Controlled Synthesis Of High-entropy Metal Oxyhydroxides And Their Catalytic Performance

Increased global warming and the rapid exhaustion of fossil fuels have prompted researchers to develop economical,earth-abundant green energy sources to meet future energy needs.Hydrogen energy is not only clean but also has a high energy density and is likely to become a mainstream energy source in the future.Among all methods of hydrogen production,electrolysis of water is a promising route to achieve sustainable production of hydrogen because of its simplicity,abundance of raw materials,and high availability.The Oxygen evolution reaction（OER）has a high overpotential and low water splitting efficiency due to its very slow kinetics.Therefore,an OER catalyst with high catalytic activity is required to reduce the overpotential to improve the hydrogen production efficiency.Ru O₂ and Ir O₂,although considered superior OER catalysts,are not suitable for industrial applications due to their high price,low availability,and instability.Therefore,there is a need to find inexpensive electrocatalysts with high catalytic activity to increase efficiency and cut the cost of generating hydrogen.In this paper,high-entropy metal hydroxymethoxy compounds is prepared,and high-entropy sulfides were synthesized,with the following main experiments.（1）A class of high-entropy metal hydroxymethoxy compounds is prepared by a one-step solvothermal method.The ion potential rule for synthesizing metal hydroxymethoxy compounds was discovered,which enabled the controlled synthesis of high-entropy metal hydroxymethoxylates.It has been found that Metal ions with a much larger ionic potential than Co²⁺or metal ions with a single ionic valence state and a similar ionic potential to Co²⁺can form high entropy metal hydroxymetallic compounds with Ni Co hydroxymetallic compound.In particular,the activated and stabilized Fe Co Ni Mg Cr hydroxymetallic compound has excellent OER performance with an overpotential of only 291 m V at a current density of 20 m A·cm^-2,a Tafel slope as low as 49.1 m V·dec^-1,and outstanding stability.SEM,FTIR,and XPS revealed that the abundant surface oxygen vacancies trigger reconstruction through the involvement of lattice oxygen oxidation to form active species of hydroxyl oxides.The high-entropy metal hydroxymethoxyl compounds can also be used as precursors of high-entropy oxides.The synthesis method can form high-entropy oxides by low-temperature annealing,which reduces the difficulty of synthesizing traditional high entropy oxides and provides a new idea for synthesizing high entropy metal compounds such as high entropy phosphides,high entropy sulfides,and high entropy selenides.（2）The Fe Co Ni Cr hydroxymetallic compound was vulcanized by the solvothermal method.The Fe Co Ni Cr high entropy sulfide showed excellent OER catalytic performance after vulcanization.The crystalline structure,microstructure,and elemental states of the catalyst were investigated by XRD,SEM,XPS,and other characterization methods.In 1 M KOH solution,the high entropy sulfide has an overpotential of only 349 m V at 50 m A·cm^-2,a Tafel slope of 58.4 m V·dec^-1,and excellent electrochemical stability.As the sulfur atoms provide more active edges for the catalytic reaction,the Fe Co Ni Cr high entropy sulfide has more excellent catalytic performance than Fe Co Ni Cr hydroxymetallic compound.At the same time,the study provides a new idea for synthesizing high entropy sulfides.