A seawater electrolysis device

Abstract

The present invention discloses a seawater electrolysis device, comprising a shell, a cathode and an anode arranged in the shell, wherein the cathode and the anode are connected to a power source outside the shell to form a path; the anode is a reversible electrode having a redox cycle characteristic through a change in the valence state of an active metal, and the cathode should be an electrode material having hydrogen evolution reaction (HER) activity, which is proposed to solve the problem that in the existing direct seawater electrolysis anode half process, the chlorine evolution reaction (ClER) seriously affects the electrolysis efficiency of the oxygen evolution reaction (OER) and causes corrosion to the oxygen evolution electrode, and to solve the problem that the gas production of the anode OER and ClER of the electrolytic cell and the cathode hydrogen evolution reaction (HER) process is seriously mixed. The present invention performs the cathode HER electrode process under the premise of suppressing the anode OER and ClER half reactions in the traditional direct seawater electrolysis, so that the electrolysis step mainly produces HER, and high-purity hydrogen is produced from seawater under the condition of avoiding serious corrosion of the anode ClER.

Description

Technical Field

[0001] The invention belongs to the field of electrolysis, and in particular relates to a device for electrolyzing seawater. Background Art

[0002] "Green hydrogen" technology, which combines renewable energy power generation with water electrolysis hydrogen production technology, is expected to become the key to solving the problems of "carbon emissions" and "renewable energy consumption". Among them, offshore wind power and ocean beach photovoltaic power generation technology are important components of "green hydrogen" technology.

[0003] Among the technologies for producing hydrogen by electrolysis of water, proton exchange membrane electrolysis of water and alkaline electrolysis of water are relatively mature and have been industrialized. However, both use pure water or pure water treated with alkaline as raw materials, and there is a serious lack of fresh water resources in the working environment of offshore wind power and offshore beach photovoltaic power generation devices. This situation will directly limit the expansion of offshore wind power and solar power generation, and limit the development of "green hydrogen" technology. On the other hand, fresh water is actually a scarce resource, and pure water electrolysis will be limited by raw material costs and resource reserves in the future; seawater accounts for 96.5% of the total water reserves on the earth, which is a nearly unlimited resource. In addition, there has been a trend of increasing research on high-performance electrode materials and process technologies for direct seawater electrolysis to produce hydrogen.

[0004] Ning et al. (Materials Today Physics, 2021, 19.) reported an alkaline seawater electrolysis. Since the chlorine evolution reaction (ClER) could not be completely suppressed, the electrode showed a voltage decay of 47mV after only 100 hours of operation, which could not meet the development needs of current water electrolysis technology. Kuang et al. (Proc Natl Acad Sci USA, 2019, 116 (14): 6624-6629.) reported an alkaline simulated seawater electrolysis. The oxygen evolution electrode achieved long-term stable operation for more than 1000 hours. However, due to the construction of its metal sulfide chlorine-resistant structure, this electrode needs to be activated for more than 4 hours to achieve high-performance electrolysis, and cannot achieve rapid start and stop and adapt to the volatility of renewable energy power. In summary, the main challenge of direct seawater electrolysis technology lies in the inevitable competition between ClER and anode OER processes and the corrosion problems they bring. This is because, although the equilibrium potential of the ClER half-reaction in seawater in an alkaline environment is about 480 mV higher than that of OER, that is, ClER is more difficult to occur than OER, the inevitable local pH drop and chloride ion adsorption at high potential still lead to the occurrence of local ClER and corrosion at the anode. Therefore, although many electrode studies on seawater electrolysis have achieved remarkable results, the competitive reaction process occurring at the anode is always difficult to avoid. Summary of the invention

[0005] Based on the above background technology, the present invention proposes a seawater electrolysis device, which uses a reversible electrode with redox cycle characteristics through the change of active metal valence state as the anode, and realizes the cathode hydrogen evolution reaction (HER) with the anode OER and ClER reaction process suppressed through two-step intermittent operation of electrocatalysis and thermal reduction. This electrolysis device can effectively avoid the competition of ClER in the anode process in the seawater environment and the corrosion problems caused by it; and can directly obtain high-purity hydrogen from the device, reducing the cost consumption in the gas separation process.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A seawater electrolysis device comprises a shell, a cathode and an anode arranged in the shell, wherein the cathode and the anode are connected to a power source outside the shell to form a passage;

[0008] The anode is a reversible electrode that realizes redox cycle characteristics through the change of active metal valence state, and the cathode should be an electrode material with good HER activity.

