Comparative study on the structure and electrochemical hydriding properties of MgTi, Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys prepared by high energy ball milling

MgTi, Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys doped with 10 wt.% Pd were prepared by high energy ball milling and evaluated as hydrogen storage electrodes for Ni-MH batteries. X-ray diffraction analyses indicated that the Mg0.5Ni0.5Ti and MgTi0.5Ni0.5 alloys could be monophased or composed of a nanoscale mixture of MgTi + NiTi and MgTi + MgNi phases, respectively. Their hydrogen storage characteristics were investigated electrochemically in KOH electrolyte. No activation step was observed during the cycling of the Mg-Ti-Ni electrodes in contrast to that observed with the MgTi electrode. The highest hydrogen discharge capacity was obtained with the MgTi0.5Ni0.5 electrode (536 mAh g(-1)) compared to 401 and 475 mAh g(-1) for the Mg0.5Ni0.5Ti and MgTi electrodes, respectively. The ternary Mg-Ti-Ni alloys showed a better cycle life with an average capacity decay rate per cycle lower than 1.5% compared to similar to 7% for the binary MgTi electrode. The Mg-Ni-Ti electrodes also displayed a much higher discharge rate capability than the binary MgTi electrode, especially with the Mg0.5Ni0.5Ti electrode. The origin of this was established on the basis of the anodic polarization curves, where a substantial decrease of the concentration overpotential (reflecting a higher hydrogen diffusivity) was observed for the Mg0.5Ni0.5Ti electrode. (C) 2010 Elsevier B.V. All rights reserved.