Sulfonated resorcinol-formaldehyde polymer gels synthesized in Nafion ion clusters as nanoscale reactors for a filler of hybrid proton exchange membranes

Nafion ion clusters are used as nanoscale polymerization reactors to synthesize sulfonated resorcinol-formaldehyde (RF) polymer gels to be used as fillers of a hybrid membrane. Because these ion clusters are distributed well over the entire Nafion structure, the polymer gels are also well dispersed in this unique organic–organic hybrid membrane compared with inorganic–organic hybrid membranes prepared by common recasting process that usually show serious aggregation of the fillers. The obtained organic–organic hybrid membranes show increased water uptake capability and the higher proton conductivity relative to pristine Nafion membrane under low-humidity conditions. In single-cell proton exchange membrane fuel cell operation without external humidifying system, the maximum power density of 289 mW/cm2 is observed for the membrane electrode assembly (MEA) fabricated with 2 wt% sulfonated RF polymer gels/Nafion hybrid membrane, which is ca. 63% higher than that of the MEA fabricated with pristine Nafion membrane. However, pristine Nafion membrane showed similar or better performance to that of hybrid membranes when reactant gases are fully humidified.