Indirect to Direct Charge Transfer Transition in Plasmon-Enabled CO₂ Photoreduction

Understanding hot carrier dynamics between plasmonic nanomaterials and its adsorbate is of great importance for plasmon-enhanced photoelectronic processes such as photocatalysis, optical sensing and spectroscopic analysis. However, it is often challenging to identify specific dominant mechanisms for a given process because of the complex pathways and ultrafast interactive dynamics of the photoelectrons. Here, using CO₂ reduction as an example, the underlying mechanisms of plasmon-driven catalysis at the single-molecule level using time-dependent density functional theory calculations is clearly probed. The CO₂ molecule adsorbed on two typical nanoclusters, Ag₂₀ and Ag₁₄₇, is photoreduced by optically excited plasmon, accompanied by the excitation of asymmetric stretching and bending modes of CO₂. A nonlinear relationship has been identified between laser intensity and reaction rate, demonstrating a synergic interplay and transition from indirect hot-electron transfer to direct charge transfer, enacted by strong localized surface plasmons. These findings offer new insights for CO₂ photoreduction and for the design of effective pathways toward highly efficient plasmon-mediated photocatalysis.