Fabrication Of Liquid-exfoliated Graphene Based Nanocomposites In Supercritical Fluid And Their Electrochemical Performance

As a unique 2-D carbon nanomaterial,graphene is well-known for its large specific surface area,excellent chemical stabilty,high mechanical strength and electrical conductivity.Its exceptional features hold great promise as a substrate for decoration of active nanomaterials to render them highly electrically conductive to the current collectors.In this dissertation,nickel hydroxide,cobalt phosphide and nickel phosphide nanoparticles were loaded on pristine graphene sheets and their electrochemical performance was explored.The specific research contents are as follows:1.Firstly,the pristine graphene was obtained by liquid-phase exfoliation method in a NMP solution.By taking advantage of unique features of supercritical carbon dioxide such as surface tension close to zero,strong penetration capacity and low viscosity,nickel hydroxide nanoparticles were uniformly supported on the inert surface of large surface area graphene.In comparison,other carbon(carbon black and reduced graphene oxide)-based nickel hydroxide composites were prepared in the same experimental conditions.The structural characteristics and chemical composition of nickel hydroxide/graphene nanocomposites were analyzed by XRD,TEM,Raman and XPS,respectively.Electrochemical analysiss(CV,GCD,EIS)was used to characterize the capacitive properties of the nanocomposites and other relevant factors.The graphene-based composites show ultra-high capacitance and excellent stability.2.The cobalt phosphide nanoparticle/graphene composite was synthesized under high temperature conditions by a two-step reaction process.The cobalt phosphide particles were uniformly supported on the graphene sheet by using supercritical fluid.Meanwhile,cobalt phosphide/graphene composites were prepared at different temperatures and compared with composites based on different carbon.The cobalt phosphide/graphene nanocomposites were characterized by XRD,TEM,XPS etc.The hydrogen evolution properties of the composites and related influencing factors were characterized by electrochemical methods(LSV,Tafel slope,EIS,CV).Cobalt phosphate/graphene composites exhibit excellent hydrogen evolution performance in hydrolysis.3.Using supercritical carbon dioxide,nickel phosphide nanoparticle/graphene composites were synthesized by one-step reaction at high temperature.Nickel phosphide/graphene composites were also prepared at different temperatures and compared with composites based on other carbon substrate.The structural characteristics of the nickel phosphide/graphene nanocomposites were analyzed by XRD and TEM.Electrochemical methods(CV,GCD,EIS)were used to characterize the hydrogen evolution performance of the composites.The nickel phosphide/graphene composites show excellent hydrogen evolution efficiency and stability under acidic conditions.