(278b) Water Management by Materials Design and Engineering of the Membrane and Electrode Assemblies

Abstract

      In a Polymer Electrolyte Membrane fuel cell (PEMFC), water is needed to keep the polymer electrolyte (membrane/ionic phase in the catalyst layers) hydrated to maintain high ionic conductivity. Too little water results in dehydration and high ionic resistance, and too much water results in flooding of the electrode components (catalyst and gas diffusion layers). Both cases lead to poor fuel cell performance. Furthermore, recent works have shown that the degradation rate of the membrane and electrode assembly in a PEM fuel cell could be reduced significantly if the fuel cell operated in a near liquid-water saturated condition. Consequently, a PEMFC depends on proper water management to obtain high power density, energy efficiency and durability.

      Traditionally, water management has been addressed by system design and engineering. That is, by adding auxiliary systems to the basic fuel cell system to provide humidification to the anode and to remove water from the cathode. This approach adds significant complexities and costs and reduces the overall efficiency of the PEMFC system. Development of new materials and a better understanding of the functions of these materials^1,2,3 have led to paradigm shift as to how water management can be implemented in a PEMFC system. Theoretical calculations shown in Table I for the configurations shown in Figure 1 illustrate that if materials with the right properties are used in the membrane and electrode assemblies such that the water transported across the membrane by electro-osmosis could be forced back to the anode to achieve zero net water transport across the membrane, then water management in a PEMFC system could be attained with no external-water requirement. If this objective could be achieved, the PEM fuel cell system and its operation would be greatly simplified, and its cost would be greatly reduced, thus helping to accelerate the commercialization of this technology.

      This presentation will discuss the overall approach to achieve water management with no external water requirements and the experiments used to measure and evaluate materials that will help us attain zero net water transport across the membrane.

References

1.      A. Weber and J. Newman, J. Electrochem. Society, 152, A677-A688 (2005).

2.      U. Pasaogullari, C.Y. Wang, and K.S. Chen, J. Electrochem. Society, 152, A1574-A1582 (2005).

3.      R. Jain and T. Nguyen, "Modeling the Effect of Microporous Layer in PEM Fuel Cells," Proton Exchange Membrane Fuel Cells V,? Electrochemical Society 2005 Annual Meeting, Paper No. 996, Los Angeles, CA, Oct. 16-21, 2005.

Table I.  Water management calculated results for the cases shown in Figure 1

Figure 1. System configurations for various water management approaches: [1] no H₂ recirculation and no cathode water recovery, [2] with H₂ recirculation, [3] with cathode water recovery.