Detection of oxygen evolution from nickel hydroxide electrodes using scanning electrochemical microscopy

An important parameter for judging the performance of the nickel hydroxide electrode in electrochemical energy storage devices is the difference between the oxygen evolution potential and the nickel hydroxide oxidation potential. Scanning electrochemical microscopy (SECM) has been investigated as an accurate method for the determination of the potential at which nickel hydroxide formulations evolve oxygen. Oxygen evolution from a variety of nickel hydroxide substrate electrodes in KOH was studied in situ by SECM. The SECM probe tip, positioned just above the substrate surface, was used to detect the oxygen evolved while cyclic voltammetry was also performed on the substrate, thus separating the detection of oxygen evolution from the nickel hydroxide oxidation process. A range of supporting substrates were investigated: conducting glass (indium tin oxide), glassy carbon, and nickel metal, with either nickel hydroxide formulations pasted or microparticles abrasively attached onto the support. Graphite, as a conductive additive to Ni(OH)(2) paste formulations, gave more positive oxygen-evolution overpotentials than similar formulations containing filamentous nickel as the conductive additive. Unmilled nickel hydroxide samples outperformed milled samples; higher rates of oxygen evolution and lower capacities were obtained from the milled nickel hydroxide samples as determined by SECM and high-rate charge/discharge cycling measurements. (C) 2008 The Electrochemical Society.