GEI HIGH TEMPERATURE PEM MEMBRANES AND FUEL CELL STACKS
GEI fuel cell stacks employ high temperature PEM fuel cell membrane assemblies operating at 160C-180C rather than low temperature PEM membranes that traditionally operate at 70C-80C. Our membrane assemblies (MEA), supplied by BASF, are integrated into our proprietary fuel cells stack design and are denoted as the Celtec®-P 1000 MEA. Celtec®-P MEAs are based on the high temperature resistant polymer polybenzimidazole (PBI) acid electrolyte. Today, although PBI is mainly used for fire protection fabrics, Celtec®-P MEA is the basis for a new generation of high temperature PEM fuel cells which are more cost-effective, efficient and reliable than conventional low temperature fuel cell systems with the following features:
• Operation at temperatures between 120 and 180 °C
• No water management necessary
• High tolerance of CO (Carbon Monoxide)
• High tolerance of H2S (Hydrogen Sulfide)
• Excellent long-term stability
• Operational robustness
More performance and durability information regarding the high temperature BASF MEA can be located at: http://www2.pemeas.de/home.asp. Due to the HT-PEM high tolerance to CO and H2S, fuel processing of liquid carbon based fuels become very cost effective. It has been shown that low temperature fuel cells require CO concentrations less than 0.001% or 10 PPM (parts per million), while high temperature fuel cells are more tolerate, i.e. 3%-5% or 50,000 PPM. Additionally, low temperature PEM fuel cells require H2S concentrations less than 100 PPB (parts per billion) while high temperature fuel cells require H2S concentrations less than 10 PPM or 100 times more tolerate.
DOE Durability Targets
Additionally, BASF membrane durability testing (www2.pemeas.de) confirms a low degradation rate of 6.0x10-6 Volts/Hr per cell after 18,000 hours operating on pure H2 (or decrease in fuel cell stack efficiency of 20%). Assuming a beginning-of-life cell stack efficiency of 60%, the predicted end-of-life stack efficiency is 40% for a 2kW 24 cell stack after 40,000 hours of operation. While this preliminary "rough" scenario would seem to meet the DOE project objective, predicted operation with reformed fuels will be lower by approximately 5%. However, GEI is working with supplier BASF to evaluate its latest membrane development, i.e. CELTEC P-2000, which has improved transient performance for start/stop operations and improved long-term high temperature durability. The expected fuel cell efficiency degradation over 40,000 hours is 10% or implying a beginning of life efficiency requirement of 50% to meet the DOE end of life target of 40%.
GEI Balance-of-Plant and Integrated Controls
In addition to fuel impurity tolerance, high temperature PEM (HT-PEM) fuel cell membranes do not require humidity of inlet gases as for low temperature (LT-PEM) fuel cells. As such, the overall "system" efficiency is higher with fewer components and simpler controls and more reliable operations. The GEI power system couples both the reformer and high temperature fuel cell stack into an integrated unit. The excess fuel cell stack coolant heat is used to pre-heat the water for the steam reformer, and the stack cathodeair inlet. The unused hydrogen and anodeexhaust CO and CO2 is burned within a tail gas burner and supplies heat for the reformer which reduces the diesel fuel required within the reformer to maintain the catalysts bed temperature. Finally, the anode exhaust water is condensed and used within the reformer to minimize the external make-up water required. This integrated infrastructure design leverages the high-gradeheat attributes of high-temperature PEM fuel cell stacks. As such the overall system is cost effective, compact, thermally efficient and provides high grade heat for combined heat and power applications.
GEI High-Temperature World Fuel Cell Stack
GEI'spatented high temperature fuel cell stack design has flow field channel designs optimized for reformed fuels and incorporates a robust manifold design scalable from 2kw-10kw. This allows a single design for a wide of range of power requirements without re-occurring engineering design cost and provides the scalability necessary for large volume commercialization to reduce manufacturing cost.
Below are IV curves for GEI's 500W HT-PEM fuel cell stack operating on a mixture of 2% and 5% CO/H2 fuel to simulate performance on reformed fuels. Note when operating on 2% CO there is a 4% reduction in stack power at 200 ma/cm2 @ 160C, and a 9% reduction in stack power at 400 ma/cm2. The 2% CO is the confirmed maximum reformer operating characteristics on a dry mass basis. However, the HT-PEM power reduction is off-set by requiring fewer components and a higher "system" efficiency as compared to LT-PEM fuel cell systems.