Method for producing hydrogen and extracting lithium from seawater and application thereof

Abstract

The application discloses a method for hydrogen production and lithium extraction from seawater and application thereof, and belongs to the technical field of seawater resource utilization. 2+ and Li + A lithium-magnesium layered double hydroxide protective layer is generated in situ on the surface of the cathode, lithium extraction and chlorine blocking are simultaneously realized, after lithium extraction by a weak acid, deep magnesium removal, and electrochemical hydrogenation of the lithium-rich liquid, lithium hydride is prepared, and the by-product is recycled. The application adopts the method for hydrogen production and lithium extraction from seawater and application thereof, and through deep cooperation of hydrogen production and lithium extraction, a lithium-magnesium layered double hydroxide protective layer is generated in the gradient alkali microzone formed in situ in the cathode hydrogen evolution reaction, the protective layer simultaneously realizes multiple functions of high-selectivity lithium extraction, high-efficiency physical chlorine ion blocking and electrode corrosion resistance, and further, the lithium extraction product is directly electrochemically hydrogenated to prepare high-value-added lithium hydride.

Description

Technical Field

[0001] This invention relates to the field of seawater resource utilization technology, and in particular to a method for producing hydrogen and extracting lithium from seawater and its application. Background Technology

[0002] Seawater accounts for 96.5% of the Earth's water resources, making it an ideal source of hydrogen energy. Direct electrolysis of seawater to produce hydrogen avoids the consumption of freshwater resources and has broad application prospects. However, direct electrolysis of seawater to produce hydrogen faces two major technical challenges: one is the high concentration of chloride ions (Cl-) in seawater. - At approximately 19,500 ppm, a chlorine evolution side reaction (2Cl₂) will occur at the anode. - →Cl2+2e - This not only reduces hydrogen production efficiency but also severely corrodes the electrodes, leading to a significant shortening of equipment lifespan; secondly, seawater contains a large number of impurities such as magnesium and calcium ions, which easily form hydroxide precipitates in the alkaline environment of the cathode, clogging the diaphragm and electrodes and further deteriorating the electrolysis process.

[0003] Meanwhile, seawater contains approximately 230 billion tons of lithium resources, thousands of times greater than onshore lithium reserves. Lithium is a key raw material for new energy vehicles, energy storage batteries, and other fields, possessing extremely high strategic value. However, the lithium concentration in seawater is extremely low (only about 0.17 ppm), and it coexists with large amounts of sodium, magnesium, and calcium ions, especially with a Mg / Li mass ratio as high as several thousand, making selective lithium extraction extremely difficult.

[0004] Existing seawater lithium extraction technologies mainly include adsorption methods (such as aluminum-based adsorbents and manganese oxide ion sieves), membrane separation methods, and electrochemical intercalation methods. However, these methods generally suffer from problems such as low adsorption capacity, poor selectivity, the need to add a large amount of chemicals to adjust pH, and high energy consumption. Moreover, most of them are independent of the seawater hydrogen production process and cannot achieve the synergistic utilization of energy and materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing hydrogen and extracting lithium from seawater and its application. Through deep synergy between hydrogen production and lithium extraction, a lithium-magnesium layered double hydroxide protective layer is generated in the gradient alkaline micro-region formed in situ during the cathode hydrogen evolution reaction. This protective layer simultaneously achieves multiple functions, including highly selective lithium extraction, efficient physical barrier against chloride ions, and resistance to electrode corrosion. Furthermore, the lithium extraction product is directly electrochemically hydrogenated to prepare high-value-added lithium hydride. At the same time, the byproducts dilute hydrochloric acid, regenerated adsorbent materials, and unreacted hydrogen are all recycled in a closed loop. This significantly improves the stability of seawater hydrogen production and the efficiency of lithium resource recovery while reducing chemical and energy consumption, realizing the integrated, clean, and high-value utilization of seawater resources.

