Electrochemical behavior of sol-gel produced Ni and Ni-Co oxide films

Ni and mixed Ni-Co oxide films were formed at Pt substrates by the sol-gel technique and studied electrochemically in 1 M NaOH solutions. All sol-gel films under study have to be found amorphous. The charge densities of these films are quite high compared to oxides formed by the anodic oxidation of metallic substrates. Mixed Ni-Co oxide films display higher charge densities, broader CV peaks, and negatively shifted equilibrium potentials vs. pure Ni oxide films. At slow sweep rates, all films studied showed kinetically reversible surface electrochemical behavior. At higher sweep rates, the redox reactions became kinetically irreversible, being either surface reactions with no diffusion limitations or controlled by the diffusion rate of species inside the film. The effect of the oxide film formation conditions, i.e., the withdrawal rate of the substrate from the sol solution and the firing temperature, on the electrochemical efficiency of the oxide films was also studied.