Composite membranes have been prepared by impregnation of Nafion into the expanded polytetrafluoroethylene (EPTFE) matrix. Nafion loading in the composite membranes was kept constant at 2？mg/cm2. The lower amount of electrolyte per unit area in the composite membranes offers cost advantages compared to conventional membrane of 50？μm thickness with an electrolyte loading of ~9？mg/cm2. Composite membranes (30？μm thickness) were found to have higher thermal stability and mechanical strength compared to the conventional membranes (50？μm thickness). The performance of the membrane electrode assembly made with these composite membranes was comparable to that of the conventional membranes. Single cells fabricated from these MEAs were tested for their performance and durability before scaling them up for large area. The performance of a 20-cell stack of active area 330？cm2 fabricated using these membranes is reported. 1. Introduction Polymer electrolyte membrane fuel cell (PEMFC) presents an attractive alternative to traditional power sources, due to high efficiency and low pollution. The efficiency of the fuel cell vehicle using direct hydrogen fuel cells has been reported to be twice that of the gasoline vehicles [1, 2]. Fuel cell efficiency is high even at partial loads compared to the internal combustion engines, which operate at high efficiency only at full loads. The only emissions in vehicles operating on hydrogen as fuel is water and is hence nonpolluting. Fuel cell stacks of sub-kW and 1？kW level find applications as power sources in electronic equipments and as power source in portable applications. A 3？kW fuel cell stack has been projected for applications in the telecommunication sectors as highly reliable and durable on-site power generation technology is required for these applications. Stacks of 5？kW and above are used as power sources in various stationary and vehicular applications. Combined heat and power generation using fuel cells is especially attractive for stationary power generation. Further, these short stacks hybridized with electrical storage devices (batteries and/or ultra-capacitors) can have several benefits, including capturing regenerative braking energy, enhancing fuel economy, providing a more flexible operating strategy, overcoming fuel cell cold-start and transient shortfalls, and lowering the cost per unit power. In a PEMFC, the proton-conducting membrane is located between the cathode and anode and transports protons from anode to cathode. The membranes for high performance PEM fuel cells have to meet the requirements of
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