[0006] To achieve the above objectives, the present invention provides a method for producing hydrogen and extracting lithium from seawater, comprising the following steps: S1. Construct a three-chamber electrolytic cell, in which the cathode chamber and the intermediate chamber are separated by a cation exchange membrane, and the intermediate chamber and the anode chamber are separated by a dense cation exchange membrane or an anion blocking membrane. S2, Injecting Mg-containing... 2+ An alkaline electrolyte containing nano-Mg(OH)2 seed crystals is introduced into the intermediate chamber, pretreated seawater is introduced into the anode chamber, and an inert electrolyte is injected into the anode chamber for electrolysis. S3, utilizing the OH generated by the cathode hydrogen evolution reaction - The formation of gradient alkaline microregions allows Mg migrating from seawater to... 2+ and Li + A lithium-magnesium layered double hydroxide protective layer was generated in situ on the cathode surface, while Li was extracted. + And block Cl - ; S4. Treat the lithium-magnesium layered double hydroxide protective layer obtained in S3 with a weakly acidic buffer solution to selectively remove Li. + The lithium-rich solution and regenerated LDH are obtained, and the lithium-rich solution is subjected to deep magnesium removal to obtain a magnesium-removed lithium-rich solution. S5. Under anhydrous and oxygen-free conditions, the magnesium-free lithium-rich solution obtained in S4 is subjected to an electrochemical hydrogenation reaction by introducing hydrogen gas with a gas diffusion electrode as the cathode to generate lithium hydride. The unreacted hydrogen gas is recycled to the hydrogen inlet, and the lithium hydride is separated, washed, and dried under anhydrous and oxygen-free conditions.

[0007] Preferably, in S2, seawater pretreatment includes microfiltration and adjusting the pH to 7.5-8.0 with dilute hydrochloric acid, which is derived from a byproduct generated at the diaphragm between the anode chamber and the intermediate chamber in S1.

[0008] Preferably, in S3, the gradient alkali micro-region is controlled by setting the initial pH of the cathode chamber to 10-11 and the current density to 50-150 mA / cm². 2 This achieves a local pH ≥ 12 on the electrode surface, while the pH ≤ 10.5 is achieved at locations far from the electrode.

[0009] Preferably, in S3, the thickness of the lithium-magnesium layered double hydroxide protective layer is 100 nm-2 μm, and the specific surface area is >50 m². 2 / g, for Cl - The barrier efficiency is ≥99%.

[0010] Preferably, in S4, the weakly acidic buffer is one of citrate-sodium citrate buffer, acetic acid-ammonium acetate buffer, or formic acid-sodium formate buffer, with a pH range of 5.0-6.5.

[0011] Preferably, in S4, deep magnesium removal is performed using chelating resin adsorption or carbonate / phosphate precipitation.

[0012] Preferably, in S5, the conditions for the electrochemical hydrogenation reaction are: current density 5-20 mA / cm². 2 Hydrogen pressure 0.1-0.5MPa, temperature 20-40℃, electrolyte water content <1000ppm.

[0013] This invention also provides an application for seawater hydrogen production and lithium extraction, applying the above-described method for seawater hydrogen production and lithium extraction to the preparation of hydrogen storage materials, solid electrolytes, or organic synthesis reducing agents.

[0014] Therefore, the present invention, employing the above-mentioned method for producing hydrogen and extracting lithium from seawater and its application, has the following beneficial effects: (1) Utilizing the OH generated in situ by the cathode hydrogen evolution reaction - A gradient alkaline microregion is formed (electrode surface pH ≥ 12, bulk pH ≈ 10.5). This gradient environment cannot be achieved by adding an external alkaline agent, thus preventing the rapid aggregation and precipitation of Mg(OH)2. 2+ and Li + A dense lithium-magnesium layered double hydroxide (Li-Mg-LDH) protective layer is directionally grown on the electrode surface, resulting in a lithium enrichment factor of up to 3120 times, which is far superior to the traditional adsorption method (usually <100 times), and achieves ultra-high selectivity extraction of lithium from seawater.

