Superacidity in Nafion/MOF Hybrid Membranes Retains Water at Low Humidity to Enhance Proton Conduction for Fuel Cells.

A hybrid membrane of superacid sulfated Zr-MOF (SZM) and Nafion shows much superior performance to Nafion, particularly for fuel cell operating under low humidity. The Brønsted acidic sites in SZM networks retain an ample amount of water which facilitated proton conduction under low humidity. The water retention properties of Nafion-SZM hybrid membranes with 1 wt % loading of SZM increased at 35% relative humidity and outperformed commercial unfilled Nafion membrane. The proton conductivity increases by 23% for Nafion-SZM hybrid compared to unfilled Nafion membrane. The Nafion-SZM membrane also shows higher performance stability at 35% relative humidity than Nafion, as confirmed by close monitoring of the change of open circuit voltage for 24 h.