Preparation Of High Entropy Nanomaterials By Electrospinning And Its Electrocatalytic Performance For Water Splitting In Alkaline Media

The development of renewable energy is expected to solve the environmental problems and energy shortage caused by the excessive consumption of traditional fossil energy.Especially,hydrogen energy has attracted much attention due to its advantages such as high combustion heat value,and sustainability.Among many hydrogen production methods,electrolytic water hydrogen production technology can provide high-purity hydrogen resources quickly.The key to hydrogen production by electrolysis of water is to develop highly active and stable catalysts to reduce the cell voltage.In the past,the traditional metal alloys and their compounds lack of effective methods to control their chemical composition and electronic structure due to the limited kinds of elements.High entropy nanomaterials have become a hot topic in the research of catalysts for hydrogen production from electrolytic water due to their rich composition,controllable electronic structure,and excellent structural stability.Thus,a series of high entropy nanostructured catalytic materials have been prepared by combining electrospinning technology with high-temperature reduction methods.The chemical composition and stoichiometric ratio of high entropy alloys（HEA）and high entropy sulfides（HES）were designed to regulate their chemical and electronic structures,establishing a structure-activity relationship between high entropy nanostructures and the performance of electrolytic water,and further revealing their reaction mechanism through density functional theory calculations（DFT）.The main contents are as follows:（1）A new method of electrospinning and high temperature thermal reduction was developed to prepare high entropy alloy.Fe Co Ni Cr based high entropy alloy nanoparticles were synthesized during high-temperature pyrolysis using electrospun nanofibers as a uniformly mixed carrier of multiple elements and the confinement effect of carbon nanofibers.The effects of thermal reduction temperature,metal composition,and the type of the fifth element on the microstructure,crystal structure,and electrocatalytic hydrogen evolution reaction activity of composite materials were investigated.The results showed that the Fe Co Ni Cr Ir/CNFs prepared at 1000℃had the best activity and stability.The overpotential for HER was only 42 m V at 10 m A cm^-2current density in 1 M KOH electrolyte,lower than that of commercial Pt/C.The synergistic effect between the multi-metal components significantly improves the catalytic activity of nanocrystals.Besides,the unique high entropy mixing state of high entropy alloys and the carbon layer coated on the surface of nanoparticles simultaneously endow the high entropy alloy catalyst with excellent stability.（2）A high entropy atom regulation strategy dominated by electronegativity was proposed,transforming inactive sites into electron rich active sites.Similarly,according to the above method,Fe Co Ni Cu Mn high entropy alloy nanocrystals on carbon nanofibers were prepared by combining low electronegativity Mn and high electronegativity Cu with structural metals Fe,Co,and Ni.And total water electrolysis properties in alkaline media were investigated.In1 M KOH electrolyte,Fe Co Ni Cu Mn/CNFs provided 281 m V of HER low overpotential(current density of 100 m A cm^-2)and 386 m V of OER low overpotential(current density of200 m A cm^-2).Physical representation has demonstrated that strong local electron interactions between multiple metal sites are caused by differences in electronegativity,which increases the local electron density of Ni and Cu sites,and decreases the local electron density of Fe,Co,and Mn sites.In addition,DFT calculations and in-situ Raman show that electron-rich Cu sites are driven by redistribution of electron density between elements to act as active sites for water electrolysis.Therefore,the adsorption energy barrier between the high entropy alloy and the reaction intermediate is effectively reduced,and the electrocatalytic activity of HEA is increased.（3）Considering that non-metallic sulfur element has higher electronegativity than general transition metals,the sulfur atom is further introduced to mix with various metals to form a solid solution structure.High entropy sulfide nanoparticles were successfully synthesized in situ on carbon nanofibers.Using electrospun nanofibers as the carrier,five common transition metals（Fe,Co,Ni,Cr,and Mn）and sulfur sources were introduced through impregnation,and further combined with the Joule pyrolysis method with rapid temperature rise and fall characteristics.The optimal electrocatalytic performance was explored by controlling the synthesis temperature of HES.The results showed that the HES prepared at 1600℃exhibited the best OER catalytic activity in alkaline media.The overpotential was only 320 m V at the current density of 50 m A cm^-2,and its performance was superior to that of most sulfide catalysts.The high entropy sulfide prepared after the introduction of S element forms a more complex crystal structure（M₉S₈）,and the synergistic catalysis between various metal atoms and sulfur element significantly enhances OER activity.