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Analysis of Hydration Number in Cobalt Oxyhydroxide Films Using the Quartz Crystal Microbalance

Y. Matsumoto, N. Bando, J. Hombo, and T. Sasaki
[Journal of Electroanalytical Chemistry, Vol. 395, pp. 45-49, 1995]

The hydration numbers n of the deposited cobalt oxyhydroxide (CoOOH„nH2O) films were measured using an in-situ quartz crystal microbalance, and the effect of the La3+ ion on the hydration was studied. The hydration number of the deposited film was very high during the initial stage of the electrolysis (n „ 10), but decreased to a constant value. The constant values of the hydration number were about 3 and 1 for CoOOH„nH2O films deposited in Co(CH3COO)2 and in other solutions (Co(NO3)2, CoCl2, CoSO4) respectively. The anion effect of CH3COO- on hydration was discussed. The incorporation of an La3+ ion increased the hydration number by about 5. Consequently, CoOOH„nH2O„La3+„5H2O was proposed for the composition of the deposited cobalt oxyhydroxide film containing La3+ (atomic ratio La/Co = 1). The combination state of La3+ in this composition was also discussed.

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