Preparation method of nickel-based composite oxygen evolution anode for alkalescent electrolyte

Abstract

The invention provides a preparation method of a nickel-based composite oxygen evolution anode for alkalescent electrolyte. According to the invention, nickel-based alloy is used as substrates, two same substrates are respectively used as a working electrode and an auxiliary electrode, two-electrode system electrochemical oxidation reduction treatment at room temperature is carried out in a mixed solution of phosphate, carbonate and chloride, and two reconstructed nickel-based composite oxygen evolution electrodes are obtained at the same time. In the electrochemical oxidation process, nickel ions and other metal (Fe, Co, Cr and Mn) ions are dissolved out from the nickel-based alloy under the etching assistance of chloride ions; in the electrochemical reduction process, water on the electrode is reduced to form hydroxyl. Under continuous oxidation reduction, substance reconstruction is carried out to generate a composite catalyst layer of phosphate, carbonate and hydroxide of nickel and other metals, so that not only can the oxygen evolution activity be improved, but also metal dissolution and corrosion passivation when the catalyst is used in a weakly alkaline solution can be inhibited, and the durability of the electrode is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of electrolytic hydrogen production technology, specifically to a nickel-based composite oxygen-evolving anode material for weakly alkaline electrolytes and its preparation method. Background Technology

[0002] With increasing energy consumption and environmental pollution, hydrogen energy, as one of the cleanest energy sources on Earth, has become a significant alternative to fossil fuels. Among these technologies, water electrolysis for hydrogen production is relatively mature and environmentally friendly, making it a major direction for future development. However, traditional water electrolysis technologies use strongly alkaline solutions as electrolytes. Compared to water decomposition processes that occur under weakly alkaline conditions, this causes significant corrosion to reactors and pipelines, increasing maintenance costs and reducing safety. Furthermore, using weakly alkaline solutions as electrolytes presents a considerable challenge to the activity and stability of the oxygen evolution electrode.

[0003] Oxides of noble metals ruthenium and iridium are considered the most advanced OER catalysts, but their high cost, limited resources, and poor stability restrict their development and application as oxygen evolution anodes. Nickel-based alloys are favored by researchers due to their abundant resources, good performance, and electronic tunability. Highly active catalysts can be prepared by using nickel-based alloys as substrates for heteroatom doping, vacancy construction, structural design, and composition adjustment. CN201610315447.7 reports a nickel-iron composite oxygen evolution anode prepared by electrodeposition, which has a three-dimensional nanoflower-like structure assembled from ultrathin nanosheets. This structure not only increases the oxygen evolution catalytic active sites on the electrode surface but also facilitates oxygen escape, significantly reducing its oxygen evolution overpotential in weakly alkaline sodium carbonate solution. CN202210496759.8 describes an in-situ growth method where nickel foam is placed in a reactor containing a mixture of ammonium molybdate and nickel nitrate for hydrothermal treatment. The foam is then placed in a potassium ferricyanide solution for ion exchange. Finally, the electrode is placed in a tube furnace and phosphated under an argon atmosphere to obtain a nickel-iron phosphide / nickel molybdate core-shell composite electrode. This method significantly improves electrochemical performance and stability, but its preparation process is complex and has low safety.

[0004] Besides the activity of the oxygen evolution electrode, its stability is also challenged under weakly alkaline solution conditions due to micro-region acidification near the electrode and corrosion passivation during the oxygen evolution process. Therefore, a catalyst structure that can inhibit the dissolution of the base metal and prevent electrolyte corrosion is of great significance for the electrolytic hydrogen production in weakly alkaline solutions. Summary of the Invention

[0005] In response to the above discussion, the present invention provides a simple and efficient nickel-based composite oxygen evolution anode material and its preparation method. The electrode material is characterized by using a nickel-based alloy as a substrate and loading a composite catalyst layer of phosphate, carbonate and hydroxide in situ on the surface, which has excellent activity and stability in weakly alkaline solutions.

[0006] To achieve the above-mentioned objectives, the nickel-based composite anode material is prepared by the following method:

[0007] (1) First, the nickel-based alloy substrate is subjected to ultrasonic pretreatment. First, degreasing is performed using ethanol and acetone for 20-30 minutes; then pickling is performed using 0.1-1M HCl and ultrasonication at room temperature for 3-10 minutes to remove oxides from the substrate surface; finally, pure water is used for ultrasonication for 10-20 minutes.

[0008] (2) Subsequently, in a two-electrode system, using the same nickel-based alloy substrate as the working and auxiliary electrodes, electrochemical treatment was carried out in a mixed solution of sodium phosphate, sodium carbonate, and sodium chloride. The concentrations of phosphate, carbonate, and chloride ranged from 0.01 to 1 M, respectively. The electrochemical treatment employed a square-wave potential method with a voltage range of 1 to 6 V, a cycle number of 20 to 100, and a duration of 10 to 120 s for each waveband.

