Gradient Ti-doping in hematite photoanodes for enhanced photoelectrochemical performance

Hematite based photoanode is promising for solar water splitting while suffers from poor charge transport and separation efficiency that limit its practical application. Herein, we demonstrate two types gradient Ti-doped Fe2O3 photoanodes (Fe2O3 -Ti (TiO2 deposited on the top of Fe2O3) and Ti-Fe2O3 (Fe2O3 on the top of TiO2)) to enhance charge transport and separation efficiency. Interestingly, Fe2O3-Ti and Ti-Fe2O3 photoanodes exhibit almost identical PEC performance with photocurrent of 1.50 mA cm(-2) at 1.23 V vs. the reversible hydrogen electrode (RHE). However, the onset potential of Ti-Fe2O3 photoanode displays a cathodic shift of 80 mV comparing with that of Fe2O3-Ti photoanode. Moreover, the charge separation efficiencies on the surface (eta(surface)) for Fe2O3=-Ti and Ti-Fe2O3 can reach up to 96% at the higher potential range from 1.30 to 1.50 V vs. RHE, which are among the top values in the record of hematite-based photoanodes without co-cocatalyst. Further investigation demonstrates the forming of gradient Ti doping is not dependent on the location of the TiO2 layer, but mainly affected by the high annealing temperature. The enlarged contact area between hematite photoanode and the electrolyte, the improved charge separation efficiency, and increased charge carrier density are responsible for the enhanced PEC water splitting.