Synthesis And Electrocatalytic Performance Of Tungsten Nitride Nanorods/Graphene Composite Electrode Materials

Alkaline Fuel Cells?AFC?have been attracting increasing attention because a lot of advantages such as small size,light weight,low operating temperature,low heat loss,etc.which made it very suitable to be a power source for automobiles or portable electrical appliances.In AFC,the dynamics of the Oxygen Reduction Reaction?ORR?occurring on the cathode material largely determines the efficiency of the cell.In the current AFC,the noble metal Pt catalyst has the highest oxygen reduction efficiency and is the most widely used,however,the high price and inadequate storage limited its range of application.Therefore,it is highly significant and application valued to develop the inexpensive non-precious metal catalysts that can replace Pt in whole or in part to reduce the cost of AFC,maintain or enhance the catalytic of electrode materials and ultimately achieve the industrialization of AFC.As a novel carbon material with unique structure and a series of excellent physical and mechanical properties,graphene is an ideal catalyst carrier for reducing the overpotential of oxygen reduction reaction,increasing the reaction current density and improving the fuel conversion efficiency.The surface electronic structure of the transition metal nitride is similar to that of Pt,and has the catalytic activity of a platinum group-like metal and is known as a"quasi-platinum catalyst."In this thesis,the author combined several synthetic methods to obtain a tungsten nitride nanorods/graphene composite structure.Subsequently,the loading of Pt and PtNi alloy nanoparticles with low content on the surface of the composite structure was performed,and the ORR activity of various composite structures was systematically compared.The results of the research were as follows:?1?Graphene oxide nanosheets with uniform morphology and uniform size was obtained by the modified Hummers method.Then WO₃ nanorods/GO nanosheet composites structures were synthesized by solvothermal method.The microstructure and surface chemical state were characterized.Electrochemical tests showed that the complex has oxygen reduction activity.?2?The WO₃ nanorods/GO nanosheet composite structure was modified by Chemical Vapor Deposition?CVD?,and the tungsten nitride/reduced graphene oxide composite structure was successfully obtained.X-ray diffraction,scanning electron microscopy,and high-resolution transmission electron microscopy data indicate that the composite structure consists of W₂N nanorods uniformly grown on reduced Graphene Oxide?rGO?nanosheets.The ORR results show that the nitrided composite structure is shifted from0.6V to 0.71V,and the limiting current density is 1.4 times that before the nitridation.Electrocatalytic performance significantly improved?3?The Pt modification of W₂N nanorods/rGO nanosheet composites was performed by chemical bath method.X-ray diffraction,scanning electron microscopy and high-resolution transmission electron microscopy data show that the composite structure consists of Pt nanoparticles loaded on the composite structure of W₂N-rGO.The ORR electrochemical measurements of the composite structure showed that the limiting current density was 7.1 mA cm^-2,which was increased compared to Pt/C;the half-slope potential was shifted from 0.63V of the 0.69V compared to W₂N-rGO composite,indicates that the electrocatalytic performance has been significantly improved.?4?Using the formic acid reduction method,the W₂N nanorods/rGO nanosheet composite was modified by PtNi alloy,and the W₂N-rGO/PtNi composite was successfully obtained.Through various characterization methods,the composite structure is composed of PtNi alloy supported on the composite structure of W₂N-rGO.The ORR electrochemical measurements of the composites show that the composites have overall performance over commercial Pt/C catalysts,and the Electrochemically Active Surface Area?ECSA?of the composite is 58.6 m²/g,which was increase by 0.5m²/g compared to the Pt/C catalyst.The half-slope potential of the composite was 0.9 V,which was shifted by 0.05 V compared to the Pt/C catalyst.The limiting current density of the composite was 7.2 mA cm^-2,which was greater than the 6.9 mA cm^-2 of the Pt/C catalyst.By comparing these performance indicators,it was found that W₂N-rGO/PtNi surpassed the Pt/C catalyst in these indicators.