Directly observing active surface intermediates represents a major challenge in electrocatalysis, especially for CO₂ electroreduction on Au. We use in-situ, plasmon-enhanced vibrational sum frequency generation spectroscopy, which has detection limits of <1% of a monolayer and can access the Au/electrolyte interface during active electrocatalysis in the absence of mass transport limitations. Measuring the potential-dependent surface coverage of atop CO confirms that the rate-determining step for this reaction is CO₂ adsorption. An analysis of the interfacial electric field reveals the formation of a dense cation layer at the electrode surface, which is correlated to the onset of CO production. The Tafel slope increases in conjunction with the field saturation due to active site blocking by adsorbed cations. These findings show that CO₂ reduction is extremely sensitive to the potential-dependent structure of the electrochemical double layer and provides direct observation of the interfacial processes that govern these kinetics.

中文翻译：

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对金上二氧化碳电还原的直接观察：船尾层的位点阻塞控制了CO2的吸附动力学。

直接观察活性表面中间体代表了电催化中的主要挑战，特别是对于在Au上进行CO ₂电还原而言。我们使用原位等离子体增强的振动和频率生成光谱，其检测限小于单层的1％，并且在没有质量传输限制的情况下，在主动电催化过程中可以访问Au /电解质界面。测量取决于电势的顶部CO的表面覆盖率可确定该反应的速率确定步骤为CO ₂吸附。界面电场的分析表明，在电极表面形成了致密的阳离子层，这与CO产生的开始有关。由于活性部位被吸附的阳离子阻止，Tafel斜率与场饱和一起增加。这些发现表明，CO ₂还原对电化学双层的电势依赖性结构极为敏感，并且可以直接观察控制这些动力学的界面过程。