PROBE BEAM DEFLECTION INVESTIGATION OF THE CHARGE STORAGE REACTION IN ANODIC IRIDIUM AND TUNGSTEN-OXIDE FILMS

The electrochromic charge storage reaction in anodic iridium oxide films (AIROF) was investigated in aqueous electrolytes using the probe beam deflection (PBD) technique in combination with cyclic voltammetry. In acid electrolyte (1 M HClO4 for iridium and 1 M H2SO4 for tungsten) the sign of the PBD signal shows clearly that protons are ejected from the oxide film into the bulk electrolyte during oxidation. In basic electrolyte (1 M LiOH, 1 M NaOH) OH- ions are consumed during the oxidation reaction in the AIROF. The PBD signal for the main oxidation peak in the cyclic voltammogram was measured for iridium at different pHs. The change in sign of the beam deflection signal, indicative for one or the other reaction, occurs around pH 4 (+/- 0.5). The coloration of the AIROF in acid was monitored by means of photothermal deflection spectroscopy (PDS) and the results are in good agreement with published reflectivity data.