In Situ Observed Local Structural Distortions Boost Solar Water Splitting in Hematite

Although hematite (α-Fe 2 O 3 ) is considered a promising photoanode material for photoelectrochemical (PEC) water splitting, its practical application is limited by inherently low charge transport efficiency and sluggish oxygen evolution reaction (OER) kinetics. In this study, in situ synchrotron X-ray absorption spectroscopy (XAS) was employed under illumination to distinctly observe the transient electronic structure changes at Fe sites and to elucidate their structure–activity relationship with the stretching of Fe–O bond. It is revealed that local distortions induced by Fe–O bond stretching enhance the hybridization of O 2p-Fe 3d orbitals, promote electron transfer, and facilitate the formation of Fe 4+ active sites. Such structural modulation significantly suppresses surface charge recombination, thus accelerating the OER kinetics. Leveraging this mechanism, an In-Fe 2 O 3 (LV) photoanode was constructed, delivering a photocurrent density of 3.66 mA cm –2 at 1.23 V RHE, with an onset potential negatively shifted to 0.86 V RHE . Upon coupling with a FeNiOOH cocatalyst, the photocurrent density is further enhanced to 4.32 mA cm –2, and the onset potential is reduced to 0.77 V RHE . This study employs atomic-scale in situ characterization to systematically elucidate the structure–activity relationship between local lattice distortions and enhanced OER performance, providing actionable insights and strategies for the rational design of high-efficiency photoanodes.