1420
Imaging Phosphoric Acid Migration in High Temperature Polymer Electrolyte Fuel Cells by X-Ray Tomographic Microscopy
Tuesday, October 13, 2015: 17:20
212-C (Phoenix Convention Center)
S. H. Eberhardt (Electrochemistry Laboratory, Paul Scherrer Institut), F. Marone (Paul Scherrer Institut), M. Stampanoni (Swiss Light Source, Paul Scherrer Institut, Institut of Biomedical Engineering, ETH Zürich), F. N. Büchi (Electrochemistry Laboratory, Paul Scherrer Institut), and T. J. Schmidt (Laboratory of Physical Chemistry, ETH Zürich, Electrochemistry Laboratory, Paul Scherrer Institute)
High temperature polymer electrolyte fuel cells (HT-PEFC) use phosphoric acid (PA) as the proton conducting electrolyte, which is imbibed in a polybenzimidazole (PBI) membrane. The low vapour pressure of PA allows for increased operating temperatures of up to 200°C. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels up to 3% and H
2S up to 10 ppm can be achieved.
1 Phosphoric acid doped PBI membranes are therefore ideal candidates for cost-efficient combined heat and power (CHP) as well as hydrogen separation, purification and pumping applications. Unlike low temperature sulfonic acid based PEFC, the electrolyte is not covalently bound to the polymer backbone of the membrane and migration of anions in the electric field can occur similar to what has been observed in phosphoric acid fuel cells (PAFC).
2,3 We have recently demonstrated how X-ray tomographic microscopy (XTM) can be applied for imaging electrolyte migration in HT-PEFC under dynamic operation.
4 It was shown, for the first time, that PBI based membrane systems exhibit extensive PA migration from cathode to anode under high current operation. PA flooding of the anode gas diffusion layer (GLD) and flow field channel was observed.
In this contribution, the application of synchrotron based XTM for in-operando imaging and quantification of migrated phosphoric acid in HT-PEFC will be presented. The influence of current density, temperature, membrane material (conventional m-PBI film casted5 and sol-gel based6 membranes) and phosphoric acid loading will be discussed.
[1] T. J. Schmidt and J. Baurmeister, ECS Trans., 3, 861–869 (2006).
[2] H. R. Kunz, ECS Trans., 11, 1447–1460 (2007).
[3] H. R. Kunz, Electrochem. Soc. Proc., 99-14, 191–207 (1999).
[4] S. H. Eberhardt, M. Toulec, F. Marone, M. Stampanoni, F. N. Büchi, and T. J. Schmidt, J. Electrochem. Soc., 162, F310–F316 (2015).
[5] R. Savinell, E. Yeager, D. Tryk, U. Landau, J. Wainright, D. Weng, K. Lux, M. Litt, and C. Rogers, J. Elelectrochemical Soc., 141, L46–L48 (1994).
[6] L. Xiao, H. Zhang, T. Jana, E. Scanlon, R. Chen, E.-W. Choe, L. S. Ramanathan, S. Yu, and B. C. Benicewicz, Fuel Cells, 5, 287–295 (2005).
