Regulation Of Electrocatalytic Properties Of Co Based Self-supporting Materials By Surface/Interface Engineering

Electrochemical water splitting is considered the most attractive technology for storing renewable electricity in the form of hydrogen fuel.However,the complex reaction and slow kinetic behavior of anodic oxygen evolution reaction（OER）and cathodic hydrogen evolution reaction（HER）at the three-phase interface limit the practical application of water electrolysis technology.Compared with traditional powder catalysts,self-supported electrocatalysts can expose more active sites due to their three-dimensional structure,avoid the electron transfer problems caused by the binder required for powder catalysts,and improving the load and stability of catalytic materials at the same time.Therefore,how to improve the surface activity of self-supporting materials is a new problem for it’s development and application.Current studies indicate that surface/interface engineering can effectively improve the electronic structure,electron transfer capacity and electron density of active sites of materials,providing a feasible way to improve the catalytic activity.In this paper,carbon cloth supported transition metal self-supporting materials were prepared and further treated by different surface/interface treatment methods,which successfully improved the electrocatalytic activity of the materials.After surface/interface treatment,the catalytic materials have lower overpotential,Tafel slope,excellent stability and active specific surface area.As a new type of carbon material,carbon dots are used as zero-dimensional conductive materials to load metals in the preparation of catalytic materials.The first work of this paper takes full advantage of the large number of functional groups on the surface of carbon dots and their ability to control the electron valence state of transition metals.The shell surface morphology of the materials was regulated during the preparation of core-shell structure self-supporting catalytic materials.TEM characterization proved the formation of rough disordered sheet structure.The overpotential of OER increased by 33 m V at 10 m A cm^-2 current density,and the slope of Tafel decreased from 226.7 m V dec^-1 to 147.5 m V dec^-1.After 50 h operation,the electrochemical property still remains about 75%.In the following work,we also used Co based transition metal oxides as a template,and NaBH₄ was used to construct a crystalline-amorphous interface on the surface of the material,and regulated the degree of amorphization.The construction of the crystalline-amorphous interface on the surface of CoFe-Co₃O₄/CC not only regulates the valence state of transition metals,but also increases the exposure of the active sites of the material.The HER performance of the material is improved by 134 m V at a current density of 20m A cm^-2.The OER performance is improved by 31 m V at a current density of 10 m A cm^-2,and has a smaller Tafel slope and impedance.The formation of the crystalline-amorphous interface changes the overall valence state of the transition metals,causing Co to shift to the high-energy band and improving the overall catalytic performance of the material.The Co-based self-supporting catalytic material after surface/interface treatment has lower overpotential,Tafel slope,excellent stability and active specific surface area,and the characterization of the material explains the performance improvement of the catalyst after different surface/interface treatment.The reasons provide some guidance for the rational design and preparation of catalysts in the future.