[0009] Based on the above technical solution, preferably, the cathode is NiMoN or CoMoP loaded on nickel foam, a platinum sheet electrode, a hydrogen evolution electrode loaded with Pt / C or Ptblack catalyst porous carbon paper, etc.

[0010] Based on the above technical solution, preferably, the anode can realize the characteristics of redox cycle by changing the valence state of active metal in an alkaline seawater environment, specifically metal hydroxide, and realize reversibility through cyclic conversion between metal hydroxide / metal hydroxide oxide structure, and the metal is one or two or three of Ni, Co, Fe, Mn, Cr, V, Cu, Zn, Mo, Mg, and Al.

[0011] Based on the above technical solution, preferably, the cathode and anode electrode materials are fixed on one end of a metal rod containing a polytetrafluoroethylene coating, and the metal rod containing a polytetrafluoroethylene coating is fixedly installed on the top of the device from top to bottom and directly connected to the power supply.

[0012] Based on the above technical solution, preferably, the shell is provided with a feed port, a discharge port, an air outlet and a discharge port, and the feed port and the discharge port are controlled by a four-way valve, and the four-way valves are respectively connected to the seawater electrolysis device, the cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank;

[0013] The seawater electrolysis device is directly connected to the hydrogen storage tank via the gas outlet; and the discharge port of the seawater electrolysis device is connected to the washing water storage tank via a bypass.

[0014] Based on the above technical solution, preferably, the feed inlet of the seawater electrolysis device is located at the lower part of the device side, the discharge port is located at the upper part of the device side, the gas outlet is located at the center of the top of the device, and the discharge port is located at the center of the bottom of the device.

[0015] Based on the above technical solution, preferably, the overall structure of the seawater electrolysis device is a vertical reactor.

[0016] Based on the above technical solution, preferably, the shell of the seawater electrolysis device is sealed with a flange.

[0017] Based on the above technical solution, preferably, the seawater electrolysis device should be provided with temperature indicating control (TIC) and liquid level indicating control (LIC) detectors and instruments for feedforward control of the control valve of the device feed pipeline.

[0018] Based on the above technical solution, preferably, the seawater electrolysis device should be equipped with safety valves for venting and draining at the top and bottom, and the device venting and draining safety valves are located at the top and bottom edges of the device respectively.

[0019] Based on the above technical solutions, preferably, the whole seawater electrolysis device should use carbon steel coated with an insulating layer as the construction material; for example, the carbon steel may be Q235R.

[0020] Based on the above technical solution, preferably, the above seawater electrolysis device has the following relationship with the supporting equipment in the system:

[0021] The four-way valve is provided with a flow indicating control device, and the flow indicating control (FIC) device of the four-way valves of the feed inlet and the discharge outlet can directly perform feedforward control on the control valves of the cold seawater storage tank, the hot seawater storage tank, the washing water storage tank and the device feed pipeline;

[0022] In addition to the inlet and outlet delivery pipelines, the cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank are also provided with a bypass pipeline. The cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank are connected through the bypass pipeline. The three storage tanks (cold seawater storage tank, hot seawater storage tank, and washing water storage tank) are connected through a closed-loop flow ratio control system between each bypass to distribute the alkaline seawater circulating in the process to ensure sufficient feed reserves in each process;

[0023] The seawater electrolysis device and some of the pipelines in its system conduct heat in the form of heat exchangers, so that the waste heat in the hot seawater feed can be fully utilized.

