Molecularly Engineered Polystyrene-Imidazolium Polyelectrolytes for CO ₂ Electrolysis in Strongly Acidic Media

Acidic electrocatalytic CO2 reduction (eCO2R) holds promise for mitigating carbonate loss, yet selectivity and stability challenges persist due to competing hydrogen evolution reactions (HER) and severe salt precipitation associated with high-concentration alkali cation electrolytes. This work presents a molecularly engineered polystyrene-imidazolium (POM) polyelectrolyte with precisely tailored imidazolium/octadecylamine stoichiometries for acidic eCO2R. Optimized POM-0.7 exhibits high ion exchange capacity (2.18 mequiv g–1) with a low water uptake (25.8%), enabling NiNC/POM-0.7 to achieve 89% CO Faradaic efficiency (FECO) at 50 mA cm–2 in a flow cell fed with pure acid (pH = 2). Further integrating NiNC/POM-0.7 with an electrospun POM/PVDF in membrane electrode assemblies (MEAs) enables near-unity CO selectivity at 100–400 mA cm–2, with a maximum CO partial current density of 411 mA cm–2 and stable operation over 150 h with an FECO above 90% in strongly acidic and low-potassium electrolyte (pH = 1, CK+ = 0.05 M).