Mu Shijia, Li Lei, Zhao Ruijuan, Lu Honglei, Dong Huilong, Cui Chunhua
Molecular Electrochemistry Laboratory, Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, Chengdu 610054, China.
School of Materials Engineering, Changshu Institute of Technology, Changshu, Jiangsu 215500, China.
ACS Appl Mater Interfaces. 2021 Oct 13;13(40):47619-47628. doi: 10.1021/acsami.1c13529. Epub 2021 Sep 28.
Depressing the competitive hydrogen evolution reaction (HER) to promote current efficiency toward carbon-based chemicals in the electrocatalytic CO reduction reaction (CORR) is desirable. A strategy is to apply the hydrophobically molecular-modified electrodes. However, the molecular-scale catalytic process remains poorly understood. Using alkanethiol-modified hydrophobic Cu as an electrode and CO-saturated KHCO as an electrolyte, we reveal that HO, rather than HCO, is the major H source for the HER, determined by differential electrochemical mass spectrometry with isotopic labeling. As a result, using in situ Raman, we find that the hydrophobic molecules screen the cathodic electric field effect on the reorientation of interfacial HO to a "H-down" configuration toward Cu surfaces that corresponds to the decreased content of H-bonding-free water, leading to unfavorable HO dissociation and thus decreased H source for the HER. Further, density functional theory calculations suggest that the absorbed alkanethiol molecules alter the electronic structure of Cu sites, thus decreasing the formation energy barrier of CORR intermediates, which consequently increases the CORR selectivity. This work provides a molecular-level understanding of improved CORR on hydrophobically molecule-modified catalysts and presents general references for catalytic systems having HO-involved competitive HER.
抑制竞争性析氢反应（HER）以提高电催化CO还原反应（CORR）中生成碳基化学品的电流效率是很有必要的。一种策略是应用疏水分子修饰电极。然而，分子尺度的催化过程仍知之甚少。我们以烷硫醇修饰的疏水铜作为电极，以CO饱和的KHCO作为电解质，通过同位素标记的差分电化学质谱法确定，HER的主要氢源是HO而非HCO。结果，通过原位拉曼光谱，我们发现疏水分子屏蔽了阴极电场对界面HO重新定向至朝向铜表面的“氢向下”构型的影响，这对应于无氢键水含量的降低，导致不利的HO解离，从而减少了HER的氢源。此外，密度泛函理论计算表明，吸附的烷硫醇分子改变了铜位点的电子结构，从而降低了CORR中间体的形成能垒，进而提高了CORR的选择性。这项工作提供了对疏水分子修饰催化剂上CORR改善的分子水平理解，并为涉及HO的竞争性HER催化体系提供了一般参考。
