Electrochemical hydrogenation of Ti45Zr38Ni17 quasi crystal and amorphous powders produced by mechanical alloying

The electrochemical properties of Ti45 Zr38 Ni17 amorphous and icosahedral (i) quasi-crystal electrodes synthesized by mechanical alloying and subsequent annealing were measured in a three-electrode cell at temperatures of 298 and 328 K. During electrochemical hydrogenation, the maximum H/M (number of hydrogen atoms per metal atom) value for the i-phase electrode reached 1.4, which corresponds to a theoretical capacity of 570 mAh/g. The discharge capacities for both the amorphous and i-phase electrodes at 298 K increased with increasing charge/discharge cycles at the initial stage because of an activation process. The maximum discharge capacity for i-phase and amorphous electrodes at 298 K were 23.9 and 5.9 mAh/g, respectively, at a current density of 15 mA/g. The maximum discharge capacity for the i-phase electrode, however, reached about 88 mAh/g after the first cycle at 328 K and then decreased as the number of cycles increased. The structure of the i phase was stable even after the discharge process of the 25th cycle, but the amorphous electrode converted to (Ti,Zr) H2 face-centered-cubic-type hydride, which substantially lowered its total discharge performance.