Hematite is the prototypical semiconducting material used as a SWS photoanode. It is characterized by a band gap of 2.15 eV, which perfectly matches the solar spectrum for optimized absorption, which is ideal for direct SWS . Compared to materials exhibiting higher photocurrents (e.g. BiVO4) , pristine hematite is less efficient for SWS mainly because of the reduced hole mean free path (~ 2-4 nm) and poor surface kinetics, mainly due to a complex oxygen evolution reaction (OER) mechanism . Therefore, the photocurrents obtained using pristine hematite as photoanode are much lower (in µA range) than the expected value of 12.6 mA/cm 2 , calculated assuming 100% collection and conversion of the photogenerated electron-hole pairs to electronic current .