A method for preparing an electrocatalyst for electrolysis of seawater at amperometric current with ultra-stability
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2023-05-09
- Publication Date
- 2026-06-09
AI Technical Summary
Existing LDHs-based OER electrocatalysts exhibit poor stability during alkaline seawater electrolysis, cannot operate stably for extended periods under high current, and are also costly.
By adjusting the Co/Fe atomic molar ratio to 0.7–1.4 and introducing CO32- ions as an intermediate layer, CoFe-Ci@GQDs were prepared using graphene quantum dot surface modification. These were then loaded onto nickel foam to form CoFe-LDH nanosheets, enhancing their stability and conductivity in alkaline seawater.
It achieves long-term stability of seawater electrolysis under ampere-level current, with a current density of up to 1.2A, and can run continuously for more than 100 hours, significantly improving the stability and conductivity of the catalyst.
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Figure CN116516402B_ABST
Abstract
Description
Technical Field
[0001] This invention discloses a method for preparing an ultra-stable electrocatalyst capable of electrolyzing seawater at ampere-level currents. This method improves the electrolysis performance of CoFe-LDH on water / seawater by adjusting the morphology of layered double metal hydroxide (LDH) nanosheets, the proportion of metal atoms in the host layer, interlayer anions, and surface-modified graphene quantum dots. The improved catalyst has a significantly enhanced current and can electrolyze water / seawater for extended periods at ampere-level high currents, belonging to the field of electrocatalysis. Background Technology
[0002] Electrolysis of water powered by renewable energy is a promising green approach to hydrogen production. For large-scale deployment of electrocatalytic hydrogen production, in addition to considering the cost of electrolyzers and the availability of renewable electricity, water supply is a practical issue. Generally, existing electrolysis technologies require ultrapure deionized water with a resistivity of 18.2 MΩcm or alkaline solutions containing impurities below ppm, meaning that the water source should undergo multi-stage desalination and thorough purification before entering the reactor. This water pretreatment not only complicates the configuration of the electrolyzer but also increases design and maintenance costs. Direct electrolysis of low-quality water, such as seawater, can bypass these electrolyzer design problems. Seawater accounts for 96.5% of the Earth's total water volume; if it could be directly supplied to electrolyzers, the growing hydrogen economy would not exacerbate freshwater shortages caused by population growth and water pollution.
[0003] Direct electrolysis of low-quality water, such as seawater, requires stricter standards for the membranes and electrocatalysts / electrodes used in its components, particularly the anode OER electrocatalyst / electrode. The main technological challenges in seawater electrolysis stem from Cl... - Caused by the presence of ions, Cl - The average concentration of Cl- ions in seawater is approximately 0.5 M. Theoretically, Cl- - Ion oxidation produces Cl2 or HOCl / OCl - Thermodynamically, it is always inferior to OER, and the maximum potential difference between it and OER in the alkaline region can reach about 490mV.
[0004] LDHs possess a unique layered structure, large specific surface area, tunable composition, and high OER activity in alkaline media, making them a promising class of OER electrocatalysts for alkaline seawater electrolysis. However, in practice, the stability exhibited by current LDHs is far from satisfactory. This indicates that previously developed LDH-based OER electrocatalysts have limitations in their ability to react with Cl-. - The ions exhibit poor corrosion resistance. The instability of these LDHs during alkaline seawater electrolysis may have three causes. The first reason might be that these LDHs have a higher corrosion resistance than water / OH- ions. - Ions exhibit higher Cl- Adsorption or coordination tendencies mean that, as the seawater electrolysis process progresses, these LDHs gradually lose their OER activity due to contamination or occupation of their active sites. A second reason might be Cl... - Intercalation can cause the collapse of the layered structure of LDHs or catalyst detachment. A third reason may be the continuous loss of metal ions from the host layer during catalysis, leading to catalyst structural collapse and eventual deactivation. Therefore, to enable these abundant and readily available LDHs to effectively and stably electrolyze alkaline seawater, in addition to optimizing the composition of their metal-containing host layer to improve OER activity, composition / structure regulation should be applied to their surface and interlayer layers to achieve Cl-like properties. - Repulsion ability or tolerance to Cl - It has strong corrosion resistance and greatly inhibits the loss of the main layer metal.
