Short-Range Ordered Dual-Elemental Doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Splitting

The performance of hematite photoanodes for photoelectrochemical (PEC) water splitting is highly dependent on their microstructures and surface states. Here, we reveal that rapid microwave sintering induces short-range ordered doping of Sn and Ti elements at the atomic scale via aberration-corrected transmission electron microscopy (AC-TEM), revealing segregation of the same dopant species. Photoelectrochemical impedance spectroscopy (PEIS), intensity-modulated photocurrent spectroscopy (IMPS), operando transient absorption spectroscopy (TAS), and density functional theory (DFT) together indicate that the alteration of the atomic structure significantly modulates the distribution of surface states, thereby suppressing surface charge recombination and further enhancing the PEC performance. The optimized hematite photoanode exhibits a photocurrent density of 3.57 mA cm^-2 at 1.23 V vs RHE, which is 4.2 times of pristine hematite (0.85 mA cm^-2). When coupled with NiFeOOH, the photocurrent density further increases to 3.96 mA cm^-2, along with a cathodic shift in the onset potential from 0.84 to 0.78 V vs RHE. Our findings examine the role of short-range order of Ti and Sn doping elements and their influence on surface state modification and PEC performance, indicating the importance of atomic-level regulation in elemental doping for enhancing PEC water splitting efficiency.