Hydrogen-bond-networks control redox-coupled reactivity in ionic liquid electrolytes

Controlling the fate of electrogenerated intermediates is central to achieving selective and reversible electrochemical processes in complex media. Although catalysts and electrode materials are routinely used to direct the fate of these intermediates, the electrolyte-despite its significant role in determining the electrochemical process's outcome-remains underexploited. In practice, electrolyte design remains primarily guided by bulk transport properties, such as viscosity and ionic conductivity, which mostly fail to capture the molecular-level interactions that determine intermediate fate. Here, we investigate a compositionally tunable choline-geranate-geranic acid ionic liquid (IL) electrolyte platform to determine how hydrogen-bond network organization regulates electrochemical behavior. Varying the geranic acid content reorganizes the hydrogen-bond network, as evidenced by infrared spectroscopy and variable-temperature ¹H NMR, while preserving ionic character. Using the ferrocene/ferrocenium redox couple as a diagnostic probe, cyclic voltammetry reveals a transition from irreversible to near-reversible behavior with increasing geranic acid content, despite increasing viscosity and non-monotonic conductivity trends. Cyclic voltammetry, rotating-disk electrode, and variable-temperature measurements indicate that the irreversibility at low geranic acid content arises from a kinetically coupled chemical process rather than from transport limitations. Time-resolved UV-vis spectroelectrochemistry shows that ferrocenium is rapidly consumed in carboxylate-dominated environments but persists in hydrogen-bond-rich media, with protic cosolvents further suppressing redox-coupled reactivity. These results demonstrate that, within this IL series, electrochemical behavior is governed by the local solvation environment and its control over intermediate reactivity rather than bulk transport properties alone. This work establishes the electrolyte structure as a tunable handle for regulating the fate of electrogenerated intermediates, providing a structure-centric design strategy for ILs, deep eutectic solvents, and hybrid electrolytes.