[0005] Wu et al. (Journal of Power Sources, 532(2022), 231353) prepared Pt-CoFe(II)LDHs by electrodepositing CoFe(II)LDHs electrocatalysts onto nickel foam (NF), followed by impregnation to reduce and anchor Pt clusters, using a spontaneous redox method. Pt-CoFe(II)LDHs only required OER overpotentials of 239, 302, and 375 mV to achieve 10, 100, and 500 mA cm⁻¹, respectively. -2 The current density can reach 100 mA / cm². -2 and 500mAcm -2 It maintains stability for 40 hours at a high current density. However, this method has the following technical problems: it requires the use of precious metals, resulting in high costs, and it cannot achieve long-term seawater decomposition under high current.
[0006] Therefore, there is a need for an electrocatalyst that is stable, low in cost, and can achieve long-term seawater decomposition under high current. Summary of the Invention
[0007] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing an ultra-stable electrocatalyst capable of electrolyzing seawater at ampere-level currents. The preparation method provided by this invention is low-cost, simple, and produces CoFe-C... i @GQDs exhibit excellent stability in seawater electrolysis and have high practical application value.
[0008] The inventive concept of this invention is as follows: This invention selects Co and Fe elements as building blocks for the two-dimensional main layer, with an atomic molar ratio close to one to one, and incorporates CO3... 2- Ions introduced into the intermediate layer, resulting in CoFe-C iIt acts as a highly efficient and stable OER electrocatalyst in alkaline simulated seawater; the surface modification of graphene quantum dots further enhances CoFe-C i @GQDs are able to drive continuous seawater electrolysis for over 2400 hours at ampere-level currents, making them the most durable OER electrocatalyst reported for seawater to date.
[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0010] To fully utilize the OER electrode, CoFe-C i Nanosheets were deposited on nickel foam substrates (1 mm to 5 mm thick) using a hydrothermal process. The molar ratio of Co / Fe metal atoms in the host layer was 0.7 to 1.4, and the total content of Co and Fe metal ions in the precursor solution was controlled at 3.5-4.5 mmol / L. The surfactant Na3C6H5O7·2H2O was added at a concentration of 0.4-0.6 mM, and urea was used as a precipitant to provide CO3. 2- Intercalated anions.
[0011] The present invention relates to a method for preparing an ultra-stable electrocatalyst capable of electrolyzing seawater at ampere-level currents.
[0012] The electrocatalyst comprises a conductive substrate, nickel foam (NF), CoFe-LDH (Co / Fe atomic molar ratio of approximately 0.7–1.4, with carbonate ions as intercalation anions) providing active sites, and GQDs supported on the LDH to enhance conductivity.
[0013] The method includes the following steps:
[0014] 1) Dissolve Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O and urea in deionized water and stir to form a transparent precursor solution; wherein, the molar ratio of Co / Fe metal atoms is 0.7-1.4; the total content of Co and Fe metal ions in the precursor solution is controlled at 3.5-4.5 mmol / L;
[0015] 2) Transfer the transparent solution from step 1) to a hydrothermal reactor, add clean and dry nickel foam, carry out the first thermal synthesis reaction, and then allow it to cool naturally to room temperature;
[0016] 3) Rinse the sample obtained in step 2) with distilled water and then dry it;
[0017] 4) Dilute the GQDs solution with deionized water, transfer it to a hydrothermal reactor, add the sample obtained in step 3), and carry out a second thermal synthesis reaction. After cooling to room temperature, wash and dry to obtain the electrocatalyst CoFe-C of the present invention. i @GQDs / NF.
[0018] Further, in step 1), the concentration of Co(NO3)2·6H2O in the precursor solution is 1.5-2.5 mmol / L. More preferably, the concentration is 2-2.5 mmol / L.
