The Power Conversion Efficiency of the Thionine Photoelectrochemical Cell Containing Uncoated and Thionine Coated Photoelectrodes

The power conversion efficiencies, voltage efficiencies, and current efficiencies of thionine cells containing various combinations of thionine coated and uncoated gold and electrodes have been determined. Cyclic voltammetry was used to determine coating thicknesses and to ascertain whether the thionine/leucothionine couple or the Fe 3+ /Fe 2+ couple was reversible on the various electrodes. The power conversion efficiency of the thionine cell containing two uncoated gold electrodes was , and contrary to previous predictions, when the photoelectrode was coated with thionine, the efficiency did not increase, but was reduced by a factor of 19. Larger decreases in efficiency were observed when photoelectrodes were coated with thionine. Previous electrochemical studies have suggested that the thionine coating suppresses the Fe 3+ /Fe 2+ couple and is reversible towards the thionine/leucothionine couple in solution, these being the requirements for optimal power output. This study has shown that both solution couples are substantially suppressed, the reported reversibility toward the thionine couple arising from facile oxidation and reduction of thionine in the dye coating, the latter producing negligible photoelectrochemical activity.