Microstructure and Electrochemical Performance of CeMg12/Ni/TiF3 Composites for Hydrogen Storage

Abstract

Ball milling was used to prepare CeMg12/Ni/TiF3 composite alloys in this study. Microstructures of experimental alloys were analyzed by scanning electron microcopy (SEM), x-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) with electron diffraction (ED). The electrochemical and kinetic characteristics of the ball-milled composite alloys were further evaluated based on their galvanostatic charge–discharge measurement, high-rate dischargeability (HRD), hydrogen diffusion behavior, as well as electrochemical impedance spectrum (EIS). Results indicated that the ball-milled alloy with 3 wt.% TiF3 exhibited the best electrochemical discharge capacity, which was not only related to the formation of amorphous and/or nanocrystalline phase but to the formation of MgF2 because it can effectively reduce the thermodynamic stability of hydride. With increasing TiF3, the cycle degradation rates of the milled alloys were ameliorated remarkably. This improvement was attributed to the formation of an amorphous phase (which possesses strong anticorrosive and antioxidation abilities) as well as the formation of MgF2 and TiNi secondary phases. The ball-milled alloy with 3 wt.% TiF3 additive exhibited the strongest electrochemical kinetic properties, related to the highest hydrogen diffusion rate in the alloy (which was associated with multiple defects and grain boundary of amorphous and/or nanocrystalline phases) and the electrochemical reaction on the surface of alloy (which was related to the lowest apparent activation energy).