Activating titanium dopants in hematite photoanode by rapid thermal annealing for enhancing photoelectrochemical water oxidation

Doping with tetravalent titanium cation impurities is an effective means to enhance the performance of hematite (α-Fe 2 O 3 ) photoanodes. These nevertheless face problems of inefficient activation of impurity donors, which thereby impairs the photoelectrochemical water oxidation property of hematite. Herein, we propose a simple method to activate Ti 4+ dopants in spray-pyrolyzed hematite thin films via a rapid thermal annealing (RTA) treatment. The donor carrier density of Ti-doped Fe 2 O 3 thin films (doping level, i.e., Ti/Fe: 0.5–10%) is significantly increased by RTA at 700 °C for 30 s, for instance, ca. 1.35 × 10 19  cm −3  at the doping level of 5% (5%-Ti:Fe 2 O 3 -700). This is 19.3 times as high as those treated by traditional annealing in a muffle furnace at 500 °C for 1800 s (5%-Ti:Fe 2 O 3 -500). A photocurrent density of 5%-Ti:Fe 2 O 3 -700 for water oxidation reaches 0.91 mA cm −2 at 1.23 V vs. RHE. This is ca. 6-fold higher than 5%-Ti:Fe 2 O 3 -500. Electrochemical impedance spectroscopy , XRD, Raman spectroscopy, and scanning probe microscopy measurements suggest that RTA performs more efficiently than traditional annealing for promoting the substitutional incorporation of Ti 4+ cations into the hematite lattice. This simple RTA treatment for donor-activation should be applicable to other semiconductor-dopant combinations—thin films or nanostructures , for the development of high-performance photoanodes for water oxidation.