Mechanistic and DFT Insights Into Co‐Catalytic MgFe‐LDH/Hematite Interfaces for Efficient Photoelectrochemical Water Oxidation

Layered double hydroxides (LDHs) are low-cost and versatile materials, many of which are well-established water oxidation electrocatalysts. A simple MgFe-LDH variant, synthesized as size-tunable nanosheets, was successfully decorated on the surface of hematite (α-Fe₂O₃) nanorods to structure an integrating photoanode for improved photoelectrochemical (PEC) water oxidation. Combined XPS and SEM analysis showed that MgFe-LDH decoration does not interfere with the nanostructure of the light-harvesting α-Fe₂O₃. However, intensified Raman bands for the decorated α-Fe₂O₃ pointed to enhanced interactions between MgFe-LDH and α-Fe₂O₃. Optimization of the surface amount for MgFe-LDH can lead to a 340 mV cathodic shift in the onset potential at 0.1 mA cm^-2. Mott-Schottky analysis and electrochemical impedance spectroscopy further revealed that LDH decoration enhances the photogenerated charge-carrier separation and efficiently consumes holes accumulating at the electrode surface. Furthermore, density functional theory (DFT) calculations suggest a lower Gibbs free energy (ΔG) value of 1.35 eV for MgFe-LDH/α-Fe₂O₃ contrasted to pristine α-Fe₂O₃ (ΔG of 1.46 eV) for the rate-determining step (RDS), further indicating that the MgFe-LDH co-catalyst lowers the activation energy barrier for the OER. This work offers a promising method for designing high-efficiency and low-cost hematite-based photoanodes for solar-fuel devices relying on noncritical elements.