An intensity modulated photocurrent spectroscopy study of the role of titanium in thick hematite photoanodes

In this Letter, the role of Ti addition in thick hematite mesoporous photoanodes was elucidated by performing intensity modulated photocurrent spectroscopy (IMPS) monitoring its charge carrier dynamics during water oxidation. Interface engineering associated with doping of hematite is crucial to develop highly efficient thick photoanodes. Photoelectrochemical data recorded under front- and back-side illumination show that Ti insertion mitigates the collection deficit faced by hematite due to an energy barrier decrease between the grains and a change in the surface chemistry. IMPS reveals that Ti clearly influences the hematite film performance by increasing the charge separation efficiency due to its segregation at the hematite interface. However, Ti insertion does not enhance the kinetics of water oxidation at the solid-liquid interface. These facts indicate that Ti mainly affects the hematite electronic properties instead of accelerating the surface processes. This comprehensive understanding of the electronic transport and charge carrier dynamics in Ti:hematite photoanodes enables the control and design of better interfaces for more efficient photoelectrochemical water splitting.