Combining Bulk Charge Transport and Surface Charge Transfer to Design Titanium-Doped Hematite Homojunction Photoanodes

Ti doping can improve the photoelectrochemical water splitting performance of hematite. However, the effect of doping on regulating small polaron hopping in the bulk and charge transfer properties on the solid–liquid interface is not fully understood. In this paper, we investigate the effects of titanium doping on hematite by decoupling a hematite homojunction structure into bulk and surface layers. We found that 3% Ti doping remarkably reduces the small polaron hopping (SPH) barrier, which leads to the high bulk charge transport, and 5% Ti doping significantly passivates the recombination of the surface states (r-SS) of hematite and promotes the conversion of the surface holes to long-lived reaction intermediates (i-SS) on the solid–liquid interface, which leads to the high surface charge transfer. Based on the above results, we report first an unconventional Ti-doped hematite homojunction design that is established with 3% Ti-doped hematite as the underlayer and 5% Ti-doped hematite as the surface layer. The homojunction exhibits a significantly enhanced photocurrent density (1.27 mA cm–2) compared to that of the typical type-II hematite structure at 1.5 VRHE. This work has well demonstrated a new homojunction design strategy for enhancing the photoelectrochemical water splitting.