Controllable Preparation And Electrochemical Water Splitting Of Non-noble Metal High-entropy Alloy

The growing energy crisis and environmental pollution have attracted global attention,so it is extremely necessary to develop renewable and clean emerging energy alternatives to traditional fossil fuels.Hydrogen is an ideal energy carrier and has attracted wide attention because of its high energy density and green recycling of combustion products.Electrochemical water splitting is a clean and practical hydrogen production technology,which can be combined with renewable energy sources to produce"green hydrogen".Electrochemical water splitting mainly includes the hydrogen evolution reaction（HER）of the cathode and the oxygen evolution reaction（OER）of the anode and the catalyst plays a key role in the above processes.Among those that have received much attention are the noble metal based electrocatalysts,which possess higher intrinsic activity,but can not be widely used due to the limitations of reserves and cost.Therefore,it is particularly important to explore the non-noble metal based electrocatalyst to replace the noble metals for the water splitting reaction.However,these catalysts generally have no more than three elements.To some extent,the limited and simple alloy composition hinders the development of certain special properties.Therefore,it is important to explore unconventional alloy electrocatalytic systems.High-entropy alloys are emerging multi-component alloys that offer great possibilities for the design of electrocatalysts（especially multifunctional electrocatalysts）due to their variable elemental composition.Compared with traditional alloys,high entropy alloys have a series of advantages in structure and properties.Therefore,we focus on the controllable preparation process of non-precious metal electrocatalytic material and its application in water decomposition.The specific study content includes the following two parts:1.Multicomponent intermetallic nanoparticles on hierarchical metal network as ultrahigh-current-density catalysts for highly efficient water splitting.Different from the multimetallic solid-solution nanocatalysts that usually encounter elemental partition and are thermodynamically prone to coarsen via atom diffusion with a low barrier energy,the intermetallic compound nanocatalysts（ICC）are of strong covalent bonds to significantly suppress interatom diffusion and interparticle aggregation,enabling a higher thermodynamic/kinetic stability in harsh electrochemical environments.Nevertheless,it always remains a grand challenge in further improving the intrinsic activity of ICCs because of poor adjustability caused by their well-defined stoichiometry and ordered atomic structure.Based on the above considerations,we prepared multicomponent intermetallic Mo（Ni Fe Co）₄nanoparticles seamlessly integrated on hierarchical nanoporous Ni skeleton（Mo（Ni Fe Co）₄/Ni）by facile and scalable alloying/dealloying procedures as robust electrocatalysts for alkaline HER.Fe and Co atoms partially and randomly substituting Ni sites in intermetallic Mo Ni₄matrix to form a high-entropy Ni Fe Co sublattice in Mo（Ni Fe Co）₄gives rise to versatile electroactive sites for accelerating dissociation of water and mediating adsorption/combination of H*.The hierarchical nanoporous Ni skeleton as current collector electrically contacts with electroactive Mo（Ni Fe Co）₄via coherent Mo（Ni Fe Co）₄/Ni interfaces and facilitates simultaneously electron transfer and H₂O/OH^-transportation to reach the electroactive sites for hydrogen generation.It can reach ultrahigh current density of～2300 m A cm^-2at a low overpotential of 200 m V,with the low Tafel slope of～35 m V dec^-1and long-term stability in 1 M KOH electrolyte.When assembled with its electrooxidized and nitrified derivative as the anode for oxygen-evolution reaction,the AWE based on nanoporous Mo（Ni Fe Co）₄/Ni can operate at a low voltage of～1.579 V to deliver 100m A cm^-2,along with a long-term stability.2.Nanoporous nonprecious high-entropy alloys as multi-site electrocatalysts for hydrogen evolution reactionTo further extend the application of Ni-based materials in the field of HER,we prepared self-supported nanoporous high-entropy Ni Fe Co Cu Ti alloy by a facile and scalable alloying/dealloying strategy as an efficient and robust nonacidic HER electrocatalyst.Therein,surface alloy of multicomponent Ni Fe Co Cu Ti serves as multi-site electroactive center to accelerate water dissociation and mediate combination of H*into H₂by virtue of distinct adsorption behaviors of H*and OH*on Ni Fe Co Cu and Ti components.Owing to column-nanostructured nanoporous architecture that enlists electroactive Ni Fe Co Cu Ti sites to be highly accessible while facilitating electron transfer and mass transportation,the self-supported nanoporous high-entropy Ni Fe Co Cu Ti alloy exhibits superior alkaline HER electrocatalysis.It can reach ultrahigh current density of 2 A cm^-2at a low overpotential of 209 m V,with the low Tafel slope of～43 m V dec^-1and exceptional stability for 240 hours in 1 M KOH electrolyte.While in 1 M buffer electrolyte（p H=6.9）,it can deliver current density of 100 m A cm^-2at the overpotential of 159 m V.These impressive HER electrochemical properties make it promising candidate electrode material in water electrolysis for large-scale hydrogen production.