Rutile TiO₂ as an Anode Material for Water-Splitting Dye-Sensitized Photoelectrochemical Cells

Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) use a wide bandgap metal oxide semiconductor functionalized with a light-absorbing dye and water-oxidation catalyst to harvest light and drive water oxidation, respectively. We demonstrate here that the rutile polymorph of TiO₂ (r-TiO₂) is a promising anode material for WS-DSPECs. Recombination between the injected electron and oxidized sensitizer with r-TiO₂ is an order of magnitude slower than with anatase TiO₂ (a-TiO₂), with injection yields approaching 100%. Studies with a reductive quencher demonstrate that r-TiO₂ is significantly more efficient than a-TiO₂, while exhibiting greater dye stability. Furthermore, comparison of direct band gap excitation photocurrent generation for bare and sensitized r-TiO₂ suggests that the sensitizer functions as a light harvester and redox mediator.