Hematite photoanode for efficient photoelectrochemical water splitting: recent advances and outlook

Due to their high abundance, non-toxicity, and moderate bandgap, hematite (α-Fe₂O₃) photoanodes are a research hotspot in photoelectrochemical (PEC) water splitting. However, their performance is severely limited by low carrier mobility, short hole diffusion length, and slow oxygen evolution reaction kinetics. In this review, we discuss recent advancements of hematite photoanodes by promoting water oxidation reactions on the surface, enhancing charge separation and transport in the bulk, and parallel multi-stacked photoelectrodes. The surface reaction kinetics of hematite photoanodes could be improved by a surface hole storage layer, surface-loaded cocatalyst, and surface post-treatment. The charge separation and transport in the bulk could be enhanced by dual element doping and hetero-/homojunction construction. In particular, innovative parallel multi-stacked hematite photoanodes have made a significant breakthrough in terms of photocurrent density, achieving the approximate theoretical value of 10 mA cm⁻² at 1.23 V_RHE under 100 mW cm⁻² solar irradiation. Furthermore, typical methods of enhancing light absorption and accelerating charge transport are discussed, especially for element doping and hetero-/homojunction.