Design of Ti-Pt Co-doped α-FeO photoanodes for enhanced performance of photoelectrochemical water splitting.

This study demonstrates Ti and Pt co-doping can synergistically improve the PEC performance of the α-FeO photoanode. By varying the doping methods, the sample with in-situ Ti ex-situ Pt doping (Ti-Pt) exhibits the best performance. It demonstrates that Ti doping in bulk facilities charge separation and Pt doping on the surface further accelerates charge transfer. In contrast, Ti doping on the surface inhibits charge separation, and Pt doping in bulk hinders charge separation and transfer. HCl treatment is used to minimize the onset potential further, while it is favorable for the ex-situ doped α-FeO, which is more efficient on Ti than the Pt-doped ones. On the ex-situ Ti-doped α-FeO after HCl treatment, anatase TiO is probed, suggesting that Ti-O bonds accumulate when Fe-O bonds are partly removed, which enhances the charge transfer in surface states. Unfortunately, HCl treatment also induces lattice defects that are adverse to charge transport, inhibiting the performance of in-situ doped α-FeO and excessively treated ex-situ doped ones. Coupled with methanol solvothermal treatment and NiOOH/FeOOH cocatalysts loading, the optimized Ti-Pt/FeO photoanode exhibits an impressive photocurrent density of 2.81 mA cm at 1.23 V vs. RHE and a low onset potential of 0.60 V vs. RHE.