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

Acidic electrocatalytic CO 2 reduction (eCO 2 R) 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 eCO 2 R. 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 (FE CO ) 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 FE CO above 90% in strongly acidic and low-potassium electrolyte (pH = 1, C K + = 0.05 M).