Investigation of microstructure and electrochemical hydrogen storage thermodynamic and kinetic properties of ball-milled CeMg12-type composite materials

Abstract

The ball milling method was used to prepare CeMg12/Ni composite hydrogen storage materials with nanocrystalline and amorphous structure in order to improve the electrochemical hydrogen storage and kinetic properties of alloy materials. The phase composition and crystalline structure were characterized by X-ray diffraction (XRD) and high resolution transmission electronic microscopy (HRTEM). The electrochemical discharging performances were measured though discharge capacity and cycling stability. High rate dischargeability (HRD), electrochemical impedance spectroscopy (EIS) and hydrogen diffusion behavior were utilized for studying the change of electrochemical kinetics. Results indicate that adding Ni significantly strengthens the glass forming ability of alloy samples in the process of ball milling. The maximum discharging capacity of the ball-milled composites monotonously goes upward from 46.7 to 1061.2 mAh/g with an increment in Ni content from 50 to 200 wt%. The increasing Ni content results in an obvious reduction in thermodynamic parameters (including enthalpy change ΔH and entropy change ΔS) of ball-milled composites. Besides, the addition of Ni speeds up the hydrogen diffusion rate inside the alloy. Meantime, the addition of Ni can also diminish the activation energy, which is helpful for ameliorating the electrochemical reaction kinetics on the surface of alloy. Keywords: Cycling stability, Thermodynamic stability, Charge transfer reaction, Hydrogen diffusion coefficient, Activation energy