[0024] The method for electrolyzing seawater using the seawater electrolysis device of the present invention comprises two steps:

[0025] (1) Cathode seawater electroreduction for hydrogen evolution and anodic oxidation;

[0026] (2) Anode thermal reduction: Repeat the above intermittent operation steps to produce hydrogen from seawater through multiple cycles.

[0027] Based on the above technical scheme, preferably, step (1) is "cold seawater feeding-passage-low-pressure electrolysis of seawater for hydrogen production-circuit break-washing water for gas collection", using cold seawater as a raw material, connecting the cathode, anode and power supply in the seawater electrolysis device to form a passage, controlling the electrolysis current density of the device and maintaining a certain working time; causing the cathode to undergo an electrochemical reduction reaction to convert seawater into the target product hydrogen; and causing the anode to undergo a self-oxidation reaction as a reversible auxiliary electrode, converting the metal hydroxide into a metal hydroxide oxide, thereby inhibiting the OER and ClER generated by the seawater during the anode oxidation; then disconnecting the seawater electrolysis device from the power supply, washing the device and collecting the hydrogen in this process.

[0028] Based on the above technical scheme, preferably, step (2) is "hot seawater feeding - thermal reduction auxiliary electrode - washing water rinsing"; then "cold seawater feeding", replacing hot seawater as the raw material, and maintaining a certain working time; allowing the reversible auxiliary electrode to be spontaneously reduced from metal hydroxide oxide to metal hydroxide in the hot seawater environment; at the end of the step, the device is washed, and then cold seawater is replaced as the raw material again for electrolysis, and so on, hydrogen is produced from seawater multiple times.

[0029] Based on the above technical solution, preferably, the electrolysis current density should be controlled at 10-200 mA / cm 2 .

[0030] Based on the above technical scheme, preferably, the cold seawater is natural seawater treated with alkaline substances or simulated seawater treated with alkaline substances, and the alkaline substances are potassium hydroxide (KOH), KHCO3, NaHCO3, borate or phosphate buffer, wherein the concentration of the alkaline substances is 0.1-6M and the temperature is 0-60°C.

[0031] Based on the above technical scheme, preferably, the hot seawater is natural seawater treated with alkaline substances or simulated seawater treated with alkaline substances, and the alkaline substances are potassium hydroxide (KOH), KHCO3, NaHCO3, borate or phosphate buffer, wherein the KOH concentration is 0.1-6M and the temperature is 80-100°C.

[0032] Based on the above technical solution, preferably, the simulated seawater is a solution composed of NaCl or commercial sea salt as a solute, and the NaCl concentration should be 0.4-0.6M.

[0033] Based on the above technical solution, preferably, maintaining a certain working time means that the working time of each step in the two-step intermittent operation process is 100-1000 seconds, and the operation cycles of the two steps should be kept consistent, that is, the two-step reaction is maintained for the same time.

[0034] In actual operation, the process method of the present invention preferably adopts an even number of seawater electrolysis devices working together to avoid the volatility adaptation problems and renewable energy waste problems caused by the periodicity of the two-step intermittent operation.

[0035] Beneficial Effects

[0036] 1. This method is proposed to solve the problem that ClER seriously affects the electrolysis efficiency of OER and causes corrosion to the oxygen evolution electrode in the anode half-process of the existing direct seawater electrolysis, as well as the serious mixing of gas produced by the anode OER and ClER and the cathode HER process of the electrolytic cell. Through the two-step intermittent operation of seawater electroreduction hydrogen evolution and reversible auxiliary electrode thermal reduction, the cathode HER electrode process is carried out under the premise of suppressing the anode OER and ClER half-reactions in the traditional direct seawater electrolysis, so that HER mainly occurs in the electrolysis step, and high-purity hydrogen is produced from seawater under the condition of avoiding severe corrosion of the anode ClER and HER.

