Hematite Photoanode for Efficient Photoelectrochemical Water Splitting: Recent advances and outlook

Due to high abundance, non-toxicity, and moderate bandgap, Hematite (α-Fe₂O₃) photoanodes have always been a research hotspot in photoelectrochemical (PEC) water splitting. However, the 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 reaction on the surface, enhancing charge separation and transport in the bulk, and paralleling multi-stacked photoelectrodes. The surface reaction kinetics of hematite photoanodes could be improved by 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 heterojunction/homojunction constructing. In particular, an innovative parallel multi-stacked hematite photoanodes has made a significant breakthrough 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. Besides, the typical methods of enhancing light absorption and accelerating charge transport are discussed, especially for element doping and hetero-/homojunction.