Effect of graphite (GR) content on electrochemical hydrogen storage performances of nanocrystalline and amorphous La9Ce1Mg80Ni5-Ni-GR composites synthesized by mechanical milling

The MgeNi-based alloy La9Ce1Mg80Ni5 was fabricated by a vacuum induction furnace with high purity helium gas. The surface modification of the as-cast alloys was operated by mechanical coating Ni and graphite (GR). The composites La9Ce1Mg80Ni5-200 wt% Ni-x wt.% GR (x = 0-4) with nanocrystalline and amorphous structures were synthesized by mechanical milling. Adding appropriate GR brings on the enhancement of ball-milling efficiency and inhibits the agglomeration of alloy powders. Furthermore, the discharge capacity of the composites obtains the maximal values with an optimized GR percentage. Increasing GR content from 0 to 4, the capacity retention rate at 20th cycle (S-20 = C-20/C-max) of the 20 h milled composite improves from 72.2% to 74.3% and that of the 80 h milled specimen changes from 54.4% to 56.9%. Electrochemical tests indicate that with the optimization of GR percentage, the composites can get the best electrochemical kinetic property, such as the highest HRD value, the highest hydrogen diffusion coefficient and the lowest charge transfer resistance. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.