Corson Elizabeth R, Kas Recep, Kostecki Robert, Urban Jeffrey J, Smith Wilson A, McCloskey Bryan D, Kortlever Ruud
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, California 94720, United States.
Materials for Energy Conversion and Storage (MECS), Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology, 2629 HZ Delft, The Netherlands.
J Am Chem Soc. 2020 Jun 18. doi: 10.1021/jacs.0c01953.
Illumination of a voltage-biased plasmonic Ag cathode during CO reduction results in a suppression of the H evolution reaction while enhancing CO 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 (attenuated total reflectance-surface-enhanced infrared absorption spectroscopy) study of a sputtered thin film Ag cathode on a Ge ATR crystal in CO-saturated 0.1 M KHCO over a range of potentials under both dark and illuminated (365 nm, 125 mW cm) conditions to elucidate the nature of this plasmonic enhancement. We find that the onset potential of CO reduction to adsorbed CO on the Ag surface is -0.25 V 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 V, we conclude that the light must be assisting the desorption of CO from the surface. Furthermore, the HCO wavenumber and peak area increase immediately upon illumination, precluding a thermal effect. We propose that the enhanced local electric field that results from the localized surface plasmon resonance (LSPR) is strengthening the HCO bond, further increasing the local pH. This would account for the decrease in H formation and increase the CO reduction products in the light.
在一氧化碳还原过程中，对施加电压的等离子体银阴极进行光照会抑制析氢反应，同时增强一氧化碳还原反应。这种效应已被证明是光子效应而非热效应，但确切的等离子体机制尚不清楚。在此，我们对在锗衰减全反射（ATR）晶体上溅射的薄膜银阴极进行了原位衰减全反射-表面增强红外吸收光谱（ATR-SEIRAS）研究，该阴极处于0.1 M碳酸氢钾的一氧化碳饱和溶液中，在一系列电位下，分别处于黑暗和光照（365纳米，125毫瓦/平方厘米）条件下，以阐明这种等离子体增强效应的本质。我们发现，一氧化碳在银表面还原为吸附态一氧化碳的起始电位为-0.25伏，在光照和黑暗条件下相同。由于在接近该起始电位的光照条件下检测到气态一氧化碳的生成，但在黑暗中直到-0.5伏才观察到，我们得出结论，光照必定有助于一氧化碳从表面解吸。此外，光照后碳酸氢根的波数和峰面积立即增加，排除了热效应。我们提出，由局域表面等离子体共振（LSPR）产生的增强的局部电场正在强化碳酸氢根键，进一步提高局部pH值。这可以解释光照下析氢量的减少以及一氧化碳还原产物的增加。
