Enhanced photoelectrochemical water splitting performance of hematite photoanodes via uniform Ti and gradient Ge co-doping

The photoelectrochemical (PEC) water oxidation reaction on hematite (α-Fe2O3) photoanodes has certain limitations, especially poor conductivity and rapid carrier recombination. To address the above issues, uniform Ti doping and gradient Ge doping were used to construct Ti-Ge co-doping hematite (Ti-Ge:Fe2O3). A series of characterization tests showed that uniform Ti doping increased the carrier concentration and conductivity, while gradient Ge doping improved the charge separation efficiency. Meanwhile, Ti-Ge co-doping hematite constructed a gradient energy band structure, which played a contributing role in improving the charge separation efficiency. The co-doping of other metal elements with Ti was carried out, all of which showed significant effects in improving the PEC performance. This suggested that the Ti:M (M=metal elements) co-doping hematite in improving PEC performance was universal. In addition, when the NiFeOOH co-catalyst was loaded on Ti-Ge:Fe2O3, the onset potential shifted negatively 150 mV and photocurrent density significantly improved, which was about 9.7 times higher than that of bare Fe2O3. This work provides a novel strategy of improvement of PEC performance on hematite by co-doping engineering.