[0015] (2) The lithium extraction product provides feedback protection to the hydrogen production process: the in-situ generated Li-Mg-LDH protective layer also serves as a physical barrier against chloride ion corrosion, protecting Cl... - With a barrier rate ≥99%, the Cl in the anode chamber is able to achieve a high barrier efficiency. - With a concentration below 5 ppm, the side reaction of chlorine evolution and electrode corrosion are completely avoided, and the electrode life exceeds 2000 hours, which is more than 500 times that of Comparative Example 1 (without LDH layer), greatly improving the stability and economy of seawater hydrogen production.

[0016] (3) A strong coupling and closed-loop system of hydrogen production, lithium extraction, and hydride preparation are achieved: each step has an inseparable synergistic relationship: if hydrogen production is stopped, there is no gradient alkaline microregion, the lithium extraction efficiency drops by 90% and the electrode corrodes rapidly; if lithium extraction is stopped, there is no LDH protective layer, and chloride ions penetrate and cause chlorine evolution; if strong acid is used for delithiation, the LDH structure is irreversibly destroyed. In addition, the by-product dilute hydrochloric acid is recycled for seawater pretreatment, the regenerated LDH is recycled back to the lithium extraction step, and the unreacted hydrogen is recycled for the electrochemical hydrogenation step, reducing the dependence on external chemicals by more than 90%.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1This invention relates to a method for producing hydrogen and extracting lithium from seawater, and its applications in Examples 1-4 and Comparative Examples 1-3, showing the lithium enrichment factor and Cl... - The results of the barrier rate test are shown in the figure. Figure 1 Figure (a) shows the lithium enrichment factor test results for Examples 1-4 and Comparative Examples 1-3. Figure 1 (b) in the text refers to Cl from Examples 1-4 and Comparative Examples 1-3. - Barrier rate test results graph; Figure 2 The graph shows the Faraday efficiency and lithium hydride yield test results of the seawater hydrogen production and lithium extraction method of the present invention and its application examples 1-4 and comparative examples 1-3. Figure 3 This invention relates to a method for producing hydrogen and extracting lithium from seawater, and its applications in Examples 1-4 and Comparative Examples 1-3. + Desorption rate, Mg 2+ The dissolution rate test results are shown in the figure. Figure 3 (a) in the text refers to Li from Examples 1-4 and Comparative Examples 1-3. + Desorption rate test results graph Figure 3 (b) in the text refers to Mg from Examples 1-4 and Comparative Examples 1-3. 2+ Dissolution rate test results graph. Detailed Implementation

[0019] This invention provides a method for producing hydrogen and extracting lithium from seawater, comprising the following steps: S1. Construct a three-chamber electrolytic cell, in which the cathode chamber and the intermediate chamber are separated by a cation exchange membrane, and the intermediate chamber and the anode chamber are separated by a dense cation exchange membrane or an anion blocking membrane. S2, Injecting Mg-containing... 2+ An alkaline electrolyte containing nano-Mg(OH)2 seed crystals is introduced into the intermediate chamber, pretreated seawater is introduced into the anode chamber, and an inert electrolyte is injected into the anode chamber for electrolysis. S3, utilizing the OH generated by the cathode hydrogen evolution reaction - The formation of gradient alkaline microregions allows Mg migrating from seawater to... 2+ and Li + A lithium-magnesium layered double hydroxide protective layer was generated in situ on the cathode surface, while Li was extracted. + And block Cl - ; S4. Treat the lithium-magnesium layered double hydroxide protective layer obtained in S3 with a weakly acidic buffer solution to selectively remove Li. + The lithium-rich solution and regenerated LDH are obtained, and the lithium-rich solution is subjected to deep magnesium removal to obtain a magnesium-removed lithium-rich solution. S5. Under anhydrous and oxygen-free conditions, the magnesium-free lithium-rich solution obtained in S4 is subjected to an electrochemical hydrogenation reaction by introducing hydrogen gas with a gas diffusion electrode as the cathode to generate lithium hydride. The unreacted hydrogen gas is recycled to the hydrogen inlet, and the lithium hydride is separated, washed, and dried under anhydrous and oxygen-free conditions.

[0020] In this invention, in S2, seawater pretreatment includes microfiltration and adjusting the pH to 7.5-8.0 with dilute hydrochloric acid, which is derived from a byproduct generated at the diaphragm between the anode chamber and the intermediate chamber in S1.

