Engineering,regulating And Behavior Of High-Entropy Alloy Catalyst For Oxygen Evolution Reaction

High-entropy alloy is a novel alloy material composed of more than four principle elements,and its high entropy configuration,defect-rich and synergistic characteristics endow it with superior physicochemical properties than conventional alloys.In this paper,a series of bulk transition metal-based high-entropy alloys have been prepared by simple metallurgical methods to investigate their OER performance.The content of this paper is divided into three main parts as follows:1.First,the OER overpotential of the transition metal-based Fe Co Ni Cu Cr HEAs catalysts is predicted using a first-principles approach.The theoretical prediction results show that the theoretical overpotential of the Fe Co Ni Cu Cr HEAs in alkaline solution achieves 425 m V,indicating that the HEA possesses good catalytic potential.Then,based on the theoretical predictions,the bulk Fe Co Ni Cu Cr and Fe Co Ni Cu Cr Al are prepared by a simple metallurgical casting method and formed into HEA films by magnetron sputtering on a carbon cloth substrate to explore their OER catalytic properties.It is found that the Fe Co Ni Cu Cr Al HEA exhibit the best catalytic performance among all samples,which shows good catalytic properties such as 270 m V overpotential and 46 m V dec^-1 Tafel slope at a current density of 10 m A cm^-2 in 1 M KOH solution and long-term stability up to 50hours.This study embodies the significance of theory guided experiments and provides ideas for designing HEAs with excellent catalytic performance.2.Thirty-five HEA bulk electrodes containing oxide microdomains are prepared by a simple arc smelting technique combined with oxygen microalloying method,and the prepared H（M）EA samples are characterized and analyzed for their physical phase structure,microstructure,and surface electronic states.The XRD characterization results show that（Cr Fe Co Ni Mn）_100-xO_x、（Cr Fe Co Ni）_100-xO_x、（Cr Fe Co Ni Cu）_100-xO_x、（Fe Co Ni）_100-xO_x、（Cr Fe Ni）_100-xO_x、（Cr Co Ni）_100-xO_x are an FCC structure,while Cr Fe Co belongs to the BCC and FCC and intermetallic compound mixed phases;SEM and TEM images demonstrate the oxide microdomain structure and components inside the HEA electrode and the interface between the oxide microdomains and the substrate.In particular,it is determined that the composition of the black particles present in the matrix of the high-entropy alloy is mainly Cr₂O₃.Cr₂O₃ formation is attributed to two aspects,on the one hand,due to the substitution reaction between the micro-alloyed（Co₃O₄）and Cr at high temperature during the preparation of the sample.On the other hand,since Cr is less electronegative than Fe,Co,and Ni,Cr is more oxygenophilic than the other elements.In addition,the electronic state analysis of the as-cast HEA before catalysis by XPS reveals that the metal binding energy of the 4-element HEA system is higher overall than that of the 3-element and 5-element systems,indicating that the 4-element HEA has a higher potential energy with a lower potential barrier,and it is relatively easier for the catalytic reaction to occur.This provides direct clues and evidence for the subsequent exploration of the influence of oxide microdomains on catalytic performance.3.A series of oxide microdomain HEA（O-HEA）integrated electrodes are obtained to explore their OER catalytic activity with atomic level design.It is found that the（Cr Fe Co Ni）₉₇O₃ O-HEA delivers an overpotential of 196 m V at a current density of 10 m A cm^-2,a Tafel slope of 29 m V dec^-1,and a stability of more than 120 h,which is superior to the catalytic performance of the currently reported bulk OER materials.It is found that Cr₂O₃ microdomains are the key to improve the catalytic activity of OER.i)Cr₂O₃microdomain formation in the solid solution changes the local coordination environment of the HEA matrix;ii)Cr ion leaching promotes the effective charge transfer in the electrocatalytic process;iii)Cr ion leaching causes interfacial reconstruction and amorphization.The formation of oxide microdomains by oxygen micro-doped high entropy alloy（O-HEA）can remarkably improve the electrode OER catalytic performance.In this thesis,a series of HEAs catalysts with comparable properties to noble metal catalysts are developed and prepared by means of theoretical prediction,oxygen microalloying,modulate,and enhance the catalytic performance of HEAs OER.These modulation means provide new ideas and directions for the design of catalysts with high activity,stability,and conductivity with industrial applications.