Leveraging C2H4N3+CH3SO3– Ionic Liquid-Embedded MOF-808 and Biobased Vitamin E for Enhanced Performance and Oxidative Tolerance in Zero-Humidified PEMFCs

Abstract

Integration of diverse functional materials offers a multifaceted approach to tackle the challenges of developing highly conductive, durable, and cost-effective membrane electrolytes for energy applications. A simple, low cost protic ionic liquid (PIL) “triazolium methanesulfonate” (C₂H₄N₃⁺CH₃SO₃^–) was entrapped into the pores of zirconium-based metal–organic framework (MOF), MOF 808 (Zr₆O₄(OH)₄(BTC)₂(HCOO)₅(H2O)₁(OH)₁) to develop a hybrid proton conductor (TrzIL@M). This generated a new class of material that can harness the intrinsic properties of rigid host-soft guest, resulting in synergistic interplay that forms ordered, long-range ion conducting ducts and prevents PIL leaching when incorporated in a polymer matrix. Further, electrolytes are susceptible to degradation by reactive oxygen species. To combat this, we drew inspiration from biological systems and utilized the renewable antioxidant vitamin E (α-tocopherol) as a potent radical scavenger. Finally, a mixed matrix membrane electrolyte was developed by incorporating TrzIL@M and vitamin E into a SPEEK matrix. The resulting membrane (SP/TrzIL@ME) exhibited a high conductivity of 0.035 S/cm at 100 °C ∼2.7 times upsurge in comparison to pristine SPEEK membrane, while PIL loss was reduced by 18%. SP/TrzIL@ME achieved maximum current density of 1327 mA/cm² and peak power density 245 mW/cm² in zero-humidified conditions. SP/TrzIL@ME operated effectively in nonhumidified state mitigating flooding, swelling, and dimensional distortion associated with humidity-dependent membranes. Notably, the membrane could retain 91% of open-circuit voltage after five cycles (50 h) durability testing attributed to the scavenging activity and recyclability of vitamin E, establishing the PEM as a potential candidate for proton exchange membrane fuel cells.