In situ XANES studies of electrodeposited nickel oxide films with metal additives for the electro-oxidation of ethanol

Electrodeposited nickel oxide electrodes with additives such as sodium, cobalt, ruthenium, and their combination were evaluated as the anode materials for the electro-oxidation of ethanol using in situ x-ray absorption near edge structure (XANES). Electrochemical properties of the electrodes were studied by monitoring oxidation states of metal oxides during oxidation of electrodes themselves, as well as during oxidation of ethanol, in alkaline media. The Ni-Co-Ru electrode showed the best performance with increased anodic peak currents and lower overvoltages for electrochemical oxidation of ethanol. Analysis of the XANES data for the Ni and Co K-edges of these composite electrodes revealed that both Ni and Co are in the Ni3+-Ni4+ and Co3+-Co4+ mixed states, respectively, depending on applied potentials. The presence of cobalt and/or ruthenium in nickel oxide films enhanced the electrode performances for ethanol oxidation due to generation of highly oxidized states of cobalt and ruthenium via electrogenerated nickel oxides. (C) 2003 The Electrochemical Society.