Development and characterization of novel composite membranes for fuel cell applications

In this paper, we report a novel composite electrolyte membrane consisting of a polyethylene substrate and a Nafion ionomer. Polymer Electrolyte Membranes (PEMs) have been gaining increasing attention in the fuel cell industry due to their excellent proton conductivity and among them the Nafion membrane is by far the most widely used membrane electrolyte. However, it suffers from several drawbacks such as high fuel crossover and low mechanical strength, which lower the fuel cell performance and disturb the structural integrity. In order to deal with these problems, we have prepared a pore filling membrane that is composed of a porous substrate and a filling electrolyte. Nafion was used as a filling electrolyte and was impregnated into the pores of the porous substrate made up of ultra-high molecular weight polyethylene (UHMWPE). The UHMWPE backbone serves as a structural support and blocks the fuel crossover while the impregnated Nafion molecules provide the proton conducting path. A porous UHMWPE membrane with a porosity of approximately 66% was prepared, and the Nafion electrolyte was impregnated into the pores so that an NPE (Nafion-polyethylene composite) membrane was formed. Major accomplishments of this work are (a) the membrane is biaxially oriented and has higher tensile strength and modulus especially under wet conditions as well as better electrolyte conductivity because the resistivity in the system is reduced due to the development of a very thin (13 mm) film composite, and (b) the electrolytic membrane is economical because of the utilization of a lesser amount of ionomer. Systematic characterization of both porous polyethylene and the NPE composite has been performed using SEM, EDAX, XRD, XRF, porosity measurement, tensile tests, proton conductivity, and fuel cell performance tests.