Photo-chargeable and dischargeable TiO2 and WO3 heterojunction electrodes

TiO2 and WO3 heterojunction electrodes are studied for their bi-functionality on harvesting light and storing energy. Both semiconductors are fabricated either 'single' (mixed) electrodes or two different electrodes galvanically coupled in a mixed electrolyte of 0.1 M sodium formate and 0.1 M sodium chloride. Irradiation of AM 1.5-light shifts the open circuit potentials (OCPs) of the mixed and coupled electrodes from around -0.1 V-SCE (dark OCPs) to a potential range between -0.8 and -0.5 V-SCE, which slowly return to their respective dark OCPs over a period of around 14 h. Such discharging periods are significantly influenced by the irradiation (photocharging) time and weight or area ratios of TiO2 and WO3. When the TiO2 and WO3 mixed electrodes are galvanically coupled to stainless steel electrodes for application to anticorrosion, the mixed potentials of the couple are maintained at ca. -0.4 V-SCE over 10 h even after light off. The measured galvanic currents verify that the photogenerated electrons of TiO2 flow to WO3 (charging) and even overflow to the steel (cathodic protection) during the irradiation, while the stored electrons at WO3 flow to the galvanically coupled steel electrodes directly or through the TiO2 upon light off. (C) 2011 Elsevier B.V. All rights reserved.