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

ABSTRACT 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‐NH ₂ and sulfonated graphitic carbon nitride (sgC ₃ N ₄ ) 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‐NH ₂ : sgC ₃ N ₄ = 1:1, 1% w/w) exhibited high ion exchange capacity and proton conductivity (K ^m = 27.1 mS cm ⁻¹ at 80°C), 2.65 times higher than pristine PDS. Its low VO ²⁺ permeability and high ion selectivity arise from synergistic acid‐base and H‐bonding interactions between ‐NH/‐NH ₂ and ‐SO ₃ H groups, complemented by non‐covalent interactions and physical blocking within the membrane matrix. The porous UiO‐66‐NH ₂ and layered sgC ₃ N ₄ 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).