Solid polymer polyelectrolyte for water electrolysis

Abstract

The application relates to a high-efficiency electrode material for solid polymer water electrolysis, in particular to a low-oxygen-evolution-potential electrode taking a base metal as a raw material and a preparation method thereof. The method obtains a heteropolyacid compound with a vacancy-type Dawson structure through co-precipitation and nanoscale grading technology, and the molecular formula of the heteropolyacid compound is Na8K 18 [Sc 12 (H2O)6(OH)3(HPO4)2(Se2Mo 18 O 62 )3]xH2O. The catalyst has an oxygen evolution reaction overpotential lower than 300 mV, and a cycle life of up to 200 h at 1 Acm – 2 When compared with a traditional noble metal electrode, the base metal electrode of the application not only has a lower cost, but also exhibits excellent electrocatalytic activity and stability, can maintain high-efficiency performance under long-time operation, and provides an economic and efficient solution for the wide application of solid polymer water electrolysis technology.

Description

I. Technical Field

[0001] This invention relates to the field of electrochemical new energy technology, specifically to a base metal low oxygen evolution potential electrode for solid polymer water electrolysis and its preparation method. II. Background Technology

[0002] Solid polymer electrolyte water electrolysis (SPEWE) technology has received widespread attention and developed rapidly since the 1970s. Originally proposed by General Electric in the United States and applied to the fuel cell system of the Gemini spacecraft, SPEWE pioneered the field of solid polymer electrolytes (SPE). Since then, SPE technology has been widely used in hydrogen-oxygen fuel cells, water electrolysis, and organic electrochemical synthesis due to its advantages such as high efficiency, safety, simple structure, and stable performance. Compared with traditional alkaline water electrolysis, SPE water electrolysis technology has advantages such as high efficiency (close to 100%), high current density, high safety (using pure water as the electrolyte, avoiding corrosion), simple structure (no cooling system required), and long lifespan (the longest chamber life exceeds 30 years). However, SPE technology also faces some challenges, such as the low ionic conductivity, low thermal stability, and contact resistance of polymer solid electrolytes, which limit its widespread application in practice.

[0003] In solid polymer electrolysis (SPE) water electrolysis technology, commonly used anode materials mainly include noble metals such as rhodium (Ru) and iridium (Ir). These materials exhibit good catalytic activity and stability in strongly acidic environments. For example, the combination of Nation membranes and noble metal catalysts is the core of SPE electrolysis technology, with Nation membranes widely used due to their excellent chemical stability, mechanical stability, and high ion conductivity. However, the high cost of noble metals limits the widespread application of SPE electrolysis technology. It is estimated that theoretically 700 kg of iridium or rhodium is needed to obtain 1 gigawatt of electricity, but iridium and rhodium are expensive and in short supply. Therefore, developing low-cost, high-performance anode materials has become a current research hotspot. Currently, research mainly focuses on reducing the amount of noble metals used and developing base metal electrodes through alloying and other methods to improve catalytic performance and reduce costs.

[0004] Base metal low oxygen evolution potential (OEP) electrodes offer a significant cost advantage over current noble metal anode materials. The cost of base metals is approximately 1 / 1000th that of iridium, making them promising candidates for in-situ hydrogen production electrodes combining solar and wind power generation with PEM water electrolysis. Furthermore, base metal electrodes exhibit good catalytic activity even in corrosive environments, potentially replacing noble metal electrodes. For example, patent CN109478653A developed an oxygen evolution potential (OER) electrode whose metal layer comprises compounds formed from nickel, cobalt, manganese, and combinations thereof, exhibiting low OEP; patent CN115710727A relates to a hollow-framework high-entropy oxide oxygen evolution catalyst and its preparation method; and invention CN113802137A developed an OER electrode with metal nanoclusters and a metal support, wherein the metal nanoclusters include a core and organic thiol ligands, exhibiting low OEP and high stability. However, base metal electrodes also face some challenges, such as easy passivation and relatively low catalytic activity. To address these issues, researchers have developed base metal electrodes that exhibit their original catalytic activity even in corrosive environments by alloying easily passivated base metals with highly catalytically active base metals. Furthermore, optimizing the catalytic layer structure, improving electrode fabrication methods, and enhancing the corrosion resistance of the diffusion layer are also crucial for improving the performance of water electrolyzers. III. Summary of the Invention

[0005] This invention addresses the problems existing in the prior art. For catalyst activity and stability issues, their composition and structure can be optimized, such as through doping and alloying, and the construction of core-shell structures; suitable supports can be selected, including metal oxides and carbon materials; and novel catalysts, such as non-precious metals and single-atom catalysts, can be developed. To address high costs, the amount of precious metals used can be reduced, the preparation process optimized to improve dispersion, and cost-effective alternative materials and composite materials developed. To solve electrolyte compatibility issues, surface modification can be performed, such as treating the anode material surface or adding additives to the electrolyte. Simultaneously, the electrode structure can be optimized, with the design of three-dimensional electrodes and the fabrication of integrated electrodes. For electrode structure optimization, template methods and freeze-drying methods are used to control the pore structure, construct intermediate layers, and optimize the preparation process for interface engineering to improve electrode performance and electrolyte compatibility.