[0019] Further, in step 1), the concentration of Fe(NO3)3·9H2O in the precursor solution is 1.5-2.5 mmol / L. More preferably, the concentration is 1.5-2 mmol / L.
[0020] Further, in step 1), the concentration of Na3C6H5O7·2H2O in the precursor solution is 0.4-0.6 mmol / L. More preferably, the concentration is 0.5-0.6 mmol / L.
[0021] Further, in step 1), the urea concentration in the precursor solution is 4-6 mmol / L. More preferably, the urea concentration is 5 mmol / L.
[0022] Furthermore, in step 2), the first thermal synthesis reaction is carried out at 120°C for 10 hours.
[0023] Furthermore, in step 3), the drying method is to dry at 60°C under vacuum conditions.
[0024] Furthermore, in step 4), the GQDs solution is an existing product, which is a solution in which GQDs are dispersed in ethanol and a small amount of DMF, with a concentration of 1 mg / mL; the dilution method of GQDs graphene quantum dots is: each 1 mL of 1 mg / mL GQDs solution is diluted with deionized water to 20 mL.
[0025] Furthermore, in step 4), the reaction temperature of the second thermal synthesis reaction is 150°C, and the reaction time is 3 hours.
[0026] Compared with the prior art, the improvements of this invention and the resulting technical effects are as follows:
[0027] 1) This invention regulates the metal cation vacancy formation energy by adjusting the Co / Fe atomic molar ratio to 0.7-1.4, making it less likely for metal ions to be lost and the catalyst structure to collapse and deactivate.
[0028] 2) CO3 2- Ions introduced into the intermediate layer, resulting in CoFe-C i It acts as a highly efficient and robust OER electrocatalyst in alkaline simulated seawater; CoFe-C i Nanosheets generate almost no interlayer CO3 during seawater electrolysis. 2- Ions and Cl -The exchange of ions effectively inhibits the collapse or peeling of the layered structure;
[0029] 3) The negative charge property of graphene quantum dots will, to some extent, hinder the development of CoFe-C i Nanosheet surface active sites for Cl - Unfavorable adsorption or coordination, surface modification further enhances CoFe-C i @GQDs can drive continuous electrolysis of seawater at ampere-level currents.
[0030] 4) The amount of surfactant Na3C6H5O7·2H2O added is 0.4-0.6mM, which controls the edge of the nanosheet to be serrated, with more dangling bonds and active adsorption sites. Attached Figure Description
[0031] Figure 1 The CoFe-C prepared by the method of this invention i Scanning electron microscope (SEM) image. From Figure 1 It can be seen that the prepared LDH nanosheets have serrated edges and more edge adsorption sites.
[0032] Figure 2 The CoFe-C prepared by the method of this invention i Transmission electron microscopy (TEM) images from @GQDs. Figure 2 It can be seen that GQDs were successfully loaded onto CoFe-C. i surface.
[0033] Figure 3 The CoFe-C prepared by the method of this invention i @GQDs's performance chart for seawater electrolysis.
[0034] Figure 4 The CoFe-C prepared by the method of this invention i @GQDs's diagram of the stability performance of seawater electrolysis. Detailed Implementation
[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are only used to illustrate the present invention and help those skilled in the art to further understand it, and are not intended to limit the present invention in any way. Reasonable improvements and adjustments made by those skilled in the art based on the concept of the present invention shall fall within the protection scope of the present invention.
[0036] Ferric nitrate nonahydrate (Fe(NO3)3·9H2O), potassium hydroxide (KOH), and urea were purchased from Aladdin. Cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and sodium chloride were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All chemicals were used as is without further purification. Graphene oxide quantum dot (GQD) solution (1 mg / mL) -1 Purchased from Nanjing Xianfeng Nanotechnology Co., Ltd.
