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. Atomically‐thin holey 2D nanosheets of defect‐engineered Mo5N6–MoN nanocomposites are synthesized by controlled nitridation of organic‐assembled MoS2 nanosheets. The basal expansion of MoS2 nanosheets is crucial in stabilizing sub‐nanometer–thick holey Mo5N6–MoN nanocomposite. The immobilization of Pt single atoms on holey Mo5N6–MoN nanosheet yields high‐performance electrocatalysts with high mass activity due to enhanced interfacial interaction with Mo‐deficient Mo5N6 domains.