Electrochemical reactions of mixed cobalt/nickel oxide hydroxides in alkaline electrolyte

Thin films of mixed cobalt/nickel oxyhydroxides were electrodeposited on platinum substrates. The electrochemical reactions of these materials were characterized as a function of composition and potential in alkaline electrolytes. The materials formed by electrochemical reaction were also characterized structurally from X-ray diffraction powder data. Evidence is presented for several types of materials that are formed as the cobalt levels are increased in the oxyhydroxide. These materials range from solid-solution beta-nickel oxyhydroxide phases when the cobalt content is less than about 10 percent, to several mixed nickel/cobalt phases formed at intermediate cobalt concentrations, and finally above 90 percent cobalt to the doped cobalt oxyhydroxides. Materials formed at intermediate cobalt levels adopt nickel-rich structures below 50 percent cobalt and cobalt-rich structures above 50 percent cobalt. The nickel-rich and the cobalt-rich materials posses the electrochemical activity of nickel oxyhydroxides, although the cobalt-rich structure appears to have a charge storage capacity reduced approximately by a factor of 2.