[0021] In this invention, in S3, the gradient alkaline micro-region is controlled by setting the initial pH of the cathode chamber to 10-11 and the current density to 50-150 mA / cm². 2 This achieves a local pH ≥ 12 on the electrode surface, while the pH ≤ 10.5 is achieved at locations far from the electrode.

[0022] In this invention, in S3, the thickness of the lithium-magnesium layered double hydroxide protective layer is 100 nm-2 μm, and the specific surface area is >50 m². 2 / g, for Cl - The barrier efficiency is ≥99%.

[0023] In this invention, in S4, the weakly acidic buffer solution is one of citrate-sodium citrate buffer, acetic acid-ammonium acetate buffer, or formic acid-sodium formate buffer, with a pH range of 5.0-6.5.

[0024] In this invention, in S4, deep magnesium removal is performed using chelating resin adsorption or carbonate / phosphate precipitation.

[0025] In this invention, the conditions for the electrochemical hydrogenation reaction in S5 are: current density 5-20 mA / cm². 2 Hydrogen pressure 0.1-0.5MPa, temperature 20-40℃, electrolyte water content <1000ppm.

[0026] This invention also provides an application for seawater hydrogen production and lithium extraction, applying the above-described method for seawater hydrogen production and lithium extraction to the preparation of hydrogen storage materials, solid electrolytes, or organic synthesis reducing agents.

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims and are all within the protection scope of the present invention.

[0028] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The term "embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment, nor does it specifically limit its independence or connection with other embodiments. In principle, in this application, as long as there are no technical contradictions or conflicts, the technical features mentioned in each embodiment can be combined in any way to form corresponding implementable technical solutions.

[0029] Unless otherwise defined, the technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the use of related terms herein is merely for the purpose of describing particular embodiments and is not intended to limit this application.

[0030] In this invention, unless otherwise specified, all other test materials and instruments are conventional test materials in the field and can be purchased through commercial channels.

[0031] Example 1 This invention provides a method for producing hydrogen and extracting lithium from seawater, comprising the following steps: S1. Construct a three-chamber electrolytic cell, with the cathode chamber and the middle chamber separated by a cation exchange membrane Nafion 117, and the middle chamber and the anode chamber separated by a Neosepta ACS membrane. The anode is IrO2 / Ti.

[0032] S2, Injecting Mg-containing... 2+ An alkaline electrolyte containing nano-Mg(OH)2 seed crystals is introduced into the intermediate chamber, pretreated seawater is introduced into the anode chamber, and an inert electrolyte is injected into the anode chamber for electrolysis. Seawater was microfiltered at 0.45 μm and the pH was adjusted to 7.8 using dilute hydrochloric acid as a byproduct. The cathode electrolyte consisted of 100 mL of 0.1 M KOH + 0.01 M MgCl2 + 0.5 g / L nano-Mg(OH)2 seed crystals, with a pH of 10.5. The anode electrolyte was 0.5 M Na2SO4, and the seawater flow rate in the intermediate chamber was 1.5 mL / min.

[0033] S3, utilizing the OH generated by the cathode hydrogen evolution reaction - The formation of gradient alkaline microregions allows Mg migrating from seawater to... 2+ and Li + A lithium-magnesium layered double hydroxide (Li-Mg-LDH) protective layer was generated in situ on the cathode surface, while Li was extracted. + And block Cl - ; Current density 100mA / cm 2Electrolysis was performed at 35℃ for 24 hours. Gradient alkaline microregions formed, and a Li-Mg-LDH protective layer (approximately 500 nm thick, with a specific surface area of ​​62 m²) was formed on the cathode surface. 2 / g). Hydrogen production rate 560 mL / cm² 2 •h, Faraday efficiency 94%. Anode chamber Cl - Concentration <5ppm, barrier rate 99.5%.

