Confined Synthesis of 2D Molybdenum Diphosphide Nanosheets via Gas-Solid Transformation

Molybdenum diphosphide (MoP₂), a topological semimetal, possesses distinctive properties and applications in catalysis, energy storage, and condensed matter physics. However, synthesizing high-purity MoP₂ is complex and often results in undesired stoichiometric by-products. Additionally, the intrinsic orthorhombic crystal structure makes it difficult to synthesize MoP₂ in a 2D morphology, which is desirable for device and energy applications. Here, the robust synthesis of MoP₂ with a well-defined 2D morphology is achieved using the confined gas-solid phosphorization of a MoS₂ precursor on substrates. The use of 2D precursors and the surface confinement provided by the substrate maintain the 2D morphology and result in a thickness-dependent stoichiometry of the phosphorization products. The chemical composition and crystal structure of MoP₂ nanosheets are comprehensively characterized. At room temperature, MoP₂ nanosheets exhibit metallic transport with high conductivity over 5500 S cm^-1. Furthermore, MoP₂ nanosheets demonstrate excellent electrocatalytic activity and durability for hydrogen evolution in both neutral and acid mediums. Notably, MoP₂ nanosheets possess better durability than amorphous Pt film and commercial Pt/C, positioning MoP₂ as a promising catalyst for hydrogen evolution in neutral mediums. This work advances the synthetic chemistry of 2D MoP₂ and provides 2D semimetals with a novel member for future explorations in diverse fields.