Interstitial carbon doping synergistically boosts bulk charge transport and surface OER kinetics of α-Fe2O3 photoanodes

Photoelectrochemical (PEC) water splitting using α-Fe 2 O 3 photoanodes is severely limited by poor bulk charge transport and sluggish surface oxygen evolution reaction (OER) kinetics. Herein, we report a novel interstitial carbon doping strategy via glucose-assisted hydrothermal synthesis and annealing to synergistically address these bottlenecks. Unlike conventional carbon modifications (surface coating, which only improves interfacial properties, or substitutional doping, which induces lattice distortion), interstitial carbon doping simultaneously enhances bulk charge transport and surface OER activity without structural compromise. Specifically, interstitial C atoms induce lattice compression (confirmed by XRD peak shifts), increase carrier density to 2.57 × 10 18 cm -3 (6.2-fold higher than pristine α-Fe 2 O 3 ), and reduce electron transport time to 0.20 ms, while surface C-O/C=O groups accelerate OER kinetics by facilitating intermediate adsorption. The optimized C50-α-Fe 2 O 3 photoanode exhibits a photocurrent density of 1.80 mA/cm 2 at 1.23 V vs. RHE (6.3-fold enhancement), an onset potential negatively shifted to 0.82 V vs. RHE, and a maximum applied bias photon-to-current efficiency (ABPE) of 0.21 % at 1.02 V vs. RHE. This work demonstrates interstitial doping as a versatile approach to decouple bulk/surface property optimization, advancing α-Fe 2 O 3 for efficient solar-to-hydrogen (STH) conversion.