Distorted Ge–O–Fe Microstructure as an Active Unit in Hematite to Accelerate Solar Water Splitting

The local atomic structure in hematite determines its intrinsic property for photoelectrochemical water splitting, but its precise design has rarely been clearly demonstrated. Here by inserting Ge atoms into a hematite lattice with abundant vacancies, the local environment around Fe can be significantly modulated with the formation of a distorted Ge–O–Fe microstructure, which serves as an active catalytic unit to lower the energy barrier for an efficient oxygen evolution reaction. As a result, the optimized Ge–Fe 2 O 3 (LV) photoanode exhibits an excellent photocurrent density of 4.04 mA/cm 2 at 1.23 V RHE, which is 5.0 times higher than that of pristine Fe 2 O 3 (0.80 mA/cm 2 ). It can further achieve 5.09 mA/cm 2 at 1.23 V RHE (stable over 100 h) by coupling with FeNiOOH. Furthermore, when connecting the Ge-based hematite with a commercial solar cell, the all-solar-driven system can realize an outstanding solar-to-hydrogen efficiency of up to 5.3%, standing for the top value for hematite-based systems. The Ge–O–Fe unit induced catalytic performance enhancement may shed light on the design of efficient catalysts for solar water splitting.