Programmable Solid‐Electrolyte Interfaces for Efficient and Selective Electrochemical Hydrogenations

Electrode binders, typically regarded as passive mechanical additives, in fact define a solid-liquid interface that governs charge screening and local proton-electron transfer kinetics. Here we show that fluorine-free poly(ionic liquid)s (PILs) operate as solid-state electrolyte layers whose intrinsic electric fields modulate the competition between electrochemical hydrogenation (ECH) and the hydrogen evolution reaction (HER). When applied to Pd-C catalysts, PIL binders reshape the electric double layer by repelling alkali cations and modulating interfacial pH, which change the kinetics of proton-electron transfer, suppress Tafel hydrogen recombination and promotes selective coupling of adsorbed hydrogen with organic substrates. The resulting electrodes achieve up to fivefold higher ECH yields and fourfold greater Faradaic efficiencies than those based on Nafion or PVDF in three different pH values 0.6, 5.2, and 13, while simultaneously reducing Pd leaching. These findings identify the polymer additives more than a binder, but rather as an active field-modulating medium. A solid analogue of the electrolyte double layer, thus extending classical electrolyte-effect concepts to polymer-confined interfaces and offering a strategy for binder-controlled interfacial design in electrosynthetic systems.