Uncovering Photoelectronic and Photothermal Effects in Plasmon-Mediated Electrocatalytic CO₂ Reduction

Plasmon-mediated electrocatalysis that rests on the ability of coupling localized surface plasmon resonance (LSPR) and electrochemical activation, emerges as an intriguing and booming area. However, its development seriously suffers from the entanglement between the photoelectronic and photothermal effects induced by the decay of plasmons, especially under the influence of applied potential. Herein, using LSPR-mediated CO₂ reduction on Ag electrocatalyst as a model system, we quantitatively uncover the dominant photoelectronic effect on CO₂ reduction reaction over a wide potential window, in contrast to the leading photothermal effect on H₂ evolution reaction at relatively negative potentials. The excitation of LSPR selectively enhances the CO faradaic efficiency (17-fold at -0.6 V_RHE ) and partial current density (100-fold at -0.6 V_RHE ), suppressing the undesired H₂ faradaic efficiency. Furthermore, in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveals a plasmon-promoted formation of the bridge-bonded CO on Ag surface via a carbonyl-containing C1 intermediate. The present work demonstrates a deep mechanistic understanding of selective regulation of interfacial reactions by coupling plasmons and electrochemistry.