Synergizing plasmonic Au nanocages with 2D MoS₂ nanosheets for significant enhancement in photocatalytic hydrogen evolution

Plasmonic enhancement of photocatalytic hydrogen evolution has been achieved under visible light illumination by integrating strongly plasmonic metal particles such as gold (Au) with semiconducting materials. To understand the effect of plasmon resonance on the photocatalytic hydrogen evolution reaction (HER), in this work, we study the hydrogen evolution reaction (HER) over Au nanocages with systematically tunable localized surface plasmon resonance (LSPR) properties dispersed on an Al₂O₃ support and covered with multiphasic 2D MoS₂ nanosheets. It is interesting to observe that by tuning the LSPR wavelength of Au nanocages, an optimal enhancement in the photocatalytic HER can be obtained over the multiphasic 2D MoS₂ nanosheets. In particular, when the LSPR wavelength of Au nanocages is close to the absorption edge of MoS₂ nanosheets, a 40-fold increase is observed in the HER rate regarding bare MoS₂. Time-resolved transient absorption spectroscopy was conducted to explicitly identify the mechanisms behind the Au/MoS₂ system. The results suggest that near field enhancement (NFE) is the dominant LSPR process in this system and a detailed explanation of the working mechanism in this system is proposed. Governed by the NFE process, the energy of the surface plasma is transferred from Au nanocages to MoS₂ nanosheets to promote electron-hole excitation in MoS₂, and the efficiency reaches the maximum when the LSPR wavelength of Au nanocages matches the MoS₂ light absorption edge, resulting in a significantly enhanced photocatalytic hydrogen yield compared to the bare MoS₂ nanosheets and Au/MoS₂ systems where the LSPR wavelengths of Au nanocages and MoS₂ nanosheet absorption edge do not match. The learning from this work provides insights into the design of highly efficient photocatalysts based on plasmonic materials.