[0009] (3) The electrode after electrochemical treatment is rinsed with pure water and dried at 70-350℃ for 20-120 min to obtain the nickel-based composite oxygen evolution anode material prepared in this invention.

[0010] The nickel-based alloy substrate is a binary or multi-element alloy of nickel, iron, cobalt, chromium and manganese.

[0011] In this preparation method, sodium phosphate can be replaced by disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, or potassium dihydrogen phosphate.

[0012] In this preparation method, sodium carbonate can be replaced by potassium carbonate, sodium bicarbonate, or potassium bicarbonate. Furthermore, in step (2), only one of sodium phosphate or sodium carbonate can be added, so that in the prepared material, either the phosphate or carbonate serves as the protective component of the composite layer.

[0013] In this preparation method, sodium chloride can be replaced by potassium chloride or ammonium chloride.

[0014] The square wave potential method uses the same positive and negative constant potentials, with an oxidation potential of 1 to 6V and a reduction potential of -6 to -1V, which can simultaneously obtain two identical electrodes.

[0015] In this preparation method, the Ni metal ions and other metals (one or more of Fe, Co, Cr, and Mn) in the catalyst layer originate from the nickel-based alloy itself. During the electrochemical polarization treatment of the nickel-based alloy substrate, phosphate, carbonate, and hydroxide ions undergo surface reconstruction reactions with the metal ions dissolved from the substrate, forming a composite catalyst of phosphate, carbonate, and hydroxide. The metal composite hydroxide improves the oxygen evolution activity of the substrate material, while the sparingly soluble phosphate and carbonate improve the corrosion resistance of the material, inhibit the dissolution of metals from the substrate surface, protect the surface catalyst from electrolyte corrosion, and enhance its stability in weakly alkaline solutions.

[0016] Weakly alkaline solutions can be carbonate solutions, phosphate solutions, and borate solutions.

[0017] The nickel-based composite oxygen evolution electrode material prepared by this invention exhibits excellent stability in weakly alkaline solutions, achieving a current density of 200 mA / cm² at 27°C and 2M KHCO₃. 2 Under these conditions, a long-term stability test of 200 hours was conducted, and there was no significant degradation in electrode performance before and after the test. Attached Figure Description

[0018] Figure 1 The image shows a comparison of linear sweep voltammetry (LSV) of a nickel-based composite oxygen evolution electrode obtained in Example 1 at 27°C in a 0.5 Mk2CO3 / KHCO3 solution with that of a commercial titanium-ruthenium-iridium electrode.

[0019] Figure 2 The nickel-based composite oxygen evolution electrode obtained in Example 1 was tested at 27°C with 2MKHCO3 and a current density of 200 mA / cm². 2 Comparison of LSV before and after a 200-hour long-term stability test under the specified conditions. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0021] Example 1

[0022] Cut the nickel-iron alloy into 1×1cm pieces. 2Small pieces were ultrasonically treated in ethanol and acetone for 15 minutes at room temperature to remove oil, and then washed with pure water to remove residual liquid. Next, they were ultrasonically treated in 1M HCl solution for 3 minutes, and washed with pure water to remove residual liquid. Finally, they were ultrasonically treated in pure water for 15 minutes and then air-dried at room temperature. The previously treated nickel-iron substrates were used as the working electrode and auxiliary electrode, respectively. A square wave potential of ±3V was applied in a mixed solution containing 0.1M sodium phosphate, 0.01M sodium carbonate, and 0.05M sodium chloride, with 20 cycles and each waveband lasting 20 seconds. After the square wave potential treatment, the electrodes were rinsed with pure water and heat-treated at 100℃ for 30 minutes to obtain the nickel-based composite oxygen evolution electrode material.

[0023] The oxygen evolution performance of the nickel-based composite oxygen evolution electrode material prepared in this embodiment was evaluated. For example... Figure 1 As shown, in a 0.5 Mk₂CO₃ / KHCO₃ solution, at 10 mA / cm 2 The overpotential at current density is 340mV, and at 100mA / cm 2 The overpotential at current density is 430 mV, which is better than the 377 mV@10 mA / cm of commercial titanium ruthenium iridium electrodes. 2 and 630mV@100mA / cm 2 .like Figure 2 As shown, after a long-term stability test of 200 hours, the performance retention rate was >98%, and the amount of iron ions dissolved during the long-term stability test was 0.23 ppm, indicating that the nickel-based composite oxygen evolution electrode material prepared in this embodiment exhibits excellent activity and stability in weakly alkaline solutions.

[0024] Example 2

[0025] The nickel-iron-cobalt alloy substrate was cut into 1×1cm pieces. 2 The pretreatment process for the small fragments was the same as in Example 1. The pretreated nickel-iron-cobalt substrates were used as the working electrode and auxiliary electrode, respectively. A square wave potential of ±4V was applied in a mixed solution containing 0.05M sodium phosphate, 0.05M sodium carbonate, and 0.05M sodium chloride, with 30 cycles and each waveband lasting 10 seconds. After the square wave potential treatment, the material was rinsed with pure water and heat-treated at 120°C for 40 minutes to obtain the nickel-based composite oxygen evolution electrode material.

