Enhancement of photoelectrochemical hydrogen production from hematite thin films by the introduction of Ti and Si

Doped and undoped hematite (alpha-Fe2O3) thin film electrodes for photoelectrochemical hydrogen production have been prepared using reactive magnetron sputtering. We present an extensive characterization of the photoelectrochemical, structural, electrical, and optical properties of the alpha-Fe2O3 films to assess the mechanisms by which the dopants influence photoelectrode performance. The Si-doped and Ti-doped alpha-Fe2O3 exhibited much higher photoelectrochemical activity than the undoped material. The Ti-doped alpha-Fe2O3 showed. the largest photocurrent as well as the lowest onset potential, the highest electrical conductivity, the lowest activation energy, and the highest charge carrier density. The crystallographic orientation of the films does not appear to be a dominant factor affecting the photocurrent. The changes in conductivity with doping are insufficient to explain the observed changes in the photoelectrochemical activity. The proposed mechanism for the enhanced photocurrent is reduction of recombination due to an improvement of the charge-transfer rate coefficient at the surface and also possibly passivation of the grain boundaries by the dopants. A highly disordered surface and higher grain boundary recombination due to small crystals may explain the lower photocurrent of the Si-doped alpha-Fe2O3 compared to the Ti-doped material.