Structure and Dynamics of Electric Double Layer

The electric double layer (EDL) is a fundamental component of electrode/electrolyte interfaces that governs many key electrochemical processes, including charge transport across interfaces, passivation of solid-electrolyte interphases, and chemical stability of the electrolyte. More than a century of study has yielded general models for the ion distribution through the EDL, yet little experimental evidence for the speciation, uniformity, and dynamics of the potential-dependent EDL structure is available due, in part, to the challenges with experimentally probing buried interfaces in situ. I present an investigation of the potential-dependent structure and chemistry of the EDL formed between single crystal conductive electrodes and aqueous electrolytes spanning a diverse range of compositions, ions, and concentration, including BaCl2 and CsCl. Synchrotron X-ray reflectivity and resonant anomalous X-ray reflectivity reveal distinct ion distributions that evolve as a function of potential. Time-dependent X-ray reflectivity during cyclic voltammetry reveals an unexpected hysteresis in the EDL structure during polarization switching, suggesting an energy penalty for EDL reconfiguration. These experimental results will be connected to analytical models and molecular dynamics simulations. This work brings new molecular-level insight to the potential dependence in the static and dynamic EDL structure.