National Research Council of Canada. NRC Institute for Fuel Cell Innovation
A new class of proton-conducting hybrid membranes have been developed using a combination of a solvent-directed infiltration method and sol−gel chemistry with a range of organofunctional silane and phosphate precursors. The phase-separated morphology of Nafion is used as a structure-directing template, which drives the inorganic component into the ionic clusters of the Nafion membrane. The kinetics of the sol−gel reactions were monitored using spectroscopic techniques. Photoacoustic Fourier transform infrared spectroscopy (PA-FTIR) confirms formation of Si−O−Si and Si−O−P bridges in the hybrid membranes, indicating silicate and phosphosilicate structures. The presence of the silicate/phosphosilicate network in the hybrid membranes enhances their thermal stability, thermomechanical properties, water retention at elevated temperatures, and relaxation temperature Tc. Scanning electron microscopy (SEM) and small angle neutron scattering were used to determine the morphology and microstructure of these membranes. A structural model of the hybrids is proposed to describe the size and shape of the inorganic particles, which is consistent with the SEM observations. Proton conductivity measurements were made from 30 to 80 °C and at relative humidities ranging from 30% to 90%. The presence of inorganics in the polymer membrane has improved the water management in these new organic−inorganic hybrids at elevated temperatures above 100 °C, which is a key parameter when designing proton-exchange membranes for medium-temperature fuel cell application.