(295a) Catalyst Degradation in Phosphoric Acid Fuel Cells

UTC Power has installed 260 stationary phosphoric acid fuel cell (PAFC) power plants for customers in 19 countries on five continents. These power plants have accumulated over 8 million hours of field operation, with the fleet leading stack exceeding 62,000 hours of operation. The current power plants are designed with a 5 year stack lifetime, and we are currently developing a next generation PAFC stack with a 10 year operating life¹.

As part of this development activity, we investigated the catalyst degradation of PAFC stacks which operated in commercial service for excess of 40,000 hours. The catalyst was characterized through performance measurements, electrochemical surface area measurements, and microscopic analysis. As expected, surface area reduction was observed due to agglomeration of the catalyst particles on both the anode and cathode. This surface area loss on the cathode accounted for the majority of the fuel cell performance loss over time. A temperature dependence on surface area reduction was developed by analyzing samples from different areas of operation within the stack at different temperatures. The resulting data was fit to a traditional catalyst agglomeration model² to provide insight into the mechanism and provide means for predicting decay of PAFC stacks under different operating temperatures and durations.

References

¹ UTC Power (March 29, 2007). UTC Power fuel cell fleet attains 8 million hours of operation. Press release.

² Ruckenstein E., and B. Pulvermacher, ?Kinetics of Crystallite Sintering During Heat Treatment of Supported Metal Catalysts?, AIChE Journal, 19, 356 (1973).