Hole annihilation vs. induced convection: Breakdown of different contributions to the photocorrosion mechanism of oxide-covered iron

Abstract

The mechanism behind corrosion rate increase of anodised iron under illumination has been studied by comparing photocurrents with corrosion currents from polarisation curves under controlled convection. Under illumination with photon energies larger than the iron oxide band gap of ~2 eV, corrosion current densities increased by maximum 30%, triggered largely by hole annihilation through cation dissolution. Thermal effects in the oxide also play a role. Photocurrent measurements indicate little upward band bending, with fluctuations, in the n-type oxide at open circuit. The contributions of different mechanisms to the photocorrosion rate have been quantified, relevant for steels and photoelectrochemical water splitting.