Hierarchically stabilized Pt single-atom catalysts induced by an atomic substitution strategy for an efficient hydrogen evolution reaction

Tuning and stabilizing the chemical microenvironment of Pt-based single-atom catalysts is a major challenge in promoting an electrocatalytic hydrogen evolution reaction (HER). Herein, we constructed a hierarchical stabilization system of Pt single-atoms via defect substitution using the polyoxometalate (POM) (NH₄)₄[ZnMo₆O₂₄H₆] (ZnMo₆) as a template. The well-defined structure of ZnMo₆ led to precise local Zn sublimation during the formation of Mo₂C, which was converted from the Mo₆ ring in situ. The localized defect provides a well-defined Mo(C)-Pt-N coordination environment to trap Pt single-atoms. The obtained single-atom catalyst (Pt_SA@Mo₂C@NC) exhibited a superior and stable electrochemical HER performance with an unprecedented mass activity of 75.21 A mg_Pt⁻¹ in 0.5 M H₂SO₄. In-depth theoretical calculation analysis revealed that Mo(C)-Pt-N coordination provides a moderated charge state and low d-band center of the Pt site, thus significantly promoting proton adsorption and H₂ desorption. This work demonstrates a promising single-atom stabilization strategy for constructing high-performance HER electrocatalysts through the precise modulation of a three-dimensional chemical environment.