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Abstract: Mechanical grinding (MG) leads to a sequential phase transition of γ-MnO2 to form the thermodynamically stable α-Mn2O3 and, subsequently, Mn3O4 depending on the duration of MG treatment. By MG treatment for 150h, α-Mn2O3 became a predominant species. A subsequent transition to Mn3O4 was observed on further MG treatment for 200h. The particle size of the resultant manganese oxides was reduced to as small as 20nm after 300h of MG treatment. The change in the specific capacitance of manganese oxides obtained was monitored by XRD and electrochemical experiments. It was observed that the specific capacitance of MG-treated manganese oxides depends on the amount of γ-MnO2 left without phase transition. [Copyright &y& Elsevier]

Atomization, crystallinity, and electrochemical characteristics of powdery RuO2 treated by mechanical grinding (MG) were examined. XRD analysis, N2 adsorption/desorption measurements, and TEM observations showed that MG generated isotropic and rapid atomization of RuO2 particles in the initial stage of treatment (up to 190 h). Further MG resulted in gentle atomization with anisotropy in a and c axial directions. Electrochemical measurements showed that the specific capacitance of treated RuO2 increased with increasing MG time. By the MG 400 h treatment, the specific capacitance was 132 F/g, which was about 80-times greater than that of the untreated sample. This increment was attributed to the increase in the specific surface area of RuO2 powder owing to the isotropic atomization caused by MG treatment. [Copyright &y& Elsevier]

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 change/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 ∼220 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. [Copyright &y& Elsevier]