Photoelectrochemical performance of multi-layered BiO_x–TiO_2/Ti electrodes for degradation of phenol and production of molecular hydrogen in water

Abstract

Multi-layered BiO_x–TiO_2electrodes 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 (25 mol%) in TiO_2 increases the electric conductivity of the parent TiO_2.

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