Surface-Adsorbed CO as an Infrared Probe of Electrocatalytic Interfaces
Surface-Adsorbed CO as an Infrared Probe of Electrocatalytic Interfaces
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DOI：
10.1021/acscatal.0c03316
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发表时间：
2020-10-16
期刊：
影响因子：
12.9
通讯作者：
Waegele, Matthias M.
中科院分区：
文献类型：
--
作者：
Gunathunge, Charuni M.;Li, Jingyi;Waegele, Matthias M.
电催化界面使具有基础和技术意义的化学转化成为可能，这是通过其他方式难以实现的。例子包括醇的选择性氧化、1,2、生物质的转化、3,4以及二氧化碳5,6和氮的减少。然而，这些反应的电催化存在产物选择性差和催化剂失活的问题。解决这些问题需要对这些复杂的界面有更好的分子水平的理解（图1）。在电极方面，电极材料和表面形貌决定了催化活性位点的集合。5,9−12在电解质方面，决定催化作用的关键因素包括双电层中过量离子的分布，13−15电极附近的pH值，16−20界面水的结构，21,22以及表面中间体和吸附电解质离子的覆盖率。14,23界面的电解质侧以复杂的方式与电极耦合，并且在反应条件下经常演变表面形态。24−26因此，原位和操作技术是必要的，以评估电化学环境中的表面形态。在工作条件下探测界面是一个巨大的实验挑战。各种x射线技术，27,28表面增强拉曼光谱（SERS）， 6,29和表面增强红外吸收光谱（SEIRAS） 30−32已经成为特别有用的方法。虽然每种技术都有其优点和缺点，但它们通常提供互补的信息。SEIRAS的主要优势是它的高灵敏度，可以在几秒钟内收集光谱，以及它的宽光谱窗口，允许同时观察多个界面物种。在该技术中，入射红外辐射与纳米结构金属表面的相互作用会引起表面附近局部红外场的等离子体增强。33,34因此，来自表面吸附物质的红外吸收信号通常以101 - 102倍的倍数增强，对于粗金属薄膜33,34和纳米尺度天线的104 - 105倍。35,36这些改进使检测吸附物的亚单层覆盖成为可能。随着距离表面的增加，电场增强急剧衰减，通常在~ 5nm， 33,34内，从而使大块电解质种类的贡献最小化。SEIRAS是特别强大的，当它是耦合到一个合适的分子探针的界面。表面吸附CO （COads）的CO拉伸模式对外加电位、表面形貌和双电层结构敏感。COads是还原和氧化一氧化碳的中间体，在其他反应中可以作为旁观物质引入。因此，它是一种功能强大、应用广泛的电催化界面红外探针。负载在研究催化剂固/气界面表面形态方面的作用早已得到认可。40−42然而，CO拉伸光谱对COads探针局部环境的复杂依赖使得光谱的解释成为一项艰巨的任务。
Electrocatalytic interfaces enable chemical transformations of fundamental and technological significance that are challenging to achieve by other means. Examples include the selective oxidation of alcohols, 1, 2 the conversion of biomass, 3, 4 and the reduction of carbon dioxide 5, 6 and nitrogen. 7, 8 However, electrocatalysis of these reactions suffers from poor product selectivity and catalyst deactivation. Addressing these issues requires a better molecular-level understanding of these complex interfaces (Figure 1). On the electrode side, the electrode material and surface morphology determine the ensemble of catalytically active sites. 5, 9− 12 On the electrolyte side, key factors that determine the catalysis include the distribution of excess ions in the electric double layer, 13− 15 the pH in the vicinity of the electrode, 16− 20 the structure of interfacial water, 21, 22 and the coverages of surface intermediates and adsorbed electrolyte ions. 14, 23 The electrolyte side of the interface couples in intricate ways to the electrode and often evolves the surface morphology under reaction conditions. 24− 26 Therefore, in situ and operando techniques are necessary to assess the surface morphology in the electrochemical environment. Probing the interface under operating conditions is a great experimental challenge. A variety of X-ray techniques, 27, 28 surface-enhanced Raman spectroscopy (SERS), 6, 29 and surface-enhanced infrared absorption spectroscopy (SEIRAS) 30− 32 have emerged as particularly useful methods. While each of the techniques has its strengths and weaknesses, they often provide complementary information. Key strengths of SEIRAS are its high sensitivity, enabling the collection of a spectrum within a few seconds, and its broad spectral window, permitting the simultaneous observation of multiple interfacial species. In this technique, the interaction of incident IR radiation with a nanostructured metal surface gives rise to a plasmonic enhancement of the local IR field in the vicinity of the surface. 33, 34 As a result, IR absorption signals from surfaceadsorbed species are typically enhanced by factors of 101− 102 for rough metal films 33, 34 and 104− 105 for nanoscale antennas. 35, 36 These enhancements enable the detection of submonolayer coverages of adsorbates. The field enhancement steeply decays with increasing distance from the surface, typically within∼ 5 nm, 33, 34 thereby minimizing contributions from bulk electrolyte species.SEIRAS is particularly powerful when it is coupled to a suitable molecular probe of the interface. The C O stretch mode of surface-adsorbed CO (COads) is sensitive to the applied potential, surface morphology, and electric double layer structure. COads is an intermediate in the reduction 37 and oxidation of carbon monoxide 38, 39 and can be introduced as a spectator species during other reactions. Therefore, it is a powerful and broadly applicable IR probe of the electrocatalytic interface. The utility of COads for studying the surface morphology of catalysts at the solid/gas interface has long been recognized. 40− 42 However, the complex dependence of the C O stretch spectra on the local environment of the COads probe renders the interpretation of the spectra a nontrivial task.