Electrochemical studies of the effect of surface modification of amorphous MgNi electrodes by carbon or Ni

The effect of surface modification of amorphous MgNi by carbon or Ni was examined by conventional charge/discharge cycle tests and by a newly developed micro-paste electrode method. The charge/discharge tests showed that the surface modification by Ni had no effect on the capacity degradation of amorphous MgNi. The carbon modification, however, clearly improved the degradation; the discharge capacity after six cycles was still similar to220 mA/g, which was about twice that of the unmodified sample. In cyclic voltammograms (CVs) obtained for the carbon-modified samples using the micro-paste electrode technique, the potential at the rising of the cathodic current shifted to the anodic direction and the anodic peak was sharper and larger than those for the unmodified sample. In addition, the CVS observed for carbon-modified samples immersed in 6 N KOH solution, which can be regarded as degraded samples, revealed that the deposited carbon suppressed the reduction in the electron transfer rate due to Mg(OH)(2) formation. Potential step measurements for the carbon-modified samples, on the other hand, showed that carbon modification on MgNi did not affect the diffusion process of hydrogen. (C) 2002 Elsevier Science B.V. All rights reserved.