[0006] Heteropolyacids are excellent ion-conducting materials. Because their structure was proposed by J.F. Keggin in 1933, it is generally called the Keggin structure. It possesses complete tetrahedral symmetry, with twelve coordinating atoms connected to an oxygen atom forming a cage, and the nucleus at the center. In recent research, we discovered a novel Dawson structure with the general formula [Se₂Mo₃]. 18 O 62 ] n- The central Se atom is centered in a SeO4 tetrahedron, surrounded by four Mo3O atoms connected at the same angle.12 Trimetallic clusters are connected at the same angle to the central tetrahedron. Each trimetallic cluster consists of three MoO6 octahedra sharing a common edge, which can be viewed as two Keggin structure ions each having one Mo3O ion removed. 12 The trimetallic cluster ultimately forms a 1:17 series of vacancy-type Dawson structures, which have been shown to possess excellent charge conductivity and chemical stability. In addition to the core heteropolyacid unit, transition metal elements, alkali metal elements, and phosphate coordination structures are introduced as stabilizers, resulting in a Dawson structure material with the molecular formula Na8K. 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 [3]·xH2O. The material represented by this molecular formula is the core active component of the base metal low oxygen evolution potential electrode used in solid polymer water electrolysis.

[0007] To achieve the above objectives, the present invention provides a base metal low oxygen evolution potential electrode for solid polymer water electrolysis and its preparation method, characterized in that the preparation method of the electrode includes the following steps:

[0008] Step 1: Grind SeCl4 and (NH4)2MoO4 in a mortar and pestle at a molar ratio of 1:9, add them to ultrapure water, and stir vigorously to form a pale yellow aqueous solution with a mixed mass concentration of 10%.

[0009] Step 2: Adjust the pH of the pale yellow aqueous solution obtained in Step 1 to 4 with phosphoric acid, add excess ScCl3 until completely dissolved, at which point the molar ratio of Sc to Se should be greater than 2, to obtain solution A;

[0010] Step 3: Prepare a mixed solution of NaOH and KOH with a molar ratio of 4:9 and a mixed mass concentration of 25% to obtain mixed alkaline solution B;

[0011] Step 4: Add the mixed alkaline solution B obtained in step 3 dropwise to solution A and monitor the change in pH value. When the pH value reaches 6, the solution gradually becomes turbid. At this time, stop adding the solution and stir vigorously. A large number of flocs will quickly form in solution A, but they will break up again as the stirring continues.

[0012] Step 5: After stirring continuously for 30 minutes, stop stirring and dialyze overnight using a 10,000 Da dialysis bag. Centrifuge the obtained dialysate at 15,000 rpm and then separate it by nanofiltration. Wash the obtained pale yellow nanoparticles repeatedly with ultrapure water and acetone, and then let them air dry overnight.

[0013] Step 6: Place the solid particles obtained in step 5 into a quartz boat and calcine them in a vacuum oven at 350°C for 1 hour. The resulting black sample is then immersed in an imidazole solution.

[0014] Step 7: Pour the solid particles soaked in imidazole obtained in step 6 into a ball mill and continue milling for 3 hours. Then, dialyze overnight using a 10,000 Da dialysis bag. After centrifuging the obtained dialysate at 15,000 rpm, separate it by nanofiltration to obtain nanoparticles.

[0015] Step 8: Disperse the nanoparticles obtained in Step 7 in a Nafion solution with a mass concentration of 5%, at which point the mass concentration of the nanoparticles is 20%. Disperse the nanoparticles for 5 minutes under 1kW ultra-high frequency ultrasound to form a uniformly dispersed nanoparticle solution.

[0016] Step 9: The nanoparticle solution obtained in Step 8 is uniformly coated onto the surface of hydrophilic carbon paper and dried at 150°C for 15 minutes to obtain a carbon paper catalyst material with an oxygen evolution catalytic active coating.

[0017] For the above technical solution, it is further specified that the purity of NaOH and KOH mentioned in step 3 should be higher than 95%, and the solution should be sealed immediately after preparation to prevent the absorption of CO2 in the air and the generation of bicarbonate, which would affect the purity of the product.

