Zhou Shan, Panse Kaustubh S, Motevaselian Mohammad Hossein, Aluru Narayana R, Zhang Yingjie
Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois 61801, United States.
Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, United States.
ACS Nano. 2020 Dec 22;14(12):17515-17523. doi: 10.1021/acsnano.0c07957. Epub 2020 Nov 23.
Electric double layers (EDLs), occurring ubiquitously at solid-liquid interfaces, are critical for electrochemical energy conversion and storage processes such as capacitive charging and redox reactions. However, to date the molecular-scale structure of EDLs remains elusive. Here we report an advanced technique, electrochemical three-dimensional atomic force microscopy (EC-3D-AFM), and use it to directly image the molecular-scale EDL structure of an ionic liquid under different electrode potentials. We observe not only multiple discrete ionic layers in the EDL on a graphite electrode but also a quasi-periodic molecular density distribution within each layer. Furthermore, we find pronounced 3D reconfiguration of the EDL at different voltages, especially in the first layer. Combining the experimental results with molecular dynamics simulations, we find potential-dependent molecular redistribution and reorientation in the innermost EDL layer, both of which are critical to EDL capacitive charging. We expect this mechanistic understanding to have profound impacts on the rational design of electrode-electrolyte interfaces for energy conversion and storage.
电双层（EDLs）普遍存在于固液界面，对于诸如电容充电和氧化还原反应等电化学能量转换和存储过程至关重要。然而，迄今为止，电双层的分子尺度结构仍然难以捉摸。在此，我们报告一种先进技术，即电化学三维原子力显微镜（EC-3D-AFM），并使用它直接成像在不同电极电位下离子液体的分子尺度电双层结构。我们不仅观察到石墨电极上电双层中的多个离散离子层，还观察到每层内的准周期性分子密度分布。此外，我们发现在不同电压下电双层有明显的三维重构，尤其是在第一层。将实验结果与分子动力学模拟相结合，我们发现在最内层电双层中存在电位依赖的分子重新分布和重新取向，这两者对于电双层电容充电都至关重要。我们期望这种机理理解对用于能量转换和存储的电极 - 电解质界面的合理设计产生深远影响。