[0037] 2. It can effectively avoid ClER and corrosion of the anode during direct seawater electrolysis, and improve the electrolysis efficiency and service life of the electrode material in the seawater environment.

[0038] 3. Low raw material cost, using alkaline treated seawater as direct feed, avoiding the cost burden of pretreatment process and high-value additives.

[0039] 4. The process cost is low. The OER in the electrolysis process is suppressed, so that the HER process can be carried out efficiently. The purity of the prepared hydrogen is high, which can greatly reduce the cost consumption in the gas separation process.

[0040] 5. Operating at low voltage reduces the high energy consumption of the OER four-electron process, and the electrolysis efficiency of this process method is higher than that of direct seawater electrolysis process. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a schematic diagram of the structure of a seawater electrolysis device.

[0042] In the figure: 1. device housing, 2. cathode, 3. anode, 4 and 5. metal rods with polytetrafluoroethylene coating, 6. DC power supply, 7. feed inlet, 8. discharge outlet, 9. air outlet, 10. discharge outlet.

[0043] Figure 2The potential change curves during constant current electrolysis at 100 mA for 500 seconds in an alkaline seawater environment: the blue curve is the potential change curve of the first electrolysis, and the red curve is the potential change curve of the second electrolysis after the auxiliary electrode was reduced at 95°C for 500 seconds after the first electrolysis.

[0044] Figure 3 This is the gas chromatography result of H2 gas produced after the first electrolysis at a constant current of 100 mA for 500 seconds in an alkaline seawater environment.

[0045] Figure 4 This is the gas chromatography result of H2 gas produced after the first electrolysis, the auxiliary electrode was reduced at 95℃ for 500 seconds, and then the second electrolysis was carried out at a constant current of 100 mA in an alkaline seawater environment for 500 seconds.

[0046] Figure 5 This is the gas chromatography result of O2 produced after the first electrolysis at a constant current of 100 mA for 500 seconds in an alkaline seawater environment.

[0047] Figure 6 This is the gas chromatography result of O2 produced after the first electrolysis, the auxiliary electrode was reduced at 95℃ for 500 seconds, and then the second electrolysis was carried out at a constant current of 100 mA in an alkaline seawater environment for 500 seconds.

[0048] Figure 7 It is the gas chromatography H2 standard curve.

[0049] Figure 8 This is the gas chromatography O2 standard curve.

[0050] Fig. 9 For Figure 1-6 Residual chlorine test results of alkaline seawater electrolyte after electrolysis under conditions of . DETAILED DESCRIPTION

[0051] The present invention will be further described below in conjunction with the accompanying drawings.

[0052] like Figure 1As shown, a seawater electrolysis device has an overall structure of a vertical reactor: it includes a shell 1, a cathode 2 and an anode 3 arranged in the shell, and the cathode 2 and the anode 3 are connected to a DC power supply 6 outside the shell 1 to form a passage; the device shell 1 is sealed with a flange; the cathode and anode electrode materials 2 and 3 are fixed at one end of the rod by metal rods 4 and 5 containing polytetrafluoroethylene coatings, and the rods are fixedly installed on the top of the device from top to bottom and are directly connected to the DC power supply 6; the shell is provided with a feed port 7, a discharge port 8, an air outlet 9 and a discharge port 10, the feed port 7 and the discharge port 8 are controlled by a four-way valve, and the four-way valves are respectively connected to the seawater electrolysis device, a cold seawater storage tank, a hot seawater storage tank, and a washing water storage tank; the seawater electrolysis device is directly connected to the hydrogen storage tank by the air outlet 9; the discharge port 10 of the seawater electrolysis device is connected to the washing water storage tank through a bypass. The cathode 2 should be an electrode material with good HER activity, such as NiMoN or CoMoP loaded on nickel foam, a platinum sheet electrode, a hydrogen evolution electrode loaded with Pt / C or Ptblack catalyst porous carbon paper, etc. The anode 3 is a reversible electrode, which has the characteristic of being able to realize redox cycle through the change of active metal valence state in an alkaline seawater environment, specifically a metal hydroxide, which is reversible through the cyclic conversion between metal hydroxide / metal hydroxide oxide structures, and the metal is one, two or three of Ni, Co, Fe, Mn, Cr, V, Cu, Zn, Mo, Mg, and Al.

