Photoelectrochemical performance of multi-layered BiO _x-TiO ₂/Ti electrodes for degradation of phenol and production of molecular hydrogen in water

Multi-layered BiO _x-TiO ₂ electrodes were used for the oxidation of chemical contaminants coupled with the production of H ₂ characterized by a synergistic enhancement. The BiO _x-TiO ₂ electrodes were composed of a mixed-metal oxide array involving an under layer of TaO _x-IrO _x, a middle layer of BiO _x-SnO ₂, and a top layer of BiO _x-TiO ₂ deposited in a series on both sides of Ti foil. Cyclic voltammograms showed that the BiO _x-TiO ₂ electrodes had an electrocatalytic activity for oxidation of phenol that was enhanced by 70% under illumination with AM 1.5 light. When the BiO _x-TiO ₂ anode was coupled with a stainless steel cathode in a Na ₂SO ₄ electrolyte with phenol and irradiated with UV light at an applied DC voltage, the anodic phenol oxidation rate and the cathodic H ₂ production rates were enhanced by factors of four and three, respectively, as compared to the sum of each light irradiation and direct DC electrolysis. These synergistic effects depend on the specific electrode composition and decrease on TaO _x-IrO _x and BiO _x-SnO ₂ anodes in the absence of a top layer of BiO _x-TiO ₂. These results indicate that the BiO _x-TiO ₂ layer functions as the key photo-electrocatalyst. The heavy doping level of Bi (25mol%) in TiO ₂ increases the electric conductivity of the parent TiO ₂.