Synergistic Surface/Bulk Charge Modulation Enables Record-Level Photocurrent in Hematite Photoanodes without Co-Catalysts for Photoelectrochemical Water Splitting

Abstract Hematite (α-Fe2O3) photoanodes are limited by poor bulk conductivity and severe surface recombination, which hinder their photoelectrochemical (PEC) water-splitting activity. We demonstrate that a simple, rapid microwave-sintering (RMS) route simultaneously incorporates Ti into the bulk and establishes a Ge surface gradient in RMS@GeTi:Fe2O3 electrodes. This dual doping approach delivers a record photocurrent of 5.31 mA cm–2 at 1.23 V vs RHE under standard AM 1.5 G illumination, which is 11.3 times higher than pristine hematite (0.47 mA cm–2) and the highest value reported to date for bare α-Fe2O3 without co-catalysts. Systematic spectroscopic and electrochemical analyses disentangle the individual and synergistic roles of the dopants: Ti incorporation significantly enhances bulk carrier density, reduces the bulk resistance, and accelerates the transport of photogenerated carriers within the hematite lattice. Concurrently, it regulates the distribution of surface states, facilitating interfacial charge transfer. Meanwhile, the graded Ge dopant profile localized near the surface cooperatively modulates the hematite surface states and suppresses surface charge recombination. The combined Ge-Ti dual-doping strategy thus optimizes both bulk transport and surface water-oxidation kinetics, providing a scalable pathway toward high-performance hematite photoanodes without external catalysts or overlayers.