Electrochemical investigations on cobalt-microencapsulated MmNi2.38Al0.82Co0.66Si0.77Fe0.13Mn0.24 hydrogen storage alloys for Ni–MH batteries

Cobalt coatings were applied over lanthanum process-rich MmNi2.38Al0.82Co0.66Si0.77Fe0.13Mn0.24 alloy particles by an autocatalytic electroless deposition process. Electrode characteristics such as electrochemical capacity and cycle life were studied for the uncoated and coated alloys. The structure and morphology of the surface modified samples were characterized with XRD and SEM/EDAX techniques. The cobalt coating forms a thin layer on the surface of the core material and the coated alloys exhibit a 15% improvement in performance over the bare alloy. A comparison of the electrochemical impedance behaviour of the bare and cobalt-coated metal hydride electrodes at different states-of-charge reveals that the relaxation period is distinct for different SOCs. The cobalt microencapsulations influence the apparent activation energy of the dehydriding process. The calculated equivalent rate constant (keq) values confirm the improvement in reversibility for the cobalt-coated alloy as compared to the bare alloy.