[0053] The feed inlet 7 of the seawater electrolysis device is located at the lower part of the device side, the discharge port 8 is located at the upper part of the device side, the gas outlet 9 is located at the center of the top of the device, and the discharge port 10 is located at the center of the bottom of the device;

[0054] The seawater electrolysis device should be equipped with temperature indicating control (TIC) and liquid level indicating control (LIC) detectors and instruments to perform feedforward control on the control valve of the device feed pipeline;

[0055] The seawater electrolysis device should be equipped with safety valves for venting and draining at the top and bottom. The safety valves for venting and draining the device should be located at the top and bottom edges of the device respectively;

[0056] The whole seawater electrolysis device should be constructed of Q235R carbon steel coated with an insulating layer;

[0057] The above-mentioned seawater electrolysis device has the following relationship with the supporting equipment in the system:

[0058] The flow indicator control (FIC) equipment of the four-way valves of the feed and discharge ports can directly perform feedforward control on the control valves of the cold seawater storage tank, hot seawater storage tank, washing water storage tank and the device feed pipeline;

[0059] In addition to the inlet and outlet pipelines, the cold seawater storage tank, hot seawater storage tank, and washing water storage tank are equipped with bypass pipelines. The three tanks are connected through a closed-loop flow ratio control system to distribute the alkaline seawater circulating in the process to ensure sufficient feed reserves in each process.

[0060] The seawater electrolysis device and some of the pipes in its system conduct heat in the form of heat exchangers, so that the waste heat in the hot seawater feed can be fully utilized;

[0061] The process method of the present invention adopts an even number of seawater electrolysis devices working together in actual operation, thereby avoiding the fluctuation adaptation problem and renewable energy waste problem caused by the periodicity of the two-step intermittent operation.

[0062] Based on the above device, the specific operation steps of the present application method are as follows:

[0063] Cold seawater feeding: The cold seawater is seawater or simulated seawater treated with potassium hydroxide (KOH) alkalinity, and the KOH concentration is 0.1-6M, and the temperature is 0-60°C; in this step, the cold seawater enters the seawater electrolysis device from the cold seawater storage tank through the feed port 7, and the feed amount is 50-80% of the device volume;

[0064] Passage: The cathode and anode electrodes 2, 3 in the seawater electrolysis device are connected to the power source 6 through the polytetrafluoroethylene-coated metal rods 4, 5 to form a passage;

[0065] Low current electrolysis of seawater to produce hydrogen: control device at 10-200mA / cm 2 Electrolysis is performed at a current density of 100-1000 seconds, and intermittent operation is maintained for 100-1000 seconds, so that the cathode 2 undergoes an electrochemical reduction reaction to convert seawater into the target product hydrogen; the anode 3 acts as a reversible auxiliary electrode to undergo an oxidation reaction to convert metal hydroxide into metal hydroxide oxide, and the Faraday efficiency of the oxidation reaction is relatively high, so the occurrence of anode electrocatalytic OER and ClER in this step is largely suppressed; a portion of the hydrogen generated that is not absorbed by the seawater feed goes to the hydrogen storage tank from the gas outlet 9 of the device;

[0066] Disconnection: disconnect the cathode and anode electrodes 2 and 3 in the seawater electrolysis device from the DC power supply 6;