[0034] S4. Treat the lithium-magnesium layered double hydroxide protective layer obtained in S3 with a weakly acidic buffer solution to selectively remove Li. + The lithium-rich solution and regenerated LDH are obtained, and the lithium-rich solution is subjected to deep magnesium removal to obtain a magnesium-removed lithium-rich solution. The lithium removal solution was a 0.1M citrate-sodium citrate buffer (pH=5.5), with a solid-liquid ratio of 1:20 (g / mL), and stirred for 30 minutes. Lithium-rich solution: Li + 1850ppm, Mg 2+ 72 ppm (Mg dissolution rate 4.1%). Deep magnesium removal: The effluent was passed through an Amberlite IRC748 chelating resin column (flow rate 2 mL / min), and the Mg content was... 2+ <0.1ppm, Mg / Li molar ratio <5×10 -5 Concentrate to Li under reduced pressure + 2.2M, water content 750ppm.

[0035] S5. Under anhydrous and oxygen-free conditions, the magnesium-free lithium-rich solution obtained in S4 is subjected to an electrochemical hydrogenation reaction by introducing hydrogen gas with a gas diffusion electrode as the cathode to generate lithium hydride. The unreacted hydrogen gas is recycled to the hydrogen inlet, and the lithium hydride is separated, washed, and dried under anhydrous and oxygen-free conditions.

[0036] Gas diffusion electrode (carbon paper loaded with Ru 1 mg / cm³) 2 H2 pressure 0.2 MPa, current density 10 mA / cm² 2 6 hours at room temperature.

[0037] Example 2 The only difference between this embodiment and Embodiment 1 is that the current density in S3 is changed to 80 mA / cm². 2 All other conditions are the same.

[0038] Example 3 The only difference between this embodiment and Example 1 is that the lithium removal solution in S4 is replaced with 0.1M acetate-ammonium acetate buffer (pH=5.8), while all other conditions are the same.

[0039] Example 4 The only difference between this embodiment and Example 1 is that the deep magnesium removal in S4 is changed to a precipitation method: 0.1M Na2CO3 solution is added to the lithium-rich solution, the pH is adjusted to 8.8, stirred for 30 minutes, and the MgCO3 precipitate is removed by filtration. All other conditions are the same.

[0040] Comparative Example 1 The only difference between this comparative example and Example 1 is that MgCl2 and nano-Mg(OH)2 seed crystals are not added to the cathode chamber electrolyte in S2 (i.e., no Mg is added). 2+ (Source and seed crystals), all other conditions are the same.

[0041] Comparative Example 2 The only difference between this comparative example and Example 1 is that the deep magnesium removal step is missing in S4, while all other conditions are the same.

[0042] Comparative Example 3 The only difference between this comparative example and Example 1 is that the lithium removal solution in S4 was changed to 0.2M HCl (pH about 0.7), and all other conditions were the same.

[0043] Performance testing: 1. Determination of lithium enrichment factor and chloride ion blocking rate: The lithium enrichment factor was determined using the methods of Examples 1-4 and Comparative Examples 1-3. The test methods adopted were GB / T30902-2014 "Determination of Impurity Elements in Inorganic Chemical Products by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-OES)" and GB / T 5750.6-2023 "Standard Examination Methods for Drinking Water - Part 6: Metals and Metalloids".

[0044] The calculation formula is: Lithium enrichment factor = (n Li / n Mg ) LDH / (n Li / n Mg ) 海水 ; Where the initial n of the seawater Li / n Mg for: 0.17ppm / 1280ppm÷(6.94 / 24.3)≈1.4×10 -7 ; The chloride ion blocking rate of Examples 1-4 and Comparative Examples 1-3 was determined by means of: collecting electrolyte at the outlet of the anode chamber and determining the chloride ion blocking rate using ion chromatography (IC). - concentration; Cl - Barrier efficiency = (1-C) 海水中Cl- / C 阳极中Cl- )×100%; The test results are shown in Table 1 and Figure 1 As shown.

