Effects of microencapsulation on the electrode behavior of Mg2Ni-based hydrogen storage alloy in alkaline solution

In order to improve the electrochemical performance of Mg2Ni-based hydride electrode in alkaline solution, the multicomponent Mg-2 Ni-based alloy (Mg1.9Y0.1Ni0.9Al0.1) powder was microencapsulated with Ni-P, Ni-Pd-P and NI-B coatings, respectively, using a low-temperature electroless plating method. The electrode characteristics were examined such as electrochemical capacity, high-rate dischargeability and cycle life, in comparison with those of the electrode fabricated from a bare (uncoated) alloy powder. It was found that the surface modifications with Ni alloy coatings effectively improved the electrode performance of Mg2Ni-based alloy. The Ni-Pd-P coated alloy electrode showed the highest discharge capacity and high-rate dischargeability, whilst the Ni-P coated alloy electrode displayed the slowest capacity decay. The electrochemical performance of the modified Mg2Ni-based alloy was characterized using d.c. polarization and a.c. impedance technique, and its phase composition and microstructure were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). It was found that the surface microencapsulation of alloy powder was effective in improving the electrode discharge performance, but seems to be ineffective in prohibiting disintegration of the Mg2Ni-based alloy powder. (C) 1998 Elsevier Science S.A.