Evaluation of Proton Exchange Membrane Reinforced with Fluoroplastic Fiber Sheet for Fuel Cell

Abstract

Ion exchange membranes for fuel cell are expected to become thinner in order to reduce the membrane resistance. On the other hand, a thinner membrane has a weaker mechanical strength. The novel proton-exchange membranes were prepared by reinforcing with two kinds of 100 % PTFE fiber sheets, which were fabricated by a papermaking method with or without uniaxially stretching as the core for a reinforced membrane. The stress, the strain, water content, ion exchange capacity and ionic conductivity were measured for different membranes. By pre-treating the PTFE sheet at 320 degree and hot-pressing the membrane at 140 degree, a strength of 27 MPa was obtained for the membrane reinforced with a PTFE sheet in the machine direction (MD) and 21 MPa in the transverse direction (TD). The tensile yield stress was almost the same as that of Nafion112 in both directions. The water content and proton conductivity of the membrane reinforced with the PTFE sheet decreased to less than 28.3 % and 20 % when compared to that of Nafion112, respectively. The obtained ion exchange capacity was 0.89 mol/kg-dry.