, within this voltage range, FE CO can be maintained above 90%).

[0109] Detect the long - term catalytic stability of the Ni - N - C NP / SA catalyst in the device of Example 1. Through gas chromatography, the Ni - N - C NP / SA catalyst was tested for the ECO 2 RR reduction product. As Figure 6 shown, within 23 hours, the Ni - N - C NP / SA catalyst maintained good stability, the CO Faraday efficiency remained at 91±2% all the time and the current density did not show obvious attenuation (10 mA·cm -2 ). Finally, after testing the bromate concentration of the liquid at one end of the redox collected by iodometry, it was found that the bromate concentration present in the solution was only 1.46 mM·L -1 .

[0110] (6) Alternative reactions for decoupling reactions

[0111] Using the device of Example 1, the difference is that the KBr solution is replaced with a KCl solution or a KI solution, and the other conditions are the same for the reaction. The conversion rates of chlorate, bromate, and iodate to chloride, bromide, and iodide are as Figure 7 shown. The reversible reduction potential of Br - / BrO 3- is E 0 = 1.42V RHE; the reversible redox potential of Cl - / ClO 3- is E 0 = 1.43V RHE; the reversible redox potential of I - / I 3- is E 0 = ~1.6V RHE. Through experiments, it was found that the redox reactions of chlorate and iodate can both be achieved by the Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O 4 catalyst. However, in I - / I 3- , I - is easily oxidized and consumes scarce iodine resources; in Cl - / ClO 3- , Cl -Low solubility, prone to cause eutrophication of water bodies, and less practical than potassium bromide. Potassium bromide has the best solubility and the lowest reversible reduction potential; meanwhile, Br - / BrO 3- has the highest reaction conversion rate. Therefore, considering comprehensively, Cl - / ClO 3- and I - / I 3- Although they can replace Br - / BrO 3- in reversible redox, they are not the optimal choice.

[0112] In summary, the present invention proposes a new DWE process that generates CO and oxygen in separate electrolytic and catalytic cells and enables continuous operation in a membrane-free system. The present invention demonstrates high efficiency and high rate in a nearly neutral electrolyte of KBr in water, where bromide is electro-oxidized to bromate in one cell while generating CO, and bromate is chemically reduced to bromide in a catalytic reaction to generate oxygen in another cell. In a 1.0 M KBr electrolyte containing 3.8 mM Na 2 Cr 2 O 7 , by covering a barrier layer on the cathode to block the electro-reduction of oxidized bromine, cathode loss reactions are prevented, and the CO Faraday efficiency remains at 91±2% throughout a 23-hour stability test. Under these conditions, there is no oxygen in the electrolytic cell, and it can operate safely without a membrane.

[0113] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A membraneless electrocatalytic CO2 reduction decoupling water splitting device, characterized in that: It comprises a left chamber electrolytic cell, a right chamber electrolytic cell and a peristaltic pump; the peristaltic pump is connected to the bottom of the left chamber electrolytic cell and the right chamber electrolytic cell; the upper parts of the left chamber electrolytic cell and the right chamber electrolytic cell are connected by a pipeline; The left chamber electrolytic cell is provided with a CO outlet and a CO2 inlet, and the right chamber electrolytic cell is provided with an O2 outlet; The left chamber electrolytic cell is provided with an anode and a cathode; A promoter is arranged at the bottom of the right chamber electrolytic cell.

2. A membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 1, characterized in that: The anode is graphene, and the cathode is loaded with Ni-NC NP / SA The Ni-NC catalyst is a glassy carbon sheet. NP / SA The catalyst loading is 0.05-0.4 mg cm -2 .

3. A membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 2, characterized in that: The Ni-NC NP / SA The preparation method of the catalyst is: 1) stirring and mixing the NiCl2·6H2O solution and the graphene oxide suspension, adding 2-MI, stirring at room temperature for 4 hours, and then centrifuging the precipitate, washing with water and ethanol to remove the unreacted ligand, and obtaining a composite material; 2) After the composite material was vacuum dried at 50 °C for 12 h, it was heated at 800 °C in a N2 atmosphere at 5 °C min -1 The Ni-NC was annealed at a heating rate of 2 h and then washed in 1 M hydrochloric acid for 12 h to remove the bulk Ni and obtain Ni-NC. NP / SA catalyst.

4. The membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 1, characterized in that: The preparation method of the co-catalyst is: a) Fe(NO3)3·9H2O, NiCl2·6H2O and CoCl2·6H2O were vigorously stirred and mixed in a nitric acid solution, and citric acid was added as a chelating agent. After stirring at 90°C for 9 hours, the mixed solution was converted into a viscous gel; b) After the viscous gel was decomposed in a tube furnace at 170 °C for 12 h and then further heat treated in air at 950 °C for 6 h, phase-pure spinel oxide particles Fe x1 Co x2 Ni x3(x1+x2+x2＝3) O4.

5. The membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 1, characterized in that: The cathode surface is coated with a semi-permeable chromium hydroxide layer.

6. The membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 1, characterized in that: The electrolyte in the left chamber electrolytic cell includes a 1-5M KBr solution containing a 0.5-2M borate buffer solution.

7. A membraneless electrocatalytic CO2 reduction decoupling water splitting device according to claim 6, characterized in that: The electrolyte in the left chamber electrolytic cell also includes 3-15 mM Na2Cr2O7.

8. A membraneless electrocatalytic CO2 reduction decoupling water splitting method, using the device according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) CO2 is introduced into the electrolytic cell in the left chamber through the CO2 inlet, the electrolysis potential is set, and the peristaltic pump is turned on. The cathode undergoes an electrochemical reduction reaction of CO2 to generate CO, which is then discharged through the CO outlet; (2) Bromide undergoes oxidation reaction at the anode to generate bromate, which enters the right chamber electrolytic cell through a peristaltic pump. At the bottom of the right chamber electrolytic cell, a redox reaction occurs under the action of a co-catalyst to generate bromide and O2, which enters the left chamber electrolytic cell through a pipeline, and O2 is discharged through the O2 outlet.

9. A membraneless electrocatalytic CO2 reduction decoupling water splitting method according to claim 8, characterized in that: The operating temperature of the right chamber electrolytic cell is 60°C.

10. The membraneless electrocatalytic CO2 reduction decoupling water splitting method according to claim 8, characterized in that: The electrolysis potential is 0.7-1 V vs. RHE.

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