[0037] Example 1
[0038] Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O, and urea were dissolved in 60 mL of deionized water and stirred to form a transparent solution. The concentrations of Co(NO3)2·6H2O were 2.5 mM, Fe(NO3)3·9H2O were 2 mM, and the Co / Fe atomic molar ratio was 1.25; the concentrations of Na3C6H5O7·2H2O were 0.5 mM, and the urea concentration was 5 mM. The transparent solution was transferred to a 100 mL hydrothermal reactor, and a cleaned and dried 1 cm × 2 cm piece of nickel foam was added. The reactor was placed in an oven and kept at 120 °C for 10 h, then allowed to cool naturally to room temperature. The sample was rinsed with distilled water and then dried under vacuum at 60 °C. 1 mL of the LGQDs solution was diluted with deionized water to 20 mL, transferred to a 50 mL hydrothermal reactor, and the dried sample was added. The hydrothermal reactor was placed in an oven at 150°C for 3 hours. After cooling to room temperature, the nickel foam was removed, washed with deionized water, and dried to obtain CoFe-C. i @GQDs / NF.
[0039] The above CoFe-C i The @GQDs / NF electrocatalyst electrode, when subjected to a voltage of 2.0V vs. RHE in a 1M KOH + 0.5M NaCl solution, achieved a working current of 1.2A and could operate stably for 100 hours without any decrease in current.
[0040] Example 2
[0041] Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O, and urea were dissolved in 60 mL of deionized water and stirred to form a transparent solution. The concentrations of Co(NO3)2·6H2O were 2 mM, Fe(NO3)3·9H2O were 1.5 mM, and the Co / Fe atomic molar ratio was 1.33; the concentrations of Na3C6H5O7·2H2O were 0.5 mM, and the urea concentration was 5 mM. The transparent solution was transferred to a 100 mL hydrothermal reactor, and a cleaned and dried 1 cm × 2 cm piece of nickel foam was added. The reactor was placed in an oven and kept at 120 °C for 10 h, then allowed to cool naturally to room temperature. The sample was rinsed with distilled water and then dried under vacuum at 60 °C. 1 mL of the LGQDs solution was diluted with deionized water to 20 mL, transferred to a 50 mL hydrothermal reactor, and the dried sample was added. The hydrothermal reactor was placed in an oven at 150°C for 3 hours. After cooling to room temperature, the nickel foam was removed, washed with deionized water, and dried to obtain CoFe-C. i @GQDs / NF.
[0042] The above CoFe-C i The @GQDs / NF electrocatalyst electrode, when subjected to a voltage of 2.0V vs. RHE in a 1M KOH + 0.5M NaCl solution, achieved a working current of 1.2A and could operate stably for 100 hours without any decrease in current.
[0043] Example 3
[0044] Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O, and urea were dissolved in 60 mL of deionized water and stirred to form a transparent solution. The concentrations of Co(NO3)2·6H2O and Fe(NO3)3·9H2O were 2 mM, with a Co / Fe atomic molar ratio of 1. The concentrations of Na3C6H5O7·2H2O were 0.6 mM, and the concentration of urea was 5 mM. The transparent solution was transferred to a 100 mL hydrothermal reactor, and a cleaned and dried 1 cm × 2 cm piece of nickel foam was added. The reactor was placed in an oven and kept at 120 °C for 10 h, then allowed to cool naturally to room temperature. The sample was rinsed with distilled water and then dried under vacuum at 60 °C. 1 mL of the LGQDs solution was diluted with deionized water to 20 mL, transferred to a 50 mL hydrothermal reactor, and the dried sample was added. The hydrothermal reactor was placed in an oven at 150°C for 3 hours. After cooling to room temperature, the nickel foam was removed, washed with deionized water, and dried to obtain CoFe-C. i @GQDs / NF.
[0045] The above CoFe-C iThe @GQDs / NF electrocatalyst electrode, when subjected to a voltage of 2.0V vs. RHE in a 1M KOH + 0.5M NaCl solution, achieved a working current of 1.2A and could operate stably for 100 hours without any decrease in current.
