Overcoming Acidic Challenges in Hematite Photoanodes: Charge Transport Engineering and Catalytic Interface Optimization.

Hematite (α-FeO) has emerged as a promising photoanode material for photoelectrochemical (PEC) water splitting in acidic environments, owing to its abundance, non-toxicity, and favorable bandgap (≈2.1 eV) enabling visible-light absorption. Despite its high theoretical photocurrent density and stability, practical applications are hindered by rapid charge recombination, low hole mobility, and poor oxygen evolution reaction (OER) kinetics under acidic conditions. This review highlights recent advances in optimizing hematite-based photoanodes through nanostructuring, doping, heterojunction engineering, and surface modifications. In particular, heterojunction architectures promote efficient interfacial charge transfer, and surface modifications mitigate oxygen evolution overpotentials and enhance corrosion resistance in acidic media. These strategies collectively boost photocurrent densities and operational stability. Challenges remain in achieving balanced light absorption, carrier dynamics, and acid-resistant interfaces. Future directions emphasize atomic-level catalyst design, tandem configurations, and mechanistic studies to bridge the gap between theoretical potential and scalable PEC systems. This work underscores hematite's viability for solar-driven acidic water splitting, offering insights for next-generation photoanode development.