Influences of heat treatment on electrochemical characteristics of La_0.75Mg_0.25Ni_2.8Co_0.5 hydrogen storage electrode alloy

The influences of annealing treatment on the electrochemical and structural properties of La_0.75Mg_0.25Ni_2.8Co_0.5 hydrogen storage electrode alloy hydrogen storage alloy were investigated by means of electrochemical studies and X-ray diffraction(XRD) analyses. The XRD results reveal that the peak width gets narrower with increasing annealing temperature, which can be ascribed to the structural change and more homogeneous composition after annealing. Electrochemical studies show that the discharge capacity and the cycle stability of the alloy electrodes increase after annealing. The maximum discharge capacity, exchange current density J_O and limiting current density J_L of the as-cast alloy are 388 mA·h/g, 340.5 mA/g and 3068 mA/g, respectively, and they increased to 400 mA·h/g, 372.1 mA/g and 3399 mA/g for the alloy annealed at 1123 K for 8 h, respectively. Meanwhile, as the discharge current density is 1250 mA/g, the high rate dischargeability(HRD) increases from 77.4% for the as-cast alloy to 83.3% for the alloy annealed at 1123 K.