Illumination of a voltage-biased plasmonic Ag cathode during CO2 reduction results in a suppression of the H2 evolution reaction while enhancing CO2 reduction. This effect has been shown to be photonic rather than thermal, but the exact plasmonic mechanism is unknown. Here, we conduct an in situ ATR-SEIRAS study of a sputtered thin film Ag cathode on a Ge ATR crystal in CO2-saturated 0.1 M KHCO3 over a range of potentials in both dark and illuminated (365 nm, 125 mW cm-2) conditions to elucidate the nature of this plasmonic enhancement. We find that the onset potential of CO2 reduction to adsorbed CO on the Ag surface is -0.25 VRHE and is identical in the light and the dark. As the production of gaseous CO is detected in the light near this onset potential but is not observed in the dark until -0.5 VRHE we conclude that the light must be assisting the desorption of CO from the surface. Furthermore, the HCO3- wavenumber and peak area increase immediately upon illumination, precluding a thermal effect. We propose that the enhanced local electric field that results from the LSPR is strengthening the HCO3- bond to the surface, further increasing the local pH. This would account for the decrease of H2 formation and increase of CO2 reduction products in the light.

中文翻译：

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在等离子银阴极还原二氧化碳的原位 ATR-SEIRAS

在 CO2 还原过程中照射偏压等离子体 Ag 阴极会抑制 H2 析出反应，同时增强 CO2 还原。这种效应已被证明是光子效应而不是热效应，但确切的等离子体机制尚不清楚。在这里，我们对在 CO2 饱和的 0.1 M KHCO3 中的 Ge ATR 晶体上的溅射薄膜 Ag 阴极进行了原位 ATR-SEIRAS 研究，该阴极在黑暗和照明下的一系列电位（365 nm，125 mW cm-2）阐明这种等离子体增强的性质的条件。我们发现 CO2 还原为 Ag 表面吸附 CO 的起始电位为 -0.25 VRHE，并且在明暗条件下相同。由于在此起始电位附近的光中检测到气态 CO 的产生，但直到 -0 才在黑暗中观察到。5 VRHE 我们得出结论，光必须有助于从表面解吸 CO。此外，HCO3- 波数和峰面积在光照后立即增加，排除了热效应。我们提出，由 LSPR 产生的增强的局部电场正在加强与表面的 HCO3-键，进一步增加局部 pH 值。这将解释光中 H2 形成的减少和 CO2 还原产物的增加。