SBIR-STTR Award

The fuel cell power supplies of today are two times too heavy compared to man-portable power supplies. A major portion of the weight is in the fuel cell stack, a stack of carbon electrodes with metal bipolar plate separators that are sandwiched between two end plates and held in place by tie rods. We continue to investigate lighter weight materials to use in our conventional fuel cell stack. However, in this effort we propose to investigate an innovative design, the strip cell stack, that completely eliminates the bipolar plates, end plates and tie rods. The strip stack is 4.6 times lighter than a bipolar fuel cell stack. In a conventional Proton Exchange Membrane (PEM) fuel cell stack, electrons and protons are conducted perpendicular to the electrode plane. In the strip cell design, ionic conduction is perpendicular to the plane of the electrodes while electron flow is in the plane of the electrodes. Phase I will demonstrate the feasibility of the design with a 4 cell "substack." In Phase II we will build a coiled 300 watt cell "stack." The coiled strip cell stack is formed from a sheet of planar strip cells rolled together and placed inside a thin lightweight plastic tube. The 300 watt strip cell stack should fit in a tube which is about 8.9 cm. in diameter and 20.3 cm. long. The total weight should be slightly over 1 Kg.

Development of an extremely lightweight innovative strip design fuel cell stack began in Phase I. The design eliminates bipolar plates, end plates, and tie rods, some of the heaviest components in a conventional fuel cell stack. In an un-optimized four cell stack we demonstrated .21 watts per gram of stack weight. Strip stack material will cost half as much as a conventional bipolar fuel cell stack. In Phase II we will develop fuel cell stacks made from coiled sheets of planar strip cells. The 150 watt, 24 volt fuel cell stack will weigh 3 pounds and produce .7 volts/cell at 50 ASF. The 50 watt, 6 volt fuel cell stack will weigh 1.7 pounds and produce .7 volts/cell at 50 ASF. Four fuel cell stacks will be delivered.

Benefits:
An extremely lightweight fuel cell will provide portable power for the Army. In the planar configuration, the small light weight strip design is an attractive alternative to currently available computer batteries. Texas Instruments has expressed an interest in pursuing this with Analytic Power. In higher power applications, the compact coiled design would replace thermoelectric generators or batteries used to power remote sites. There are many medical applications that would also benefit from a lightweight compact fuel cell power supply