Electronic State Modulation Interfaced With Interfacial Electric Fields: Ca Site Activation Promoting Photocatalytic Hydrogen Evolution in CdS/Ca 2 Co 2 O 5 S‐Scheme Heterojunction

The photocatalytic hydrogen evolution technology presents a green and sustainable solution for alleviating the energy crisis. Nevertheless, single‐phase semiconductors are confronted with severe photogenerated carrier recombination and insufficient active sites, which act as bottlenecks. This study innovatively designed and established a CdS/Ca 2 Co 2 O 5 S‐scheme heterojunction. Through electrostatic self‐assembly and the solvothermal method, a close interfacial contact was realized. By systematically integrating in situ XPS and DFT calculations, the formation mechanism of the interfacial electric fields at the interface and the directional migration path of photogenerated charges were thoroughly revealed. The theoretical calculations innovatively identified that the Ca atom was the main active site for hydrogen evolution, and the d‐band center regulation adjusted Δ G H* from −0.53 to 0.02 eV, significantly lowering the reaction energy barrier. The hydrogen evolution rate of CC20% composite catalyst reaches 14.6 mmol g −1 h −1 , which was 4.9 times that of CdS and demonstrated excellent photochemical stability. This work offers a new approach for the development of efficient cobalt‐based perovskite derivative photocatalytic materials.