Hematite has emerged as a good photocatalyst for efficient solar water splitting due to its favorable optical band gap (2.1–2.2 eV), extraordinary chemical stability in oxidative environment, abundance, and low cost. According to theoretical prediction, the solar-to-hydrogen efficiency of hematite can be 16.8% and the water splitting photocurrent can be 12.6 mA cm^-2. However, the practical performance of hematite for solar water splitting is far from the ideal case which has been limited by several factors such as poor conductivity, short lifetime of the excited-state carrier (10^-12s), poor oxygen evolution reaction (OER) kinetics, short hole diffusion length (2–4 nm), and improper band position for unassisted water splitting. In our recent work, enormous efforts have been focused on improving the performance of hematite nanostructure photoelectrode. Different methods such as morphology control, elemental doping, and improvement of the charge transport of hematite have been developed to improve the performance of hematite photoelectrode in solar water splitting. We present the preparation of Ti-doped and H₂-treated hematite nanostructures. The H₂-treated hematite photoelectrode showed a high photocurrent of 2.28 mA/cm² at 1.23 V vs. RHE, which was over 2.5 times than that for pristine hematite. Moreover, when compared to hematite photoelectrode with oxygen vacancies but treated by controlling the oxygen content in the sintering process, a cathodic shift of the onset potential was observed by about 120 mV (from 0.99 to 0.87 V vs. RHE). The cathodic shift of the onset potential was attributed to the surface effect of H₂-treatment. The Ti-doped hematite nanostructures with optimized oxygen vacancies achieved a remarkable maximum photocurrent value of of 4.56 mA/cm²at 1.6 V vs. RHE. Moreover, Ti-doping can expand the applicative partial oxygen pressure to a wide range compared to that for undoped hematite. The expansion of partial oxygen pressure range might be useful for the practical application. The coupling of extrinsic Ti-doping and intrinsic oxygen vacancies stands for an effective strategy to design oxide-based photoanodes for efficient solar water oxidation. 

Reference: 

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