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

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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.

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