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Existence of an Electrochemically Inert CO Population on Cu Electrodes in Alkaline pH
ACS Catalysis ( IF 12.9 ) Pub Date : 2018-07-06 00:00:00 , DOI: 10.1021/acscatal.8b01552
Charuni M. Gunathunge 1 , Vincent J. Ovalle 1 , Yawei Li 2 , Michael J. Janik 2 , Matthias M. Waegele 1
Affiliation  

Surface-adsorbed CO is generally considered a reactive on-pathway intermediate in the aqueous electrochemical reduction of CO2 on Cu electrodes. Though CO can bind to a variety of adsorption sites (e.g., atop or bridge), spectroscopic studies of the Cu/electrolyte contact have mostly been concerned with atop-bound CO. Using surface-selective infrared (IR) spectroscopy, we have investigated the reactivities and coverages of atop- and bridge-bound CO on a polycrystalline Cu electrode in contact with alkaline electrolytes. We show here that (1) a fraction of atop-bound CO converts to bridge-bonded CO when the total CO coverage drops below the saturation coverage and (2) unlike atop-bound CO, bridge-bonded CO is an unreactive species that is not reduced at a potential of −1.75 V vs SHE. Our results suggest that bridge-bonded CO is not an on-pathway intermediate in CO reduction. Using density functional theory (DFT) calculations, we further reveal that the activation barrier for the hydrogenation of bridge-bonded CO to surface-adsorbed formyl on Cu(100) is higher than that of the reduction of atop-bound CO, in qualitative agreement with our experimental findings. The possible modulation of the catalytic properties of the interface by the electrochemically inert bridge-bonded CO population should be considered in future studies involving CO2 or CO reduction on Cu under alkaline conditions.

中文翻译:

碱性pH下Cu电极上电化学惰性CO的存在

在CO 2的水性电化学还原中,表面吸附的CO通常被认为是反应途中的中间体在铜电极上。尽管CO可以结合到各种吸附位点(例如,顶部或桥键),但对Cu /电解质接触的光谱研究主要与顶部结合的CO有关。使用表面选择性红外(IR)光谱,我们研究了与碱性电解质接触的多晶铜电极上顶部和桥键结合的CO的反应性和覆盖率。我们在这里显示(1)当总的CO覆盖率降至饱和覆盖率以下时,一部分顶部键合的CO转化为桥键合的CO;(2)与顶部键合的CO不同,桥键合的CO是一种不活泼的物种,即与SHE相比,电位为-1.75 V时不会降低。我们的结果表明,桥键合的CO并不是减少CO的途中中间体。使用密度泛函理论(DFT)计算,我们进一步揭示,Cu(100)上桥键合的CO氢化成表面吸附的甲酰的氢化反应的活化势垒比顶部结合的CO还原的活化势垒要高,这与我们的实验结果在质量上是一致的。在涉及CO的未来研究中,应考虑电化学惰性桥键连接的CO族对界面催化性能的可能调节。2或在碱性条件下将Cu还原为CO。
更新日期:2018-07-06
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