[0067] Washing water gas collection: the washing water is natural seawater or simulated seawater after alkaline treatment with potassium hydroxide (KOH), the KOH concentration is 0.1-6M, and the temperature is 0-60°C; in this step, the washing water enters the seawater electrolysis device from the washing water storage tank through the feed port 7, and the feed amount is 200-500% of the device volume, ensuring that the remaining gas products are completely sent to the cold seawater storage tank together with the cold seawater and the washing water through the discharge port 8; desorb and collect hydrogen in the cold seawater storage tank; then, the remaining washing water in the device returns to the washing water storage tank through the device discharge port 10 through a bypass for standby use;

[0068] Hot seawater feed: The hot seawater is natural seawater or simulated seawater treated with potassium hydroxide (KOH) alkalinity, the KOH concentration is 0.1-6M, and the temperature is 80-100°C; in this step, the hot seawater enters the seawater electrolysis device from the hot seawater storage tank through the feed port 7, and the feed amount is 50-80% of the device volume;

[0069] Thermal reduction auxiliary electrode: the electrode material is kept in a hot seawater environment for the same intermittent operation time (100-1000 seconds) as in the low-pressure electrolysis of seawater for hydrogen production, so that the reversible auxiliary electrode 3 is spontaneously reduced from the metal hydroxide oxide to the metal hydroxide in the hot seawater environment;

[0070] Washing water flushing: The washing water is natural seawater or simulated seawater after alkaline treatment with potassium hydroxide (KOH), and its KOH concentration is 0.1-6M and its temperature is 0-60°C; in this step, the washing water enters the seawater electrolysis device from the washing water storage tank through the feed port 7, and the feed amount is 200-500% of the volume of the device, and goes to the hot seawater storage tank through the discharge port 8, and ensures that the oxygen generated in the thermal reduction auxiliary electrode process can be completely released and removed; then, the residual washing water in the device returns to the washing water storage tank through the bypass 10 for standby use.

[0071] In the present application, cold seawater and hot seawater can be directly and continuously introduced into the seawater of the required temperature, or the electrolysis device as a whole is placed in an environment of the required temperature to ensure that the seawater reaches the required temperature, without too much restriction. The following is a specific embodiment of the electrolysis method to illustrate the technical effect of the present invention by regulating the temperature of the alkaline simulated seawater in a water bath and then regulating the alkaline cold seawater or hot seawater feed of the seawater electrolysis device.

[0072] In this embodiment, the material of the hydrogen evolution electrode, i.e., the cathode, of the seawater electrolysis device is a 2*2 cm Pt sheet electrode, and the material of the reversible auxiliary electrode, i.e., the anode, is a 2*3 cm nickel foam electrode directly grown with nickel-cobalt layered double hydroxides (NiCo LDHs) (prepared with reference to the literature: Bifunctional Heterostructure Assembly of NiFe LDH Nanosheetson NiCoP Nanowires for Highly Efficient and Stable Overall Water Splitting. Advanced Functional Materials, 2018, 28(14).); the electrolysis raw material is alkaline simulated seawater, in which the concentration of KOH is 1 M and the concentration of NaCl is 0.5 M;

[0073] (1) alkaline cold simulated seawater is introduced into a seawater electrolysis device, and the cathode, anode and direct current power supply in the electrolysis device are connected to form a circuit. The device is operated in a constant temperature water bath at 15°C to use alkaline simulated cold seawater as a raw material, and the alkaline simulated seawater is electrolyzed at a constant current of 100 mA. At this time, the electrolysis potential of the electrolysis device is about 1.8 V, and is maintained for 500 seconds, so that the alkaline simulated seawater undergoes an electrochemical reduction reaction at the cathode to release hydrogen, and the anode, as a reversible auxiliary electrode, undergoes an oxidation reaction itself, and the metal hydroxide is converted into a metal hydroxide oxide. This step is the electrolysis process;

[0074] (2) collecting hydrogen from the sealed seawater electrolysis device during the electrolysis process, and passing the gas generated by the device at any stage during the electrolysis process into a hydrogen and oxygen phase chromatography to test its composition; then, disconnecting the seawater electrolysis device from the DC power supply;

