(589a) Probing the Electrical Double Layer in Highly-Concentrated Salt Environments

The electrical double layer (EDL) manifests at every charged solid-liquid interface. The ion distribution away from the surface, known as the decay length, directly impacts the double-layer capacitance of the interface. Additionally, this ion distribution controls the reactivity of the interface, impacting both inner and outer-sphere electron transfer reactions. Recently, it has been discovered that highly-concentrated salts in water have surprising electrochemical stability windows much larger than would be expected from thermodynamics; one hypothesis is that salt structure at the electrode interface within the EDL suppresses the water-splitting reaction. Understanding the relationship between EDL structure and electrochemical performance is key to unraveling why these electrolytes exhibit this unexpected behavior, and how to apply these properties to other systems for enhanced electrolyte engineering. Here, we use an electrochemical surface forces apparatus (ESFA) to measure oscillatory structural forces and electrostatic decay within the EDL, to investigate the salt layer structure and decay length, respectively. We measure these properties for various salt concentrations of both mono- and divalent salts, at a variety of different potentials. In this way, we correlate electrochemical performance with experimentally-revealed structural signatures of the EDL.