Study On Preparation Of FeCoNiMo High Entropy Alloy Catalysts And Their Oxygen Evolution Performance

Hydrogen production by electrolysis of water is one of the attractive means to realize the hydrogen economic cycle and solve environmental pollution and energy problems.The anodic oxygen evolution reaction（OER）during water electrolysis is a multi-proton coupled process with slow kinetics,which is the key to restricting the efficiency of hydrogen production from water splitting.Therefore,the development of low-cost,high-efficiency,stable and non-noble metal catalysts to replace commercial noble metal-based catalysts（such as Ir O₂ and Ru O₂）is of great significance for expanding the application of hydrogen energy.In recent years,the wide range of compositional modulation and inherently complex surface electronic structure of transition metal-based high entropy alloys provide the possibility to obtain a nearly continuous distribution of adsorption energy curves.Therefore,simultaneous improvement of catalytic activity,selectivity and stability can be achieved by adjusting alloy composition to optimize the adsorption energy.In this paper,the transition metal-based FeCoNiMo high entropy alloy is taken as the research object,efficient and stable electrocatalytic oxygen evolution materials were prepared through composition design and process control,what’s more,the effects of their composition,electronic structure,and surface morphology on their catalytic oxygen evolution performance were studied.This paper mainly studies the following contents:Firstly,a series of FeCoNiMo high entropy alloy spherical powders are prepared in batches by the gas atomization method,and the effect of dealloying process on the catalytic activity and stability of the alloy powders was analyzed.It is found that the alloy powder prepared had a single-phase face-centered cubic solid solution structure,and the alloy powder had the best performance after 28 h of dealloying treatment.In 1 M KOH solution,the catalyst only need an overpotential of 271 m V to reach a current density of 10 m A/cm²,and the Tafel slope is 48m V/dec.The uniform metal oxygen（hydroxide）layer formed in situ on the surface of the powder matrix during the dealloying process provides abundant active sites,and forms a core-shell structure with the high entropy alloy matrix with good electrical conductivity,which improves the OER activity and stability of the catalyst.Secondly,a series of FeCoNiMoO nanoparticles are prepared in by supersaturated co-precipitation method to further optimize the OER catalytic performance of FeCoNiMo high entropy alloys.In 1 M KOH solution,the catalyst Fe Co Ni₃Mo_0.3O only need an overpotential of 231 m V to reach a current density of 20 m A/cm²and the Tafel slope is 65 m V/dec.It is found that the appropriate amount of Mo element doping enables the nanoparticles to obtain a large specific surface area and abundant oxygen vacancy defects.The large surface area increases the number of active sites,while oxygen vacancy defects can optimize the surface adsorption energy of the catalyst,thereby lowering the OER reaction energy barrier and obtaining the best OER activity.After 40 h OER test,the overpotential did not increase significantly,the surface morphology of samples were transformed from nano-particles to nano-lamellar sheets,which made the catalyst have excellent cycle durability.Thirdly,the AlFeCoNiMo high-entropy alloy ribbons are prepared by the melt rapid quenching method,and its active surface area was increased by a dealloying process to obtain a self-supporting catalyst.The Al FeCoNiMo high-entropy alloy is composed of a face-centered cubic phase and a body-centered cubic phase enriched with Al and Ni elements existing at the grain boundary.The Al Ni body-centered cubic structure with poor corrosion resistance is removed during dealloying process,and a uniformly distributed nanopillar array was formed on the surface.The ribbons obtained the best catalytic activity after dealloying for 15 min.In 1M KOH solution,the catalyst only require an overpotential of 228 m V to achieve the current density of 10 m A/cm²,the Tafel slope is only about 35 m V/dec and after 30 h cycle test,there is only a neligible increase of the overpotential.It is found that the nanopillar array composed of porous structure exposes a large number of catalytic active sites,which accelerates mass transfer and gas diffusion,and the synergistic effect between the elements optimizes the adsorption energy of the active sites for intermediates.