Preparation Of Self-supported Electrocatalyst For Alkaline Oxygen Evolution Reaction And Its Application In Anion Exchange Membrane Water Electrolyzers

Hydrogen production by electrolysis of water from renewable energy is an ideal way to obtain hydrogen energy.At present,there are two main technologies for hydrogen production by electrolysis of water:alkaline water electrolyzers（AWE）and proton exchange membrane water electrolyzers（PEMWE）.AWE can utilize non-noble metal catalysts but suffer from slow response,low operating current density and high energy consumption.PEMWE has the advantages of fast response,high current density,and low energy consumption,but the scarcity and expensiveness of the noble metal catalysts limit the large scale development of PEMWE.Anion exchange membrane water electrolyzers（AEMWE）combines the advantages of AWE and PEMWE.In addition to high current density and low energy consumption,inexpensive and abundant non-noble metal catalysts can be used,which is attracting more and more attention of researchers and AEMWE is expected to become an important way of industrial hydrogen production in the future.However,for the high working current density of AEMWE,the catalysts used by AWE cannot meet the requirements.This paper focuses on AEMWE devices and suitable anode catalysts.Taking transition metal nickel-iron hydroxide as the research object,using metal element doping and increasing the electrochemical active surface area to improve its catalytic activity and stability.A high-performance self-supported alkaline oxygen evolution reaction（OER）electrocatalytic material was prepared,and further assembled into a membrane electrode assembly for AEMWE test.By optimizing the device and operating conditions,excellent water electrolysis performance was obtained.The specific contents are as follows:（1）High-performance self-supported alkaline OER catalysts were prepared.A layer of nickel-iron alloy cauliflower array Ni Fe/NF was grown in situ on nickel foam by electrodeposition method.By changing the ratio of nickel-iron in the electroplating solution,the alkaline OER activity of the plating precursors with different nickel-iron ratios was explored.It was found that when the molar ratio of nickel-iron in the plating solution was 1:1,the OER performance was the best and taking it as a precursor to convert into nickel-iron hydroxide Ni_xFe_yOH/NF by nickel salt etching with hydrothermal method.Nickel-iron flower arrays with different etching degrees were obtained by adjusting the amount of nickel salt and the cauliflower array was successfully etched into a flower array,which further increased the surface area of the catalyst and improved its activity.The optimized Ni_xFe_yOH-1Ni/NF catalyst exhibits excellent OER electrocatalytic activity and stability.The OER performance of the prepared samples was tested and it required only 285 m V overpotential to drive current density of 500 m A·cm^-2 in 1 M KOH with Tafel slope of 58m V·dec^-1.After 50 h of chronopotentiometry at this current density,the required potential hardly changed,showing high stability.（2）A high-performance AEMWE water electrolysis device was constructed using the prepared self-supported OER catalyst.Optimized AEMWE membrane electrode structure and the structure of membrane electrode assembly was determined with nickel foam self-supported catalyst as both anode catalyst and gas diffusion layer,cathode powder catalyst coated on anion exchange membrane（CCM）,and carbon paper as cathode gas diffusion layer.From the perspective of optimizing contact resistance,the anion exchange membrane water electrolysis device was designed and assembled,the connecting device was optimized,and the electrolytic cell test platform was built.The research has obtained the mature preparation process of membrane electrode assembly with compact structure,no leakage and no membrane penetration when the gas diffusion layer of the cathode and anode is 20-50μm thinner than the gasket on the same side and the installation torque is 3.2 N·m by the direct superposition method.The performance of AEMWE was improved by optimizing the electrolyte flow rate,electrolyte temperature,and electrolyte p H.Finally,the self-supported OER catalytic layer was used to assemble the AEMWE water electrolysis device.At 60℃and 1 M KOH,the applied potential required for 500 m A·cm^-2 was only 1.64 V.After 100 h stability test,the performance is only reduced by 30 m V,showing excellent water electrolysis performance,and its performance is better than that of AEMWE using Ir O₂catalyst at the OER end,and has certain industrial application potential.