Electrodeposition of PbO2+CoOx composites by simultaneous oxidation of Pb2+ and Co2+ and their use as anodes for O-2 evolution

PbO2 + CoOx composites have been deposited by anodisation of sulphamate sol utions containing Pb2+ and Co2+ ions. The effect of experimental variables, like total Co2+ + Pb2+ concentration, Co2+/(Co2+ + Pb2+) ratio, potential, pH and angular speed of the anode, on the deposit composition has been inv estigated. The results are discussed according to the theories developed fo r the cathodic deposition of alloys, concluding that the system conforms to the trends typical of irregular deposition. XRD and XPS analyses have show n that the deposits are amorphous, but have not allowed to fully elucidate the nature of the Co containing compound(s) codeposited with PbO2. When use d as anodes for oxygen evolution in aqueous NaOH, the PbO2 + CoOx composite s exhibit Tafel slopes of ca. 60 mV decade(-1) and a reaction order of 1 wi th respect to OH-. Their overpotential is similar to that of PbO2 + Co3O4 c omposites prepared by anodisation of suspensions. A marked activation of th e PbO3 + CoOx electrodes, during ca. 3 days of continuous oxygen evolution, is explained as the result of an increase of the Co surface concentration, as shown by XPS and impedance data. (C) 2000 Elsevier Science Ltd. All rig hts reserved.