Photoelectrochemistry of oxalate on particulate TiO2 electrodes

TiO2 electrodes were prepared by the electrophoretic immobilisation of Degussa P25 TiO2 powder on titanium alloy (Ti-6Al-4V). These electrodes were used as photoanodes in a two compartment photoelectrochemical cell to investigate the photocatalytic oxidation of oxalate. The effects of electron accepters, i.e. oxygen and Fe3+, on the rate of mineralisation of oxalate were determined. Significant increases in the short-circuit photocurrent densities were observed upon the addition of oxalate to the anode compartment when oxygen was present only in the cathode compartment. When oxygen was present in both the anode and cathode compartments, little photocurrent was observed. Oxygen scavenges both conduction band electrons from the TiO2 surface and primary radicals formed in the initial one electron oxidation of oxalate. An increase in the anodic photocurrent and rate of degradation of oxalate was observed when oxygen was replaced with Fe3+ as the electron acceptor in the cathode compartment. The TiO2 coated anodes behaved as microporous nanocrystalline film electrodes where the anodic photocurrent is dependent on the diffusion of majority charge carriers through the film. Oxalate acts as an efficient hole acceptor, inhibiting the photoanodic production of oxygen. (C) 1998 Elsevier Science S.A. All rights reserved.