[0018] For the above technical solution, the molecular formula of the particulate matter obtained in step 5 is further specified as Na8K. 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 [3]·xH2O is a heteropolyacid compound with a missing Dawson structure.

[0019] For the above technical solution, the hydrophilic carbon paper selected in step 9 can be the TGP-H-60 series from Toray Industries, Inc. of Japan, the SGL-30 series from the United States, or the HCP010N series carbon paper from Sanshe Company of Shanghai, China.

[0020] The advantages of this invention are:

[0021] 1) The structure is highly symmetrical and stable, and can maintain a good morphology during electrocatalysis, providing a stable framework for catalytic reactions.

[0022] 2) Synergistic effects can occur between Sc-Mo-Se elements, enhancing catalytic activity. For example, transition metals can adjust the electronic structure, promoting the oxygen evolution reaction. They possess abundant redox active sites, effectively adsorbing reaction intermediates and lowering the reaction energy barrier.

[0023] 3) Simultaneously, the Dawson structure typically exhibits good electrical conductivity, which can accelerate electron transport and improve electrocatalytic efficiency. Furthermore, this structure possesses a certain degree of corrosion resistance, maintaining stability for a considerable period under harsh electrocatalytic conditions.

[0024] 4) Compared with other anode materials, the Dawson structure is relatively easy to synthesize and can be controlled by a variety of methods to meet different application requirements. IV. Description of the attached drawings

[0025] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the following description of the specific embodiments are briefly explained. Figure 1 Na8K with Dawson structure 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 Transmission electron microscope image of xH2O material;

[0026] Figure 2 For electrocatalysis, the Dawson structure Na8K was used sequentially. 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 X-ray diffraction image of xH2O material.

[0027] Figure 3 Na8K with Dawson structure 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 Comparison of linear scanning voltammetric curves of xH2O material with those of carbon paper and RuO2. V. Detailed Implementation Methods

[0028] The present invention will now be described in detail with reference to the accompanying drawings and embodiments:

[0029] Example 1:

[0030] A base metal low oxygen evolution potential electrode for solid polymer water electrolysis and its preparation method are disclosed. The preparation method includes the following steps: First, SeCl4 and (NH4)2MoO4 with a molar ratio of 1:9 are thoroughly ground in a mortar and pestle, then added to ultrapure water and stirred vigorously to form a pale yellow aqueous solution with a mixed mass concentration of 10%. The pH of the obtained pale yellow aqueous solution is adjusted to 4 with phosphoric acid, and excess ScCl3 is added until completely dissolved. At this point, the molar ratio of Sc to Se should be greater than 2, resulting in solution A. A mixed solution of NaOH and KOH with a molar ratio of 4:9 and a mixed mass concentration of 25% is prepared. At this point, the purity of both NaOH and KOH should be higher than 95%. The solution is immediately sealed after preparation. To prevent the absorption of CO2 from the air and avoid the impact of bicarbonate on product purity, a mixed alkaline solution B was obtained after mixing. This solution B was added dropwise to solution A, and the pH was monitored. When the pH reached 6, the solution gradually became turbid. At this point, the addition was stopped and the mixture was stirred vigorously. A large number of flocs rapidly formed in solution A, but these flocs broke up again with further stirring. After stirring for 30 minutes, the stirring was stopped, and the solution was dialyzed overnight using a 10,000 Da dialysis bag. The resulting dialysate was centrifuged at 15,000 rpm and then separated by nanofiltration. The resulting pale yellow nanoparticles were repeatedly washed with ultrapure water and acetone, and then air-dried overnight. A transmission electron microscope image of the material is attached. Figure 1 The X-ray diffraction pattern is shown in the attached figure. Figure 2 As shown, the molecular formula of the particles obtained at this time is Na8K. 18 [Sc 12 (H₂O)₆(OH)₃(HPO₄)₂(Se₂Mo) 18 O 62 [3]·xH2O is a heteropolyacid compound with a missing Dawson structure; the above solid particles were placed in a quartz boat and calcined at 350°C in a vacuum oven for 1 hour, and the resulting black sample was soaked in an imidazole solution; the solid particles soaked in imidazole were poured into a ball mill and milled continuously for 3 hours, and then dialyzed overnight using a 10,000 Da dialysis bag. The dialysate was centrifuged at 15,000 rpm and then separated by nanofiltration to obtain nanoparticles; the nanoparticles were dispersed in a 5% N2 solution. In the afion solution, the mass concentration of nanoparticles is 20%. The nanoparticles are dispersed under 1kW ultra-high frequency ultrasound for 5 minutes to form a uniformly dispersed nanoparticle solution. The nanoparticle solution is then uniformly coated onto the surface of hydrophilic carbon paper. The hydrophilic carbon paper can be one of the following: TGP-H-60 series from Toray Industries, Japan; SGL-30 series from the United States; or HCP010N series from Sanshen Chemical Co., Ltd. in Shanghai, China. The carbon paper is dried at 150°C for 15 minutes to obtain a carbon paper catalyst material with an oxygen evolution catalytic activity coating.

