An in situ fluorine and ex situ titanium two-step co-doping strategy for efficient solar water splitting by hematite photoanodes

A unique two-step co-doping strategy of in situ fluorine doping followed by ex situ titanium doping enhances the performance of the hematite photoanode in photoelectrochemical water splitting much more effectively than single-step co-doping strategies that are either all in situ or all ex situ. The optimized fluorine, titanium co-doped Fe2O3 photoanode without any cocatalyst achieves 1.61 mA cm(-2) at 1.23 V-RHE under 100 mW cm(-2) solar irradiation, which is similar to 2 and 3 times those of titanium or fluorine singly-doped Fe2O3 photoanodes, respectively. The promotional effect is attributed to the synergy of the two dopants, in which the doped fluorine anion substitutes oxygen of Fe2O3 to increase the positive charges of iron sites, while the doped titanium cation substitutes iron to increase free electrons. Moreover, excess titanium on the surface suppresses the drain of in situ doped fluorine and agglomeration of hematite during the high-temperature annealing process, and passivates the surface trap states to further promote the synergy effects of the two dopants.

Automated summary

A two-step co-doping strategy using in situ fluorine doping followed by ex situ titanium doping significantly improves the performance of hematite photoanodes in photoelectrochemical water splitting. The optimized co-doped Fe2O3 photoanode achieves a current density of 1.61 mA cm(-2) at 1.23 V-RHE under solar irradiation, which is 2 and 3 times higher than that of singly-doped titanium or fluorine Fe2O3 photoanodes, respectively. The enhanced performance is attributed to the synergy of fluorine and titanium dopants, which increase positive charges and free electrons in the hematite structure.