Polyhedral silver-gold-alloy nanocrystal induced enhanced phase transition in monolayer 2H-MoS2 for electrocatalytic hydrogen evolution

We report the synthesis of unique faceted polygonal silver–gold (AgAu) nanocrystals (NCs) and their integration with CVD-grown 2D MoS2 for plasmon-induced hot-electron injection and phase transformation from the semiconducting 2H to the metallic 1T phase. The as-synthesized AgAu NCs, enriched with facets, corners, and edges, exhibited a strong multi-modal plasmonic response across the visible spectrum. Upon photoexcitation, the AgAu/MoS2 hybrid catalyst demonstrated a significant improvement in hydrogen evolution reaction (HER) activity, with the overpotential reduced by ∼ 45 % (316 mV) and the Tafel slope decreased by ∼55 % (469 mV dec−1). The enhanced catalytic performance arises from plasmon-driven 2H→1T phase transition, increased density of active sites, lowered Gibbs free energy, improved charge separation, altered surface potential, and higher electrical conductivity of MoS2. Furthermore, the photoresponse current density increased by ∼2.8 times under light irradiation compared to dark conditions. Density functional theory (DFT) calculations revealed substantial modifications in the electronic properties of the AgAu/MoS2 hybrid, including work function, surface chemical potential, and density of states, attributed to plasmonic and exchange interactions at the interface. This study establishes a promising strategy for exploiting alloy-based multipolar plasmonic NCs to accelerate HER activity in 2D transition metal dichalcogenides.