New nanocomposite proton conducting membranes based on a core–shell nanofiller for low relative humidity fuel cells

Abstract

New hybrid inorganic–organic proton conducting membranes containing a ZrTa nanofiller dispersed in a Nafion^® matrix are described. The ZrTa nanofiller exhibits a “core–shell” morphology, where the harder ZrO₂ forms the “core”, which is covered by a “shell” of the softer Ta₂O₅. The hybrid membranes are thermally stable up to 170 °C. Interactions between the polymer matrix and the nanofiller increase the thermal stability of both the –SO₃H groups and the fluorocarbon polymer backbone. In comparison with Nafion, the hybrid membranes have a lower water uptake (W.U.) that depends on the concentration of nanofiller. The residual water, which is approximately 4 wt%, is likely located at the Nafion–nanofiller interface. Infrared results indicate that the nanofiller does not neutralize all of the R–SO₃H groups in the hybrid membrane and the small amount of residual water in the material does not cause the dissociation of the R–SO₃H protons. Fuel cell tests show that the maximum power density yielded by the membrane electrode assembly (MEA) containing the hybrid membrane is better than that of the MEA containing Nafion, particularly at low values of relative humidity. The hybrid membranes require much less water to conduct protons effectively and are more efficient at retaining water than Nafion at low water activities.