Porous Transition Metal Phosphides (Sulfides) For Electrocatalytic Hydrogen (Oxygen) Evolution Reaction

Hydrogen is considered to be a clean energy because of its high combustion value and the combustion product is water.Meanwhile,water electrolysis is a convenient and efficient method to obtain pure hydrogen.However,the high overpotential in the process of water electrolysis often results in a great waste of electric energy.Hydrogen evolution reaction?HER?occurs in cathode and oxygen evolution reaction?OER?occurs in anode of electrochemical water splitting.Pt and Pt-based materials are the most effective catalysts for HER.RuO₂/IrO₂ has high activity in OER.Pt,Ru and Ir are rare elements in the earth,their low abundance and high prices limit their application in water electrolysis.Cobalt-based materials are often considered as strong competitor for water electrolysis to replace noble metal materials due to their excellent HER and OER properties.Porous catalytic materials often expose abundant catalytic active sites to materials,which can greatly improve the catalytic performance of catalysts.CoAl-LDH is often used to prepare porous metal oxides and metal derivatives because of its unique layered structure and amphoteric Al element.In this work,CoAl-LDH was converted into porous Co-based transition metal phosphides?sulfides?by alkali etching and chemical conversion for efficient HER and OER.The specific research contents of this work are as follows:?1?We synthesized a porous cobalt phosphide nanosheets on carbon paper?CoP/CP?.Firstly,we synthesize porous nanosheets of metal hydroxides by selectively etching amphoteric Al in CoAl layered double hydroxides on carbon paper?CoAl-LDH/CP?,and then converts it into porous cobalt phosphide nanosheets on carbon paper?p-CoP/CP?by low temperature phosphidation.The unique porous structure has rich edges,which exposes abundant electrochemical active sites.By this simple and convenient method,the porous and plate-like structure of the nanosheets can be well maintained throughout the reaction process.This study provides a new idea for the design of porous metal oxides,hydroxides and their corresponding transition metal derivatives.?2?We reported a method of etching and sulfurization the CoAl-LDH at the same time to synthesize porous and amorphous cobalt hydroxysulfides nanosheets?PA-CoS_x?OH?_y?.The excellent OER performance of PA-CoS_x?OH?_y is mainly attributed to its unique physical structure and electronic structure.In regulating the physical structure,the unique porous and amorphous structures expose abundant marginal active sites and high specific surface area to the catalyst,which can expose more active sites and promote the OER.The synergistic effect between S and OH and the existence of oxygen vacancies in the material can effectively control the electronic structure of the material,and also result in excellent electrocatalytic activity and high stability to the catalyst.This study presents a new and convenient method to optimize the physical and electronic structure of catalysts.