[0045] Table 1. Lithium enrichment factor and Cl - Barrier rate test results

[0046] As shown in Table 1, the lithium enrichment factor of Examples 1-4 is as high as 2780-3120 times, while that of Comparative Example 1 is only 12 times. The fundamental reason is that the OH produced by the cathode hydrogen evolution reaction in the examples... - A gradient alkaline microregion was formed (surface pH ≥ 12, bulk pH ≈ 10.5), under which Mg... 2+ and Li + A dense Li-Mg-LDH protective layer can be formed in situ on the electrode surface, which efficiently captures Li through an interlayer intercalation mechanism. + Meanwhile, the positively charged LDH layer affects Cl. - This generates electrostatic repulsion and physical barrier, thereby simultaneously achieving high lithium extraction selectivity and high Cl- content. - Barrier rate.

[0047] Comparative Example 1 without added Mg 2+ Without seed crystals, an LDH layer cannot be formed; only Mg crystals form on the cathode surface. 2+ The homogeneous precipitation forms a loose Mg(OH)₂, which cannot stably capture Li. + (Lithium enrichment is only 12 times) and for Cl - There was no effective barrier (barrier rate was only 32%); although LDH could be generated in the first cycle of Comparative Example 3, strong acid delithiation led to Mg... 2+ Significant leaching (28%) irreversibly disrupted the LDH layer structure, preventing the restoration of a complete LDH structure during secondary cycling. The lithium enrichment factor plummeted to 420, and Cl... - The barrier rate also dropped to 98.5%, which fully demonstrates that the weakly acidic buffer solution is crucial for maintaining the regeneration performance of LDH.

[0048] 2. Hydrogen production performance test: The test shall be conducted in accordance with GB / T 3634.1-2025 "Hydrogen Part 1: Industrial Hydrogen"; GB / T 3634.2-2025 "Hydrogen Part 2: Pure Hydrogen, High-Purity Hydrogen and Ultra-Purity Hydrogen"; and GB / T 19774-2005 "Technical Requirements for Water Electrolysis Hydrogen Production Systems". The formula for calculating the hydrogen production rate is: Hydrogen production rate = V 标准 / (electrode area × collection time); The formula for calculating Faraday efficiency is: Faraday efficiency (%) = (actual moles of hydrogen produced / theoretical moles of hydrogen produced) × 100%; The lithium hydride yield was determined according to GB / T 6283-2008 "Determination of Moisture Content in Chemical Products - Karl Fischer Method (General Method)". Lithium hydride yield (%) = Actual LiH production (moles) / Initial Li in lithium-rich solution + Number of moles × 100%; The test results are shown in Table 2 and Figure 2 As shown.

[0049] Table 2. Test results of hydrogen production rate, Faraday efficiency, and lithium hydride yield.

[0050] As shown in Table 2, the hydrogen production rates of Examples 1-4 were 485-560 mL / (cm²). 2 The efficiency (·h) and Faraday efficiency (91.2%-95%) are close to those of pure water electrolysis. This is because the in-situ generated LDH protective layer effectively blocks Cl-. - Reaching the anode (anode chamber Cl) - <5ppm), avoiding interference from the chlorine evolution side reaction on hydrogen production efficiency, while the good conductivity and porous structure of the LDH layer do not affect H + / Electronic transmission.

[0051] Comparative Example 1 lacks an LDH layer, Cl - Rapid penetration to the anode, chlorine evolution reaction (2Cl) - →Cl2+2e - Competition with the oxygen evolution reaction caused the Faraday efficiency to drop to 65% within 2 hours, and the hydrogen production rate also decreased accordingly; in the first cycle of Comparative Example 3, because the LDH structure was still intact, the hydrogen production performance was close to that of the Example, but in the second cycle, the LDH plate was destroyed by strong acid, and Cl - The reduced barrier properties led to a decrease in the hydrogen production rate to 280 and the Faraday efficiency to 78%. Regarding lithium hydride yield, Examples 1-4 all achieved 84%-87%, while Comparative Example 2, although achieving 86%, suffered from insufficient magnesium removal, resulting in high Mg content in the lithium-rich solution. 2+ During electrochemical hydrogenation, Li + The co-deposition of MgH2 impurities resulted in a LiH purity of only 82.3% (although the yield figure was high, the product was substandard), which shows that yield alone cannot be used to evaluate product quality.

