True co-catalytic integration of MgFe-LDH with hematite for high-efficiency photoelectrochemical water oxidation

Layered double hydroxides (LDHs) are versatile and inexpensive materials, many of which have long known as robust water oxidation electrocatalysts. A simple variant, MgFe-LDH in the form of nanosheets, adjustable in size has been 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/cm2. 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 1.37 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 non-critical elements.