[0026] The oxygen evolution performance of the nickel-based composite oxygen evolution electrode material prepared in this embodiment was evaluated. In a 0.5 M K₂CO₃ / KHCO₃ solution, at 10 mA / cm⁻¹... 2 The overpotential at current density is 350mV, and at 100mA / cm 2 The overpotential at current density is 450 mV, which is better than the 377 mV@10 mA / cm of commercial titanium ruthenium iridium electrodes. 2 and 630mV@100mA / cm 2After a 200-hour long-term stability test, the performance retention rate was >96%, and the amount of iron ions dissolved during the long-term stability test was 0.36 ppm, indicating that the nickel-based composite oxygen evolution electrode material prepared in this embodiment exhibits excellent activity and stability in weakly alkaline solutions.

[0027] Example 3

[0028] This example is a comparative example. The oxygen evolution performance of a pretreated commercial nickel-iron electrode was evaluated in a 0.5 Mk2CO3 / KHCO3 solution at 10 mA / cm². 2 The overpotential at current density is 421mV, and at 100mA / cm 2 The overpotential at the current density was 527 mV. After a long-term stability test of 200 hours, the performance retention rate was approximately 80%, and the iron ion dissolution was 1.34 ppm. Comparing Examples 1 and 2 with this example, it is shown that the nickel-based composite oxygen evolution electrode material prepared by this invention exhibits higher activity and better stability in weakly alkaline carbonates than commercial foamed nickel-iron electrodes. Furthermore, the amount of iron ion dissolution indicates that the catalytic protective layer formed by the material of this invention can inhibit the dissolution of the base metal and the corrosion of the weakly alkaline solution.

[0029] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Various process solutions that are not substantially different from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-based composite oxygen-evolving anode for weakly alkaline electrolytes, characterized by treating a nickel alloy substrate through electrochemical oxidation-reduction in a mixed solution of phosphate, carbonate, and chloride, thereby enabling the in-situ reconstruction and growth of a composite catalytic layer of nickel and other metals (Fe, Co, Cr, Mn) in phosphate, carbonate, and hydroxide at room temperature, forming a nickel-based composite oxygen-evolving anode. This improves its oxygen evolution activity and stability in weakly alkaline solutions and inhibits metal dissolution and corrosion passivation when used as an oxygen-evolving anode. The method for preparing the nickel-based composite oxygen-evolving anode includes the following steps: (1) The nickel-based alloy is subjected to degreasing, pickling and water washing pretreatment in sequence; (2) Using two identical nickel-based alloy substrates as working and auxiliary electrodes, a two-electrode system electrochemical oxidation and reduction treatment is carried out in a mixed solution of phosphate, carbonate and chloride to achieve the dissolution, deposition and reconstruction of nickel and other metals (Fe, Co, Cr, Mn) on the alloy substrate, thereby growing a composite catalytic layer of nickel and other metals (Fe, Co, Cr, Mn) in phosphate, carbonate and hydroxide. This electrochemical process also yields two electrochemically reconstructed nickel-based composite oxygen evolution anodes. (3) After rinsing the obtained electrode clean, it is dried and heat-treated to obtain the final nickel-based composite oxygen evolution anode.

2. The preparation method according to claim 1, characterized in that, The nickel-based alloy substrate is a binary or multi-element alloy of nickel, iron, cobalt, chromium and manganese.

3. The preparation method according to claim 1, characterized in that, The phosphates mentioned include sodium phosphate, potassium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate, and the concentration of the phosphates is 0.01 to 1 M.

4. The preparation method according to claim 1, characterized in that, The carbonates include sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate, and the concentration of the carbonates is 0.01 to 1 M.

5. The preparation method according to claim 1, characterized in that, Chlorides include sodium chloride, potassium chloride, and ammonium chloride, with a chloride concentration of 0.01–1 M.

6. The preparation method according to claim 1, characterized in that, The electrochemical treatment employs a square-wave potential method, where the potentials are constant, with the same positive and negative values. The oxidation potential ranges from 1 to 6 V, and the reduction potential ranges from -6 to -1 V. The number of cycles ranges from 20 to 100, and each cycle lasts from 10 to 120 seconds.

7. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 70–350℃, and the heat treatment time is 20–120 min.

8. The preparation method according to claim 1, characterized in that, In a two-electrode system, the same nickel alloy electrode is used as the working electrode and the auxiliary electrode, respectively. Alternating oxidation-reduction treatment is performed simultaneously to obtain two electrochemically reconstructed nickel-based composite oxygen evolution anodes in one step, thereby improving the preparation efficiency.

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