The detailed phase transformation in the charge-discharge process for the nickel hydroxide electrode have been examined by using the high-energy synchrotron X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD). The structural refinement for the β-Ni(OH)2 and the β-NiOOH have been done successfully on the basis of two phase models of the ideal and fault phases. At 0% of SOC, it was found that the sample consisted of 80% of the ideal β-Ni(OH)2 phases and 20% of the fault ones. At 100% of SOC, the ideal and fault β-Ni(OH)2 phases were transformed to the ideal and fault β-NiOOH phases, respectively. It was found that the fault phases contained a larger amount of intercalated potassium ions and H2O (OH−) than the ideal ones. At 150% of SOC, the only ideal β-NiOOH phases was transformed to the ideal γ-NiOOH phases, accompanied by further intercalation of the potassium ions and H2O (OH−) into the interlayer
In order to improve cathode property of LiMn2O4, we performed supersonic-wave treatments on LiMn2O4 powder in a Zn-containing aqueous solution and then heat-treated the obtained powder. Investigations on the samples clarified that the lattice constant of LiMn2O4 decreased and the Mn valence increased by the treatments, indicating a partial substitution of Zn for Mn. From charge-discharge cycle tests, it was demonstrated that the cycle performance of LiMn2O4 was drastically improved by the treatments although the first discharge capacity was deteriorated. We also carried out the investigations on the cathodes and electrolytes after the cycle tests, and found that the crystal structure of LiMn2O4 was stabilized by the treatments. From these results, it could be concluded that the partial substitution of Zn for Mn and/or a surface modification induced by the supersonic-wave treatments stabilized the crystal structure of LiMn2O4 and thus resulted in the better cycle performance.
Platinum-ruthenium catalysts of various Pt:Ru ratios were prepared by a newly developed three-step method for use as anodes in stationary polymer electrolyte fuel cells. As the first step, a well-dispersed platinum catalyst was prepared, and then ruthenium was deposited in the vicinity of the platinum particles by a chemical deposition method as the second step. As the final step, the Pt–Ru catalysts were heat-treated to obtain well-alloyed structures. The Pt–Ru catalysts prepared by this method showed good CO tolerance, even though the particle size was relatively large. The CO tolerance increased with increasing the ruthenium content, and the highest CO tolerance was obtained at Pt:Ru ratios in the range of 1:2 to 1:3. On air bleeding, the catalysts of a wider range of Pt:Ru ratios showed good CO tolerance. Potential sweep durability tests revealed that the stability of the Pt–Ru catalysts of Pt:Ru=1:1 against high potentials (1000 mV vs. RHE) was lower than that of the catalysts of Pt:Ru=1:1.5 and 1:2.
Electrochemical deposition of Ni/SiC was carried out under centrifugal fields (69 and 113 G) and Earth’s gravity (1 G). The volume fraction of SiC in a nickel matrix was found to be increased by the applied gravitational force. In addition, morphological structure of the film was also affected by the centrifugal field. A plausible mechanism for the electrochemical deposition of Ni/SiC under the centrifugal force has also been proposed.