Alkyl Chain Dependent Imidazolium Ionic Liquid Modification of PtC Regulates Interfacial Water Networks for Enhanced Oxygen Reduction

Abstract

Modulating the structure of interfacial electric double layer (EDL) represents a pivotal strategy for enhancing the oxygen reduction reaction activity (ORR) of PtC catalysts in acidic media. This work elucidates the mechanistic influence of imidazolium based ionic liquids (IL) with tailored alkyl chain lengths (C₂, C₄, C₆) on both the ORR performance and the nanoscale organization of the EDL at the Pt electrocatalyst interface. We demonstrate that the imidazolium ring coordinates selectively with Pt surfaces, enabling stable adsorption and creating a well ordered, nanoconfined environment. Increasing alkyl chain length enhances hydrophobic interactions, which systematically disrupt the interfacial water network and break hydrogen bond continuity. Remarkably, the [C₄C₁im]⁺ cation exhibits an optimal balance for structuring hydrogen bonds across both confined and bulk like regions, facilitating dynamic water clusters that yield maximum ORR activity. Through combined in situ attenuated total reflection surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) and electrochemical studies, we uncover how molecular level design of IL governs hydrogen bond dynamics and directs proton coupled electron transfer kinetics, offering profound insights into interfacial microengineering for advanced electrocatalysis.