Photocatalytic overall water splitting (OWS) is an appealing strategy to convert solar energy and produce hydrogen fuel. NiTiO3 (NTO) is an earth‐abundant material, which is studied as a robust photocatalyst with broad absorptance of sunlight spectrum, ranging from ultraviolet to infrared regions. Herein, by a rational design of an NTO‐based photocatalytic system, the activity for photocatalytic OWS is realized under both ultraviolet and visible light illuminations, and H2 and O2 evolution is achieved within the stoichiometric ratio of 2:1. Specifically, Gallium is doped into the NTO crystal to activate the material for photocatalytic OWS by improving photoexcited charge migration. Meanwhile, Co and Pt species are screened out as the oxygen evolution and hydrogen evolution co‐catalysts, respectively. Theoretical stimulations, steady state experiments, and operando characterizations are acquired to investigate the OWS performance. This research paves the pathway to apply this small‐bandgap photocatalyst for OWS by maximizing the solar energy harvesting.

With the advantage of excellent light absorption ability and earth-abundant elements, Cu2ZnSnS4 (CZTS) is widely applied in the photoelectrochemical (PEC) reduction of CO2. However, the microscopic mechanism of the CO2 conversion on CZTS is still unclear. Here, we have theoretically investigated the electronic properties of the CZTS to reveal the special bonding properties of CO2 under both exposed metal and sulfur terminations of the CZTS and the formation mechanisms of producing CO, HCOOH, and CH4 from a microscopic perspective. Our study shows that when the metal is exposed to the surface, CO2 will convert to HCOOH with a high selectivity with the limiting potential of 0.23 V (vs RHE). However, on the sulfur termination, the onset potentials of producing HCOOH, CO, and CH4 are all lower than 0.4 V, indicating the mix formations. These findings provide theoretical insight into the PEC experiments of CO2 reduction on CZTS.