Electrochemical reduction is a promising way to make use of CO₂ as feedstock for generating renewable fuel and valuable chemicals. Several metals can be used as the electrocatalyst to generate CO and formic acid, but hydrogen formation is an unwanted side reaction that can even be dominant. The lack of selectivity is, in general, a significant problem, but silver-based electrocatalysts have been shown to be highly selective, with faradaic efficiency of CO production exceeding 90%, when the applied voltage is below −1 V vs RHE. In this voltage range, only a small amount of hydrogen and formate is formed. We present calculations of the activation free energy for the various elementary steps as a function of applied voltage at the three low index facets, Ag(111), Ag(100) and Ag(110), as well as experimental measurements on polycrystalline electrodes, to identify the reason for this high selectivity. The formation of formic acid is suppressed, even though it is thermodynamically favored, because of the low coverage of adsorbed hydrogen and kinetic hindrance to the formation of the HCOO* intermediate, while *COOH, a key intermediate in CO formation, is thermodynamically unstable until the applied voltage reaches −1 V vs RHE, at which point the kinetics for its formation are more favorable than for hydrogen. The calculated results are consistent with experimental measurements carried out for acidic conditions and provide an atomic scale insight into the high CO selectivity of silver-based electrocatalysts.

中文翻译：

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由于电压依赖性动力学和热力学之间的相互作用，银电极对 CO2 电还原中的 CO 具有高度选择性


电化学还原是利用 CO₂ 作为原料生产可再生燃料和有价值化学品的一种很有前途的方法。几种金属可以用作电催化剂来生成 CO 和甲酸，但氢的形成是一个不需要的副反应，甚至可以占主导地位。一般来说，缺乏选择性是一个重大问题，但银基电催化剂已被证明具有高度选择性，当施加的电压低于 -1 V vs RHE 时，一氧化碳产生的法拉第效率超过 90%。在此电压范围内，仅形成少量氢气和甲酸盐。我们提出了各种基本步骤的活化自由能计算，作为三个低折射率面 Ag（111）、Ag（100） 和 Ag（110） 处施加电压的函数，以及多晶电极的实验测量，以确定这种高选择性的原因。甲酸的形成受到抑制，尽管它在热力学上受到青睐，因为吸附氢的覆盖率低，并且动力学阻碍了 HCOO* 中间体的形成，而 *COOH 是 COO 形成的关键中间体，在施加的电压达到 -1 V vs RHE 之前，热力学上不稳定，此时其形成的动力学比氢更有利。计算结果与在酸性条件下进行的实验测量一致，并为银基电催化剂的高 CO 选择性提供了原子级的见解。