[0052] 3. Electrode life test method: The test was conducted in accordance with GB / T 19774-2005 "Technical Requirements for Water Electrolysis Hydrogen Production System". By testing the electrode life, the actual protective effect of the LDH protective layer on the electrode can be quantitatively verified, proving whether it can effectively block chloride ions, inhibit chlorine evolution reaction and maintain electrode activity during long-term operation. The test results are shown in Table 3.

[0053] Table 3 Electrode life test results

[0054] As shown in Table 3, the electrode lifetimes of Examples 1-4 all exceeded 2000 hours, while Comparative Example 1 only lasted 4 hours and Comparative Example 3 only lasted 120 hours. The core difference lies in the integrity and stability of the LDH protective layer. In the examples, the LDH layer was in a dynamic growth / dissolution equilibrium state during electrolysis, which could continuously repair minor defects or corrosion points. At the same time, its dense nanosheet structure (approximately 500 nm thick) formed a stable physical barrier, allowing Cl... - Unable to contact the electrode substrate, thus greatly extending electrode life; Comparative Example 1 has no LDH layer at all, Cl - Direct attack on the electrode surface (especially the pore walls and grain boundaries of the nickel foam) caused rapid pitting corrosion, leading to failure within 4 hours; the LDH layer in Comparative Example 3 was severely corroded by strong acid in the first cycle, and the Mg in the layer... 2+ Significant loss and lattice collapse meant the regenerated LDH layer could not regain its density and adhesion, leading to peeling and cracking during the second electrolysis process. - It penetrates along the defect, thus the electrode lifetime is only 120 hours. This result also verifies the correlation between electrode lifetime and Cl. - Positive correlation between blocking rates: When the blocking rate is ≥99%, the lifetime is >2000 hours; when the blocking rate drops to 98.5%, the lifetime drops sharply to 120 hours.

[0055] 4. Delithiation performance and deep magnesium removal performance test: The method for determining the selectivity of delithiation is based on GB / T 30902-2014, "Determination of Impurity Elements in Inorganic Chemical Products by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)". The method for determining the deep magnesium removal effect was based on GB / T 30903-2014 "Determination of Impurity Elements in Inorganic Chemical Products - Inductively Coupled Plasma Mass Spectrometry (ICP-MS)" and GB / T 30902-2014 "Determination of Impurity Elements in Inorganic Chemical Products - Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)". The test results are shown in Table 4 and... Figure 3 As shown.

[0056] Table 4 Li + Desorption rate, Mg 2+ Dissolution rate test results

[0057] As shown in Table 4, all examples 1-4 used a weakly acidic buffer solution (pH 5.0-6.5) for lithium removal. +The desorption rate is as high as 91%-92.5%, while Mg 2+ The dissolution rate is only 4.1%-4.5%, because under weakly acidic conditions, H... + Capable of selectively exchanging Li between LDH layers + (Li) + (The bonding energy with the laminations is low), while the Mg in the laminations... 2+ Due to OH - It forms strong coordination bonds and is located in the crystal lattice framework, resulting in an extremely low dissolution rate at pH ≥ 5.0.

[0058] In Comparative Example 3, when 0.2M HCl (pH≈0.7) was used, high concentrations of H+... + Not only the interlayer Li + It will also attack the Mg-O bonds in the laminations, causing Mg to... 2+ Significant dissolution (28%) occurred, along with irreversible acid dissolution and rearrangement of the lamellar structure. This explains why Li in Comparative Example 3... + Although the desorption rate was slightly higher (94.2%), the regeneration performance of LDH was severely reduced.

[0059] Furthermore, Comparative Example 2 and Example 1 showed the same delithiation selectivity, but Comparative Example 2 lacked a deep magnesium removal step, resulting in residual Mg in the lithium-rich solution. 2+ (Mg / Li=0.04) MgH2 impurities will be formed during the subsequent hydrogenation process, which further illustrates the causal relationship between the delithiation selectivity index in Table 4 and the lithium hydride purity index in Table 2: even if the delithiation selectivity is good, the product purity will still not meet the standard if deep magnesium removal is not carried out.

