An ionic liquid-mediated hydrogen-bond network: a pathway to high-efficiency PEMFCs with unlocked active sites of Pt/C catalysts

The strong adsorption of ionomer sulfonate groups (-SO₃⁻) onto platinum (Pt) nanoparticles significantly hinders the catalytic activity and mass transport at the Pt/ionomer interface, compromising electrode reaction efficiency in proton exchange membrane fuel cells (PEMFCs). Herein, we reconstruct a hydrogen-bond network using a hydroxyl-functionalized three-dimensional structured ionic liquid (IL) to effectively mitigate ionomer poisoning while unlocking additional active sites of Pt/C catalyst-based membrane electrode assemblies (MEAs). A triple-promotion mechanism is proposed: enhancing proton conductivity through an extended hydrogen-bond network, improving local oxygen transport via reducing ionomer density on the Pt surface through hydrogen bonding interactions between the IL and -SO₃⁻, and boosting catalytic activity by upshifting the d-band center and weakening the Pt-O bond. This mechanism is rigorously verified through in situ and ex situ characterization, molecular dynamics simulations, and density functional theory calculations. As a result, MEAs integrated with an IL-modified Pt/C catalyst (IL-Pt/C) exhibit a 1.0-fold increase in mass activity (0.220 vs. 0.112 A mg_Pt⁻¹), a 47.3% reduction in pressure-independent resistance (0.10 vs. 0.19 s cm⁻¹), and a 36% decrease in proton conductivity resistance (0.096 vs. 0.150 Ω cm²), achieving a notable peak power density of 1.54 W cm⁻² (H₂/air). This IL modification strategy presents a rational approach for optimizing the Pt/ionomer interface and improving PEMFC performance.