Synergistic Ge–Ta co-doping and Al shallow diffusion enable lattice reordering to enhance charge transport in hematite photoanodes

Hematite suffers from slow charge transport and high electron–hole recombination, which limit its photoelectrochemical (PEC) performance. In this work, we systematically investigate lattice structural reordering in hematite through the incorporation of heterogeneous multivalent metal ions and elucidate their synergistic effects. Incorporation of Ge⁴⁺ enhances bulk charge transport by increasing the electrical conductivity of the hematite lattice. Upon co-incorporation of Ta⁵⁺ with Ge, charge compensation induces partial reduction of Ge⁴⁺ to Ge³⁺, leading to an increased current density of ∼2.11 mA cm⁻² at water-oxidation potentials. Al³⁺ ions detected by depth profiling, typically associated with shallow surface diffusion, exhibit a dual role in the Ge–Ta system by simultaneously improving bulk charge transport and interfacial charge transfer at the hematite–electrolyte interface. This results in a 2.6-fold enhancement in current density compared to bare hematite (0.91 mA cm⁻²). Further integration of a cocatalyst yields a stable current density of ∼2.60 mA cm⁻² at 1.23 V_RHE, along with robust gas evolution kinetics and a faradaic efficiency of 95%, approaching the theoretical value for hydrogen generation. Structural, electrochemical, and kinetic analyses using XRD, EIS, and IMPS confirm that the Al/Ge–Ta:Fe₂O₃/FTO photoanode exhibits enhanced lattice reordering, reduced charge-transfer resistance, and accelerated electron–hole transport dynamics, enabling efficient and sustained water oxidation.