LAUSR

Solar hydrogen (H2) generation via photocatalytic water splitting is practically promising, environmentally benign, and sustainably carbon neutral. It is important therefore to understand how to controllably engineer photocatalysts at the atomic level. In this work, atomic‐level engineering of defected ReSe2 nanosheets (NSs) is reported to significantly boost photocatalytic H2 evolution on various semiconductor photocatalysts including TiO2, CdS, ZnIn2S4, and C3N4. Advanced characterizations, such as atomic‐resolution aberration‐corrected scanning transmission electron microscopy (AC‐STEM), synchrotron‐based X‐ray absorption near edge structure (XANES), in situ X‐ray photoelectron spectroscopy (XPS), transient‐state surface photovoltage (SPV) spectroscopy, and transient‐state photoluminescence (PL) spectroscopy, together with theoretical computations confirm that the strongly coupled ReSe2/TiO2 interface and substantial atomic‐level active sites of defected ReSe2 NSs result in the significantly raised activity of ReSe2/TiO2. This work not only for the first time realizes the atomic‐level engineering of ReSe2 NSs as a versatile platform to significantly raise the activities on different photocatalysts, but, more importantly, underscores the immense importance of atomic‐level synthesis and exploration on 2D materials for energy conversion and storage.