[0075] (3) taking out the reversible auxiliary electrode and placing the device in a 95°C constant temperature water bath to raise the electrolyte temperature to 95°C, that is, using alkaline hot seawater as the raw material, and then placing the reversible auxiliary electrode in the seawater electrolysis device and keeping it for 500 seconds, so that the reversible auxiliary electrode is spontaneously reduced from metal hydroxide oxide to metal hydroxide in the alkaline thermal simulated seawater environment, and oxygen is generated during the thermal reduction of the auxiliary electrode. This step is the spontaneous reduction process of the reversible auxiliary electrode;

[0076] (4) Remove the reversible auxiliary electrode and place the seawater electrolysis device in a constant temperature water bath at 15°C;

[0077] (5) Repeat steps (1) to (4) once to perform a second seawater electrolysis operation.

[0078] like Figure 2As shown in the figure, in the first and second steps of electrolyzing seawater to produce hydrogen (electrolyzing alkaline cold simulated seawater at a constant current of 100 mA for 500 seconds), the potential can be basically kept stable within 500 seconds; the electrolysis potential is about 1.8 V. The reason why the performance of the second electrolysis of seawater is improved compared with the first electrolysis is that the reversible auxiliary electrode is reduced after the first electrolysis to activate the anode, that is, the conversion process of metal hydroxide / metal oxyhydroxide is faster, resulting in a lower reaction overpotential;

[0079] like Figure 3 As shown, in the first electrolysis of seawater (electrolysis of alkaline cold simulated seawater at 100 mA for 500 seconds), the chromatographic peak of H2 in the produced gas is a complete single peak, proving that the product of seawater electrolysis is high-purity H2;

[0080] like Figure 4 As shown, in the second electrolysis of seawater (after the first electrolysis of alkaline cold simulated seawater, the device was placed in a 95°C constant temperature water bath for reduction of the reversible auxiliary electrode, the electrolyte was heated to 95°C and maintained for 500 seconds, then taken out and cooled to room temperature. Then it was placed in a 15°C constant temperature water bath at 100 mA for 500 seconds to electrolyze alkaline cold simulated seawater for the second electrolysis), the chromatographic peak of H2 in the produced gas was a complete single peak, proving that the product of seawater electrolysis was high-purity H2;

[0081] like Figure 5 As shown, in the first electrolysis of seawater (constant current electrolysis of alkaline cold simulated seawater at 100 mA for 500 seconds), the concentration of O2 in the produced gas was about 7764.1 ppm, that is, the content of O2 in the produced gas was about 0.77641%, proving that the OER process was effectively suppressed;

[0082] like Figure 6 As shown, the second electrolysis of seawater (after the first electrolysis, the device was placed in a 95°C constant temperature water bath for reduction of the reversible auxiliary electrode, the electrolyte was heated to 95°C and maintained for 500 seconds, then taken out and cooled to room temperature. It was then placed in a 15°C constant temperature water bath and electrolyzed alkaline simulated seawater at a constant current of 100 mA for 500 seconds), the concentration of O2 in the gas production was about 19042.7ppm, that is, the content of O2 in the gas production was still less than 2%, compared with the oxygen evolution Faraday efficiency of direct seawater electrolysis, the OER process was still effectively suppressed;

[0083] Figure 3 , Figure 4 The gas chromatography results in Figure 7 The H2 standard curve of gas chromatography is obtained. Figure 5 , Figure 6 The gas chromatography results in Figure 8 Derived from the O2 standard curve of gas chromatography;

[0084] like Fig. 9 As shown, the alkaline simulated seawater electrolyte after the above two electrolysis processes of seawater was tested for residual chlorine. The residual chlorine test paper showed that no chlorine gas or hypochlorite was generated in the electrolyte, and this was also proved by the fact that no color change of the starch indicator occurred after adding excess NaI.

