Sulfonated Graphitic Carbon Nitride/UiO‐66‐NH ₂ Infused PVDF‐ co ‐HFP‐Tailored Zwitterionic Membranes for Low‐Humidity Hydrogen Fuel Cells and Vanadium Flow Batteries

A "two-birds-one-stone" strategy was employed to design a multifunctional membrane capable for both energy production and storage devices. Poly(vinylidene fluoride-co-hexafluoropropylene)-g-poly-2-(dimethylamino)ethyl methacrylate-based zwitterionic composite membranes were synthesized via ATRP-mediated grafting, followed by N-alkylation with 1,3-propanesultone. The membrane architecture was further tailored by incorporating UiO-66-NH₂ and sulfonated graphitic carbon nitride (sgC₃N₄) as complexed fillers, forming a hierarchically organized ionic framework that reconciles the trade-off between ionic conductivity and fuel/electrolyte permeability. The optimized PDS-11 membrane (UiO-66-NH₂: sgC₃N₄ = 1:1, 1% w/w) exhibited high ion exchange capacity and proton conductivity (Km = 27.1 mS cm⁻¹ at 80°C), 2.65 times higher than pristine PDS. Its low VO²⁺ permeability and high ion selectivity arise from synergistic acid-base and H-bonding interactions between -NH/-NH₂ and -SO₃H groups, complemented by non-covalent interactions and physical blocking within the membrane matrix. The porous UiO-66-NH₂ and layered sgC₃N₄ improved water retention and structural robustness, yielding 89% power retention at 70% RH in PEMFCs, with a mere OCV decay rate of 1.6 mV h⁻¹ over 50 h. PDS-11 also exhibited exceptional VRFB performance with CE, VE, and EE of 97.41%, 76.32%, and 74.34%, respectively,, over 200 cycles at 120 mA cm⁻² (42.3% of capacity retention after 100 cycles with 620 min of OCV retention).