Solar hydrogen is a sustainable energy carrier that can be produced from sunlight and water via photoelectrochemical “water splitting”. Hematite (alpha-Fe₂O₃) has an indirect band-gap (~2.2 eV) which allows the utilisation of a significant fraction of the solar spectrum. However, the water splitting efficiency of alpha-Fe₂O₃ is low, due to poor absorption characteristics, and large recombination losses in the bulk and at the surface. Nanostructuring has the potential to overcome some of the limitations of hematite, by increasing the effective photon path length in the photoactive material and reducing the distance that charge carriers need to travel in the low mobility material.

Doped (Si and Ti) and undoped alpha-Fe₂O₃ thin films have been prepared using vacuum deposition techniques. Extensive characterisation of the photoelectrochemical, structural, electrical and optical properties of alpha-Fe₂O₃ films was undertaken to study the effects of the dopants. Doped hematite exhibited much higher photoelectrochemical activity than the undoped material, 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.

Photoelectrodes have been fabricated by coating nanostructured substrates with doped alpha-Fe₂O₃ thin films. Composite nanostructured electrodes showed lower quantum efficiencies than equivalent thin films of hematite, though relative enhancement of collection of long wavelength charge carriers was observed, indicating that nanostructured composite electrodes are worthy of further investigation.