Promoting photocarrier separation for photoelectrochemical water splitting in α-Fe₂O₃@C

Core-shell-nanostructured hematite@graphite (α-Fe₂O₃@C) for photoelectrochemical (PEC) water splitting was innovatively prepared from graphite-encapsulated iron (Fe@C) nanoparticles by the arc-discharge method. The graphite was successfully controlled from dozens to few layers, and Fe was transformed into α-Fe₂O₃ with particle size of 20–30 nm during the thermal oxidation. α-Fe₂O₃@C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy techniques. The photocurrent density of α-Fe₂O₃@C reached a maximum of 20 μA/cm² at 1.23 V_RHE when there were 2–3 layers of graphite and the film thickness was 200 nm. Herein, graphite was proven to play the key role in coupling between light blocking and enhanced photocarrier separation rather than changing the density of the oxygen vacancies. The addition of graphite layers enhanced the photocurrent density by 20 times compared with that of the bare α-Fe₂O₃ particle film derived from the hydrothermal method, which was further demonstrated by electrochemical impedance spectra (EIS).