Performance of a High Temperature Polymer Electrolyte Membrane Fuel Cell with Low Catalyst Loading Produced by Reactive Spray Deposition Technology

Traditional polymer electrolyte membrane fuel cells (PEMFCs) typically operate at temperatures around 80 °C. As a result of these low operating temperatures PEMFCs suffer from several performance issues such as problems with water and thermal management, poor electrochemical kinetics, and intolerance to poisons such as carbon monoxide. If the temperature can be increased to upwards of 200 °C the kinetics for the sluggish oxygen reduction reaction can be greatly improved and upwards of 1% carbon monoxide in the feed gas stream will not deteriorate cell performance. Additionally, water in the cell will exist primarily in the vapor phase helping mitigate the flooding of the electrodes. Finally, the greater discrepancy between the cell temperature and the surrounding environment enhances heat rejection and simplifies thermal management [1].

In the current work, gas diffusion electrodes (GDE) for a high temperature PEMFC are fabricated via Reactive Spray Deposition Technology (RSDT) [2,3]. This flame based deposition technique produces Pt nanoparticles through combustion of a precursor solution consisting of a metal organic compound (platinum(II) acetylacetonate) dissolved in a high enthalpy solvent (a mixture of xylene, acetone, and propane). The Pt catalyst is attached to a carbon support, Vulcan XC-72R in this case. This is accomplished by spraying a carbon based slurry, containing a PTFE binder, through secondary nozzles into the path of the Pt nanoparticles in the post luminous zone of the flame. In order to produce the GDE (5×5cm), the resulting spray from the RSDT process is directed at a gas diffusion layer substrate (SIGRACET^® GDL25BC, 5×5cm). The resulting GDEs were then hot pressed to an ADVENT^® membrane doped with 85wt% phosphoric acid to produce the 5×5cm single cell.

A study of the effect of the binder to carbon ratio (PTFE/Vulcan XC-72R) on cell performance and structure was performed through the use of polarization scans, cyclic voltammetry, mercury porosimetry, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). PTFE/Vulcan XC-72R ratios ranging from 0.1 to 1 were studied. It was determined experimentally that the best performance resulted from a binder to carbon ratio of 0.9. This is believed to be due to the well-developed Pt nanoparticle distribution, small pores and uniform pore size distributions, and high electrochemical surface area. These experimental results will be coupled with a semi empirical model to mimic cell performance based on the catalyst agglomerate concept [4]. An attempt will be made to link the physical characteristics of the RSDT produced GDE to the appropriate parameters of the model to develop a firm understanding of the influence of the RSDT process parameters on catalyst structure and performance.

References

[1] J. Zhang, Z. Xie, J. Zhang, Y. Tang, C. Song, T. Navessin, Z. Shi, D. Song, H. Wang, and D. P. Wilkinson, J. Power Sources, 160, 872 (2006).

[2] R. Maric, J. Roller, and R. Neagu, J. Therm. Spray Technol., 20, 696 (2011).

[3] J. Roller, R. Neagu, F. Orfino, and R. Maric, J. Mater. Sci., 47, 4604 (2012).

[4] K. Scott and M. Mamlouk, Int. J. Hydrogen. Energ., 34, 9195 (2009).

Acknowledgements

The authors would like to gratefully acknowledge financial support provided by the National Science Foundation. Advents Technology Inc. is also gratefully acknowledged for supplying the membranes used in this study.