[0031] Example 2:

[0032] Electrochemical tests were conducted on the carbon paper catalyst material with an oxygen evolution catalytic active coating obtained by the preparation method described in Example 1.

[0033] A three-electrode system was constructed using a CHI-660D electrochemical workstation manufactured by Shanghai Chenhua Co., Ltd. to evaluate the electrocatalytic oxygen evolution (OER) activity of the prepared carbon paper catalyst material with an oxygen evolution catalytic active coating. Specifically, the carbon paper catalyst was used as the working electrode (WE), the platinum sheet as the counter electrode (CE), and the Hg / HgO electrode as the reference electrode (RE). The electrochemical reaction was carried out at 1.0 mol / L... -1 Linear sweep voltammetry (LSV) tests were performed in an alkaline environment with KOH. During the test, the voltammetry was conducted at a rate of 5 mV / s. -1 The scan rate is linearly scanned within the range of +1.4 to +2.0 V relative to the reversible hydrogen electrode (RHE). The conversion of the electrode potential relative to the standard hydrogen electrode is based on formula E. RHE =0.098V + pH × 0.059V for correction.

[0034] The carbon paper catalyst material with the oxygen evolution catalytic active coating obtained above was subjected to linear scanning voltammetry using an electrochemical workstation. The results are shown in the attached figure. Figure 3 As shown, its oxygen evolution potential (OEP is approximately 1.49V vs. RHE) is superior to that of carbon paper and RuO2 electrodes.

[0035] Example 3:

[0036] Electrochemical tests were conducted on the carbon paper catalyst material with an oxygen evolution catalytic active coating obtained by the preparation method described in Example 1.

[0037] The electrochemical workstation and electrode configuration were as in Example 2, and cyclic voltammetry (CV) was used. Tests were conducted at 1.0 mol / L... -1 The scan was performed in KOH electrolyte, using the non-Radar region of the selected electrode (0.1-0.2V vs. RHE) as the scan range, with a scan frequency of 10 to 60 mV s. -1 CV scans were performed at different scan rates. Subsequently, the equivalent electrochemical active area (ECSA) value was calculated by plotting and fitting the CV curves of the same sample at different scan rates. The magnitude of the ECSA value directly reflects the number of active sites on the electrode surface.

[0038] Calculations show that the ECSA of the carbon paper catalyst material with oxygen evolution catalytic active coating prepared in Example 1 is 156 cm⁻¹. 2 This is much larger than the 12.5 cm of carbon paper and RuO2 electrodes. 2 and 96cm 2 It has more surface active sites.

[0039] Example 4:

[0040] Electrochemical tests were conducted on the carbon paper catalyst material with an oxygen evolution catalytic active coating obtained by the preparation method described in Example 1.

[0041] The electrochemical workstation and electrode configuration were as described in Example 2. Electrochemical impedance spectroscopy (EIS) was performed on the electrode samples to analyze the charge transport characteristics at the electrode interface. The tests were conducted at a bias voltage of 250 mV relative to RHE, covering a frequency range from 100 mHz to 100 kHz, with a fixed amplitude of 10 mV.

[0042] Calculations show that the Tafel slope of the carbon paper catalyst material with an oxygen evolution catalytic active coating prepared in Example 1 is 115.27 mV dec. -1 The Tafel slope of the carbon paper and RuO2 electrodes is 165.42 mV dec. -1 and 105.16mV dec -1 Similarly, this indicates that the catalyst active layer did not affect charge transport.

[0043] Example 5:

[0044] Electrochemical tests were conducted on the carbon paper catalyst material with an oxygen evolution catalytic active coating obtained by the preparation method described in Example 1.

[0045] The electrochemical workstation and electrode configuration were as described in Example 2, and two methods were employed: accelerated durability testing (ADT) and chronopotential curve testing. The ADT test was conducted within a linear scan range of 0.1–0.3 V vs. RHE, at a frequency of 0.1 V s. -1 After performing 10,000 cyclic CV scans on the electrode at a certain scan rate, an LSV test was performed again, focusing on the electrode reaching 10 mA cm⁻¹. -2 Overpotential change at current density.

