Plasmonic Au₃Cu Ordered Nanocrystals Induced Phase Transformation in 2D‐MoS₂ for Efficient Hydrogen Evolution

Abstract The synthesis of ordered gold‐copper (Au₃Cu) alloy nanocrystals (≈10 nm) is reported and used in the semiconductor (2H) to metallic (1T) phase transformation of an atomically thin large‐area 2D‐MoS₂ grown via CVD technique. The ordered Au₃Cu nanocrystals are dispersed over 2D‐MoS₂, and the phase transformation is confirmed via Raman spectroscopy followed by X‐ray photoelectron spectroscopy (XPS), while the surface properties of the Au₃Cu/2D‐MoS₂ is determined by the XPS valence band analysis and ultra‐violet photoemission spectroscopy (UPS). By comparing overpotential and Tafel slopes for Hydrogen Evolution Reaction (HER), a decrease is observed in overpotential by 83.2 mV and Tafel slope by ≈58.25 mV per decade for Au₃Cu/MoS₂ on light irradiation. This electrocatalytic enhancement of Au₃Cu/MoS₂ refers to the transformation of semiconducting 2D‐MoS₂ to metallic phase under light illumination, thereby altering the surface electronic structures, improving carrier concentrations, lowering the valence band edge, and lowering the free energy of H^* adsorption/desorption. Density functional theory (DFT) calculations, along with other surface characterizations, further illustrate that the ordered nanocrystal‐induced phase transformation in 2D‐MoS₂ leads to a more durable metallic characteristic, thus, enhancing the surface electrical conductivity, reducing surface potential and Gibbs free energy, and improving the kinetics of photoelectrocatalytic performance of the hybrid structure.