Electric double layers (EDLs) at the electrode-electrolyte interface are key to electrochemical energy conversion and storage applications. To date, most of the existing spectroscopy and atomistic imaging methods, including X-ray spectroscopy and electron microscopy, can only probe the overall chemical states and/or the planar distribution of strongly adsorbed species at the electrode interface, therefore the molecular scale structure of EDLs still remains elusive. Here, we use an electrochemical three-dimensional atomic force microscopy (EC-3D-AFM), to achieve 3D imaging of the molecular scale EDL structure of an ionic liquid with a high viscosity on heterogeneous electrode materials. Rich 3D molecular distribution profiles and potential-dependent reconfigurations are observed and confirmed with molecular dynamics simulations, offering us molecular level understandings of the capacitive charging effects for different electrode systems. We expect this mechanistic understanding to serve as design rules for applications such as supercapacitors and batteries.

Three-dimensional molecular mapping of ionic liquids at electrified interfaces

ACS Spring 2022

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