Metal dioxide supported heteropolyacid/Nafion® composite membranes for elevated temperature/low relative humidity PEFC operation

Organic/inorganic composite membranes with different inorganic heteropolyacid (HPA) additives maintain sufficient proton conductivities for elevated temperature (>100 °C) low relative humidity (<50%) operation. However, membrane and membrane electrode assembly (MEA) processing is severely curtailed because of the solubility of the HPA additives in aqueous media. Composite membranes with the HPA additive supported on metal dioxide frameworks were investigated in this work. Supporting the HPA on commercial supports proved to be inadequate to stabilize the additive. Superior stabilization, as demonstrated by IR spectroscopy, was achieved over a range of membrane compositions by using an in situ sol–gel approach using metal alkoxide precursors. The membranes were robust, and demonstrated low H2 crossover currents of 0.7 mA/cm2 for a 25 μm thick membrane. The decomposit ion onset temperature of the composite membrane was extended by 30 °C over Nafion®. Membrane electrode assemblies prepared using the stabilized composite membranes were evaluated at high temperatures and low relative humidities in an operating fuel cell. The conductivities of the composite membranes at 120 °C and 35% relative humidity were on the order of 1.6 × 10−2 S/cm.