Claims

1. A seawater electrolysis device, characterized in that: It includes a shell, a cathode and an anode arranged in the shell, and the cathode and the anode are connected to a power source outside the shell to form a passage; The anode is a reversible electrode having redox cycle characteristics through changes in the valence state of the active metal, and the cathode should be an electrode material having HER activity; The reversible electrode is a metal hydroxide, and the metal of the metal hydroxide is a Ni and Co bimetallic; The method of electrolyzing seawater by a seawater electrolysis device includes two steps: (1) Cathode seawater electroreduction for hydrogen evolution and anodic oxidation; (2) anode thermal reduction; repeating the above intermittent operation steps to produce hydrogen from seawater through multiple cycles; The working time of each step in the two-step intermittent operation process is 100-1000 seconds, and the operation cycles of the two steps should be consistent; An operation mode in which an even number of seawater electrolysis devices work together; Step (1) is "cold seawater feeding-passage-low-pressure electrolysis of seawater for hydrogen production-circuit breaking-washing water for gas collection". Cold seawater is used as a raw material, and a cathode, an anode and a power source in the seawater electrolysis device are connected to form a passage, and the electrolysis current density of the device is controlled and maintained for a certain working time; the cathode undergoes an electrochemical reduction reaction to convert the seawater into the target product hydrogen; and the anode, as a reversible auxiliary electrode, undergoes a self-oxidation reaction to convert the metal hydroxide into a metal hydroxide oxide, thereby inhibiting the OER and ClER generated by the seawater during the anode oxidation; then the seawater electrolysis device is disconnected from the power source, and the device is washed and the hydrogen in this process is collected; Step (2) is "hot seawater feeding - thermal reduction auxiliary electrode - washing water washing"; then "cold seawater feeding", replacing hot seawater as the raw material and maintaining a certain working time; allowing the reversible auxiliary electrode to be spontaneously reduced from metal hydroxide oxide to metal hydroxide in the hot seawater environment; at the end of the step, the device is washed, and then cold seawater is replaced as the raw material for electrolysis, and so on, hydrogen is produced from seawater multiple times; The electrolysis current density is controlled at 10-200 mA / cm 2 .

2. The seawater electrolysis device according to claim 1, characterized in that: The cathode and anode electrode materials are fixed on one end of a metal rod with a polytetrafluoro coating. The metal rod with a polytetrafluoro coating is fixedly installed on the top of the device from top to bottom and is directly connected to a power source.

3. The seawater electrolysis device according to claim 1, characterized in that: The shell is provided with a feed inlet, a feed outlet, a gas outlet and a discharge port. The feed inlet and the discharge port are controlled by a four-way valve, and the four-way valves are respectively connected to the seawater electrolysis device, the cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank; the gas outlet of the seawater electrolysis device is connected to the hydrogen storage tank; and the discharge port of the seawater electrolysis device is connected to the washing water storage tank.

4. The seawater electrolysis device according to claim 1, characterized in that: The feed inlet of the seawater electrolysis device is located at the lower part of the device side, the discharge port is located at the upper part of the device side, the gas outlet is located at the center of the top of the device, and the discharge port is located at the center of the bottom of the device.

5. The seawater electrolysis device according to claim 1, characterized in that: The seawater electrolysis device should be provided with detectors or instruments for temperature indication control and liquid level indication control.

6. The seawater electrolysis device according to claim 1, characterized in that: Safety valves are provided at the top and bottom of the seawater electrolysis device.

7. The seawater electrolysis device according to claim 1, characterized in that: The overall structure of the seawater electrolysis device is a vertical reactor.

8. The seawater electrolysis device according to claim 1, characterized in that: The shell of the seawater electrolysis device is sealed by a flange.

9. The seawater electrolysis device according to claim 3, characterized in that: The four-way valve is provided with a flow indicating control device; in addition to the inlet and outlet delivery pipelines, a bypass pipeline is also provided between the cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank, and the cold seawater storage tank, the hot seawater storage tank, and the washing water storage tank are connected through the bypass pipeline.

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