The effects of surface treatment on metal hydride electrodes using a weak acid solution containing Ni(II)
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A novel surface treatment method using a weak acid solution containing Ni2+ ions (WANi) for AB(5)-type hydrogen storage alloys is introduced. The properties of treated and untreated metal-hydride (MH) electrodes were investigated using several electrochemical and spectroscopic methods. Ex-situ scanning tunnelling microscopy (STM) and electrochemical results showed that the WANi process modified the alloy surface layer under modest reaction conditions and enhanced the initial electrochemical performances of the electrodes. In-situ confocal microprobe Raman spectroscopic results demonstrated that the formation, growth and properties of alloy surface oxide layers exhibited some differences on the microscopic level. In addition, manganese and cobalt segregated and progressively enriched the alloy surface and were subsequently oxidized/reduced during charge-discharge processes. The changes in the composition and structure of the surface layer of the electrodes are believed to be an important factor causing the deterioration of MH electrodes. (C) 2001 Elsevier Science B.V. All rights reserved.