Progress and problems in visible light water splitting

Visible light water splitting in dye sensitized solar cells has now been reported by several groups who have used transition metal oxides or dyes coupled to catalyst clusters as photosensitizers. In these cells and in semiconductor-based photoelectrochemical cells, there are system-level issues that must be considered in the context of water electrolysis. These include the need for membranes that conduct protons at the pH where the electrocatalysts operate and where the other components of the system are stable, as well as the problem of fuel crossover and catalytic oxidation. We will report the effects of some of these parameters in membrane-based cells containing phosphate and borate electrolytes. In the water-splitting dye cell, the quantum efficiency is sensitive to the presence of buffers because protons generated at the photoanode lower the driving force for water oxidation and thus complicate the electron transfer kinetics. New strategies for controlling the relative rates of forward and back electron transfer in these cells will be described.