Manipulating the Spin State of Fe Atom to Boost Surface Reaction Kinetics Toward Robust Photocatalytic Hydrogen Evolution

The photocatalytic hydrogen evolution (PHE) performance over transition metal catalysts is limited by the unsatisfactory surface catalytic reaction kinetics, which involves the transformation of electronic spin states. In this work, we successfully regulate the spin state of Fe single atoms (SAs) from a low-spin configuration (LS) to a medium-spin state (MS) via a biomineralization strategy, where the coordination configuration of Fe SAs transforms from Fe-N₄ to Fe-N₃S. This spin state transition of Fe center is able to not only influence the orbital orientation but also modulate the electronic coupling between active sites and the adsorbates, thereby enhancing the kinetic process of hydrogen evolution reaction (HER). Besides, the spin polarization induced by this unique structure could also improve the utilization efficiency of the carriers by facilitating the separation and migration of photogenerated carriers and prolonging their lifetime. All these factors directly contribute to the superior activity of Fer-N-C@ZIS (Fer, ferritin; ZIS, ZnIn₂S₄), which delivers an impressive H₂ evolution rate of approximately 31 mmol g^-1 h^-1 and a high stability over 25 h of continuous operation.