Nanogap-Resolved Adsorption-Coupled Electron Transfer by Scanning Electrochemical Microscopy: Implications for Electrocatalysis
Nanogap-Resolved Adsorption-Coupled Electron Transfer by Scanning Electrochemical Microscopy: Implications for Electrocatalysis
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DOI：
10.1021/acs.analchem.2c04008
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发表时间：
2022-12-13
影响因子：
7.4
通讯作者：
Amemiya, Shigeru
中科院分区：
文献类型：
--
作者：
Kurapati, Niraja;Janda, Donald C.;Amemiya, Shigeru
在这里，我们首次证明了吸附耦合电子转移(ACET)反应的机理可以从实验上确定。氧化还原活性分子的电子转移(ET)和特殊吸附在许多电极反应中是耦合的，具有重要的现实意义和根本意义。ACET反应通常由一个协调的机制来代表。在还原吸附中，氧化剂同时被还原，并通过ACET步骤作为还原剂吸附在电极表面。或者，当还原剂吸附是可逆的时，非协调机制分别介导外球还原和吸附。在电催化中，可逆吸附的还原剂是普遍存在的重要中间体。此外，基于ACET和外球ET步骤的混合机制使电催化变得复杂。在这项工作中，我们以简单的模型揭示了二茂铁衍生物吸附在高取向热解石墨上的非共格机理。我们使纳米扫描电化学显微镜(SECM)的瞬时伏安模式能够动力学地控制吸附步骤，这是区分非协同、协同和混合机制所必需的。通过有限元模拟，对各种机构的实验伏安曲线进行了比较。非协调机制得到支持，以表明ACET步骤本质上比其外球对应步骤慢至少四个数量级。这一发现表明，ACET步骤在热力学上是便利的，但不一定被还原剂的吸附加速或催化。基于SECM的暂态伏安法将成为在初级水平上解析和理解电催化ACET反应的有力工具。
Here, we demonstrate for the first time that the mechanism of adsorption-coupled electron-transfer (ACET) reactions can be identified experimentally. The electron transfer (ET) and specific adsorption of redox-active molecules are coupled in many electrode reactions with practical importance and fundamental interest. ACET reactions are often represented by a concerted mechanism. In reductive adsorption, an oxidant is simultaneously reduced and adsorbed as a reductant on the electrode surface through the ACET step. Alternatively, the non-concerted mechanism mediates outer-sphere reduction and adsorption separately when the reductant adsorption is reversible. In electrocatalysis, reversibly adsorbed reductants are ubiquitous and crucial intermediates. Moreover, electrocatalysis is complicated by the mixed mechanism based on simultaneous ACET and outer-sphere ET steps. In this work, we reveal the non-concerted mechanism for ferrocene derivatives adsorbed at highly oriented pyrolytic graphite as simple models. We enable the transient voltammetric mode of nanoscale scanning electrochemical microscopy (SECM) to kinetically control the adsorption step, which is required for the discrimination of non-concerted, concerted, and mixed mechanisms. Experimental voltammograms are compared with each mechanism by employing finite element simulation. The non-concerted mechanism is supported to indicate that the ACET step is intrinsically slower than its outer-sphere counterpart by at least four orders of magnitude. This finding implies that an ACET step is facilitated thermodynamically but may not be necessarily accelerated or catalyzed by the adsorption of the reductant. SECM-based transient voltammetry will become a powerful tool to resolve and understand electrocatalytic ACET reactions at the elementary level.