[0046] Chronopotential curve testing was performed at room temperature with a constant 10 mA cm⁻¹. -2 The current density was measured, and the stability changes of the overpotential were continuously monitored and recorded. The test duration was set to 240 hours.

[0047] The results showed that the carbon paper catalyst material with oxygen evolution catalytic activity coating prepared in Example 1 had good electrochemical activity and stability. After a test period of 240 h, although the overpotential fluctuated greatly due to the swelling caused by prolonged alkali soaking, the change in average electrode overpotential was only 55 mV. In contrast, the carbon paper did not show significant changes. However, the RuO2 electrode showed a significant increase in overpotential after 117 h, and after 240 h of testing, its activity was completely lost, and it no longer had OER catalytic activity.

[0048] The specific embodiments described above are only used to illustrate the spirit of the present invention. The scope of protection of the present invention is not limited thereto. For those skilled in the art, other embodiments can be easily made by means of changes, substitutions or modifications based on the technical content disclosed in this specification. All such other embodiments should be covered within the scope of protection of the present invention.

Claims

1. A solid polymer polyelectrolyte for water electrolysis of a base metal low-oxygen evolution potential electrode, characterized by, The preparation method of the electrode comprises the following steps: Step 1, SeCl4 and (NH4)2MoO4 with a molar ratio of 1:9 are fully ground with a mortar, then added into ultrapure water, and stirred intensively to prepare a light yellow aqueous solution with a mixed mass concentration of 10%; Step 2, the light yellow aqueous solution obtained in step 1 is adjusted to a pH value of 4 with phosphoric acid, and an excess of ScCl3 is added until completely dissolved, at this time, the molar ratio of Sc to Se should be greater than 2, to obtain solution A; Step 3, a mixed solution of NaOH and KOH with a molar ratio of 4:9 is prepared, and the mixed mass concentration is 25%, to obtain mixed alkali solution B; Step 4, the mixed alkali solution B obtained in step 3 is added dropwise into solution A, and the change of pH value is monitored, when the pH value reaches 6, the solution gradually becomes turbid, at this time, the dropwise adding is stopped and the solution is stirred intensively, a large amount of flocculation is rapidly formed in solution A, but it is broken again with stirring; Step 5, after continuous stirring for 30 minutes, the stirring is stopped, and the solution is transferred to a dialysis bag with a molecular weight of 10,000 Da for dialysis overnight, the obtained dialysate is centrifuged at a high speed of 1,5000, then separated by nanofiltration, the obtained light yellow nanoparticles are repeatedly washed with ultrapure water and acetone, and then dried in air overnight; Step 6, the solid particles obtained in step 5 are placed in a quartz boat and calcined in a vacuum oven at 350℃ for 1 hour, and the obtained black sample is immersed in an imidazole solution; Step 7, the solid particles immersed in imidazole obtained in step 6 are poured into a ball mill and continuously ground for 3 hours, and then dialyzed again in a dialysis bag with a molecular weight of 10,000 Da overnight, the obtained dialysate is centrifuged at a high speed of 1,5000, then separated by nanofiltration, to obtain nanoparticles; Step 8, the nanoparticles obtained in step 7 are dispersed in a Nafion solution with a mass concentration of 5%, at this time, the mass concentration of the nanoparticles is 20%, and the nanoparticles are dispersed under ultrasonic waves with a power of 1 kW for 5 minutes to form a uniformly dispersed nanoparticle solution; Step 9, the nanoparticle solution obtained in step 8 is uniformly coated on the surface of a hydrophilic carbon paper, and dried at 150℃ for 15 minutes to obtain a carbon paper catalyst material with an oxygen evolution catalytic coating.

2. The solid polymerized low-oxygen-evolution-potential electrode of a base metal for water electrolysis according to claim 1, wherein The purity of NaOH and KOH in step 3 should be higher than 95%, and the prepared solution should be sealed immediately to prevent the absorption of CO2 in the air and the generation of bicarbonate which affects the purity of the product.

3. The solid polymerized low-oxygen-evolution-potential electrode of a base metal for water electrolysis according to claim 1, wherein The molecular formula of the particles obtained in Step 5 is Na8K 18 [Sc 12 (H2O)6(OH)3(HPO4)2(Se2Mo 18 O 62 )3]·xH2O is a heteropolyacid compound of a vacant Dawson structure.

4. The solid polymerized low-oxygen-evolution-potential electrode of a base metal for water electrolysis according to claim 1, wherein The hydrophilic carbon paper selected in step 9 is TGP-H-60 series, SGL-30 series or HCP010N series carbon paper.

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