Nickel-graphene nanocomposite with improved electrochemical performance for La0.7Mg0.3(Ni0.85Co0.15)3.5 electrode

Abstract

A Ni-rGO nanocomposite was synthesized by a hydrothermal process and La0.7Mg0.3(Ni0.85Co0.15)3.5, an AB3.5-type hydrogen storage alloy, was prepared by magnetic levitation melting under argon atmosphere. The influences of the Ni-rGO nanocomposite on the hydrogen storage and electrochemical performance of the La0.7Mg0.3(Ni0.85Co0.15)3.5 alloy were investigated via pressure composition isotherms (PCT) and electrochemical measurements. The PCT curves revealed that the addition of the Ni-rGO nanocomposite improved the reversibility of hydrogen absorption and desorption for the La0.7Mg0.3(Ni0.85Co0.15)3.5 alloy. The electrochemical measurements showed that the electrochemical impedance of the La0.7Mg0.3(Ni0.85Co0.15)3.5 alloy electrode was significantly reduced, the high rate dischargeability, HRD1200, increased from 60% to 86%, the limiting current density, IL, increased from 1216.7 mA·g−1 to 2287.6 mA·g−1, and the hydrogen diffusion coefficient, D, increased with the added Ni-rGO nanocomposite. These improvements to the electrochemical performance are mainly attributed to the Ni-rGO framework, with the large specific surface area of the graphene, and to the high conductivity of metal nickel.