Anodic oxide films on stainless steel as prospective photo-anodes for light-assisted electrochemical water splitting

Anodic oxides are synthesized on austenitic stainless steel by different methods - galvanostatic, mixed, tensiodynamic + galvanostatic and potentiodynamic + potentiostatic, and stabilized by thermal treatment. Their thickness, elemental, and chemical composition are estimated using X-ray photoelectron spectroscopy and Glow discharge optical emission spectroscopy. Thin bilayer oxides are formed, the outer layer being close to pure Fe2O3 and the inner layer enriched in Cr and Mo. Electrochemical impedance spectroscopic and capacitance potential measurements indicate that the oxides are n-type semiconductors in which both shallow and deep donor states are present. Photoelectrochemical measurements indicate that the films absorb light in the whole visible part of the spectrum, and the kinetics of charge transfer and recombination are quantitatively characterized by intensity modulated photocurrent spectroscopy. The films are good photo-catalysts for hydrogen peroxide oxidation, the best performance being exhibited by galvanostatically and potentiodynamically + galvanostatically formed oxides.