Atomically-Thin Holey 2D Nanosheets of Defect-Engineered MoN–Mo₅N₆ Composites as Effective Hybridization Matrices

The defect engineering of inorganic solids has received significant attention because of its high efficacy in optimizing energy-related functionalities. Consequently, this approach is effectively leveraged in the present study to synthesize atomically-thin holey 2D nanosheets of a MoN–Mo₅N₆ composite. This is achieved by controlled nitridation of assembled MoS₂ monolayers, which induced sequential cation/anion migration and a gradual decrease in the Mo valency. Precise control of the interlayer distance of the MoS₂ monolayers via assembly with various tetraalkylammonium ions is found to be crucial for synthesizing sub-nanometer–thick holey MoN–Mo₅N₆ nanosheets with a tunable anion/cation vacancy content. The holey MoN–Mo₅N₆ nanosheets are employed as efficient immobilization matrices for Pt single atoms to achieve high electrocatalytic mass activity, decent durability, and low overpotential for the hydrogen evolution reaction (HER). In situ/ex situ spectroscopy and density functional theory (DFT) calculations reveal that the presence of cation-deficient Mo₅N₆ domain is crucial for enhancing the interfacial interactions between the conductive molybdenum nitride substrate and Pt single atoms, leading to enhanced electron injection efficiency and electrochemical stability. The beneficial effects of the Pt-immobilizing holey MoN–Mo₅N₆ nanosheets are associated with enhanced electronic coupling, resulting in improvements in HER kinetics and interfacial charge transfer.