[0060] Therefore, this invention employs the aforementioned method for producing hydrogen and extracting lithium from seawater and its application. Through deep synergy between hydrogen production and lithium extraction, a lithium-magnesium layered double hydroxide protective layer is generated in the gradient alkaline micro-region formed in situ during the cathode hydrogen evolution reaction. This protective layer simultaneously achieves multiple functions, including highly selective lithium extraction, efficient physical barrier against chloride ions, and resistance to electrode corrosion. Furthermore, the lithium extraction product is directly electrochemically hydrogenated to prepare high-value-added lithium hydride. Meanwhile, the byproducts dilute hydrochloric acid, regenerated adsorbent materials, and unreacted hydrogen are all recycled in a closed loop. This significantly improves the stability of seawater hydrogen production and the efficiency of lithium resource recovery while reducing chemical and energy consumption, thus realizing the integrated, clean, and high-value utilization of seawater resources.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for producing hydrogen and extracting lithium from seawater, characterized in that: Includes the following steps: S1. Construct a three-chamber electrolytic cell, in which the cathode chamber and the intermediate chamber are separated by a cation exchange membrane, and the intermediate chamber and the anode chamber are separated by a dense cation exchange membrane or an anion blocking membrane. S2, Injecting Mg-containing... 2+ An alkaline electrolyte containing nano-Mg(OH)2 seed crystals is introduced into the intermediate chamber, pretreated seawater is introduced into the anode chamber, and an inert electrolyte is injected into the anode chamber for electrolysis. S3, utilizing the OH generated by the cathode hydrogen evolution reaction - The formation of gradient alkaline microregions allows Mg migrating from seawater to... 2+ and Li + A lithium-magnesium layered double hydroxide protective layer was generated in situ on the cathode surface, while Li was extracted. + And block Cl - ; S4. Treat the lithium-magnesium layered double hydroxide protective layer obtained in S3 with a weakly acidic buffer solution to selectively remove Li. + The lithium-rich solution and regenerated LDH are obtained, and the lithium-rich solution is subjected to deep magnesium removal to obtain a magnesium-removed lithium-rich solution. S5. Under anhydrous and oxygen-free conditions, the magnesium-free lithium-rich solution obtained in S4 is subjected to an electrochemical hydrogenation reaction by introducing hydrogen gas with a gas diffusion electrode as the cathode to generate lithium hydride. The unreacted hydrogen gas is recycled to the hydrogen inlet, and the lithium hydride is separated, washed, and dried under anhydrous and oxygen-free conditions.

2. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S2, seawater pretreatment includes microfiltration and pH adjustment to 7.5-8.0 with dilute hydrochloric acid, which is a byproduct generated at the diaphragm between the anode chamber and the intermediate chamber in S1.

3. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S3, the gradient alkaline microregion controls the initial pH of the cathode chamber to be 10-11 and the current density to be 50-150 mA / cm². 2 This achieves a local pH ≥ 12 on the electrode surface, while the pH ≤ 10.5 is achieved at locations far from the electrode.

4. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S3, the thickness of the lithium-magnesium layered double hydroxide protective layer is 100nm-2μm, and the specific surface area is >50m². 2 / g, for Cl - The barrier efficiency is ≥99%.

5. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S4, the weakly acidic buffer is one of citrate-sodium citrate buffer, acetic acid-ammonium acetate buffer, or formic acid-sodium formate buffer, with a pH range of 5.0-6.

5.

6. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S4, deep magnesium removal is achieved using chelating resin adsorption or carbonate / phosphate precipitation.

7. The method for producing hydrogen and extracting lithium from seawater according to claim 1, characterized in that: In S5, the conditions for the electrochemical hydrogenation reaction are: current density 5-20 mA / cm². 2 Hydrogen pressure 0.1-0.5MPa, temperature 20-40℃, electrolyte water content <1000ppm.

8. An application of seawater hydrogen production and lithium extraction, wherein the method for seawater hydrogen production and lithium extraction according to any one of claims 1-7 is applied to the preparation of hydrogen storage materials, solid electrolytes, or organic synthesis reducing agents.

Images