[0046] Example 4
[0047] Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O, and urea were dissolved in 60 mL of deionized water and stirred to form a transparent solution. The concentrations of Co(NO3)2·6H2O and Fe(NO3)3·9H2O were 2 mM, with a Co / Fe atomic molar ratio of 1. The concentrations of Na3C6H5O7·2H2O were 0.5 mM, and the concentration of urea was 5 mM. The transparent solution was transferred to a 100 mL hydrothermal reactor, and a cleaned and dried 1 cm × 2 cm piece of nickel foam was added. The reactor was placed in an oven and kept at 120 °C for 10 h, then allowed to cool naturally to room temperature. The sample was rinsed with distilled water and then dried under vacuum at 60 °C. 1 mL of the LGQDs solution was diluted with deionized water to 20 mL, transferred to a 50 mL hydrothermal reactor, and the dried sample was added. The hydrothermal reactor was placed in an oven at 150°C for 3 hours. After cooling to room temperature, the nickel foam was removed, washed with deionized water, and dried to obtain CoFe-C. i @GQDs / NF.
[0048] Scanning electron microscope image as follows Figure 1 As shown, the prepared LDH nanosheets exhibit serrated edges and have more edge adsorption sites.
[0049] Transmission electron microscope image as shown Figure 2 As shown, GQDs were successfully loaded onto CoFe-C. i surface.
[0050] The above CoFe-C i The @GQDs / NF electrocatalyst electrode, when subjected to a voltage of 2.0V vs. RHE in a 1M KOH + 0.5M NaCl solution, achieved a working current of 1.2A and could operate stably for 100 days without a decreasing trend in current.
[0051] Linear sweep current-voltage (LSV) curve as shown Figure 3 As shown, CoFe-C i @GQDs / N exhibits excellent OER performance. CoFe-C i The OER activity of the @GQDs / NF electrode is slightly higher than that of CoFe-C. i / NF is far superior to RuO2 and NF electrodes. It only requires an overpotential of 255mV to generate 100mAcm. –2 The current density.
[0052] Stability test curves are as follows Figure 4 As shown, CoFe-C i @GQDs / NF can operate stably for 100 days at an ultra-high current of 1.2A.
[0053] The above are merely embodiments of the present invention and do not limit the scope of the patent. Any equivalent modifications made based on the content of this specification, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.
Claims
1. A method for preparing an ultra-stable electrocatalyst capable of electrolyzing seawater at ampere-level currents, characterized in that, The electrocatalyst comprises a conductive substrate of nickel foam, CoFe-LDH for providing active sites, and GQDs supported on LDH; The method includes the following steps: 1) Dissolve Co(NO3)2·6H2O, Fe(NO3)3·9H2O, Na3C6H5O7·2H2O and urea in deionized water and stir to form a transparent precursor solution; wherein, the molar ratio of Co / Fe metal atoms is 0.7 ~ 1.4; the total content of Co and Fe metal ions in the precursor solution is controlled at 3.5-4.5 mmol / L; 2) Transfer the transparent solution from step 1) to a hydrothermal reactor, add clean and dry nickel foam, carry out the first thermal synthesis reaction, and then allow it to cool naturally to room temperature; 3) Rinse the sample obtained in step 2) with distilled water and then dry it; 4) Dilute the GQDs solution with deionized water, transfer it to a hydrothermal reactor, add the sample obtained in step 3), and carry out a second thermal synthesis reaction. After cooling to room temperature, wash and dry to obtain the electrocatalyst CoFe-C. i @GQDs / NF; In step 1), the concentration of Co(NO3)2·6H2O in the precursor solution is 1.5-2.5 mmol / L; In step 1), the concentration of Fe(NO3)3·9H2O in the precursor solution is 1.5-2.5 mmol / L; In step 1), the concentration of Na3C6H5O7·2H2O in the precursor solution is 0.4-0.6 mmol / L; In step 1), the urea concentration in the precursor solution is 4-6 mmol / L; In step 2), the first thermal synthesis reaction is carried out at 120 °C for 10 hours. In step 4), the dilution method for graphene quantum dots is as follows: each 1 mL of 1 mg / mL GQDs solution is diluted with deionized water to 20 mL; In step 4), the reaction temperature of the second thermal synthesis reaction is 150 °C and the reaction time is 3 hours.