Shallow Zirconia Diffusion Synergistically Enhances Surface Charge Transport in Ge‐Doped Hematite for Efficient Photoelectrochemical Water Splitting

Iron oxide‐based materials suffer from inherently low conductivity and severe charge carrier recombination, resulting in poor PEC performance and low solar‐to‐hydrogen (STH) conversion efficiency. In this study, we aim to enhance the intrinsic conductivity of pristine hematite through a dual co‐doping strategy. Zr shallow doping was introduced into Ge‐doped hematite. XPS‐depth profiling confirms a gradient distribution of Zr, incorporated via surface diffusion during high‐temperature thermal sintering. In conjunction with Ge‐doping during nucleation reaction, which promotes the photoactive H(110) plane and suppresses FTO‐induced Sn‐diffusion, Zr plays a dual role in improving bulk electronic properties while mitigating surface recombination in hematite. This synergistic effect facilitates more efficient charge transport at the electrode–electrolyte interface, as evidenced by the lowest interfacial R 2 obtained from EIS, along with reduced bulk R 1 , indicating enhanced conductivity. As a result, the photocurrent density increases from 2.06 to 2.41 mA cm −2 at 1.23 V RHE upon Zr co‐doping, even in the absence of a cocatalyst. The synergistic lattice restructuring induced by elemental co‐doping—through the selection of dopants with complementary roles—enhances carrier density without introducing excessive defect states. Consequently, bulk recombination is suppressed, and the surface becomes more favorable for hole transfer to the electrolyte.