Field‐Directed Growth of Hematite for Advanced Solar Hydrogen Production

Interplay of magnetic susceptibility and vapor phase nucleation in magnetic field‐assisted chemical vapor deposition (mf‐CVD) enables precise control over phase evolution, crystallographic orientation, and surface texturing in metal oxide thin films. The synthesis of hematite (α‐Fe 2 O 3 ) thin films via chemical vapor deposition using [Fe 2 (O t Bu) 6 ] as a molecular precursor is reported. Applying an external magnetic field (1 T) during deposition significantly alters the microstructure of the hematite films, reflected in superior photoelectrochemical (PEC) performance. Relative to zero‐field deposition, mf‐CVD increased the photocurrent density of hematite by 74%, attributed to magnetically induced texturing and densification, both enhancing charge separation and transfer efficiencies. Magnetic field‐assisted hematite growth also increases the electrochemically active surface area, while a 33 mV photovoltage gain suggests a stronger built‐in electric field in the α‐Fe 2 O 3 ‐1 T film. Electrochemical impedance spectroscopy further confirms a reduced surface state density supporting improved interfacial charge dynamics. Furthermore, the magnetically altered material exhibits remarkable stability for 100 h of PEC operation. The results highlight hematite as a model photoanode for elucidating how magnetic fields modulate active domains in metal oxides, offering an innovative process to transform materials through applied fields.