Sputtering of iridium-oxide films as protective layers for oxygen evolving photoanodes

An investigation of the Schottky barrier formation between iridium, iridium oxide films, and n-Si, n-GaAs substrates and its implications for oxygen evolution from water is presented. Iridium and iridium oxide films of 20-nm thickness were sputtered on single-crystalline n-Si and n-GaAs substrates. Schottky barrier heights reached values of 0.9 eV (Si) and 1.1 eV (GaAs) as determined by impedance measurements. Forward currents were usually not limited by the thermal emission model (n>or=2). EBIC data are presented in order to demonstrate the homogeneity of the surface coating. IrO₂-coated electrodes were investigated as photoanodes for oxygen evolution from aqueous electrolytes. The stability is better with silicon as substrate and comparable to literature data. Since IrO₂ does not dissolve electrochemically, but peels off only at impurities at the solid-state interface, stability is expected to improve under purer deposition conditions for the IrO₂ coating.