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Fuel Cell Diagnostics through Neutron Imaging

In a first part, the recent advances at PSI in neutron imaging and combined diagnostics methods will be presented. The advantages and limitations of mass transport characterization methods such as electrochemical impedance spectroscopy (EIS), limiting current density and our recently developed pulsed gas analysis (PGA) (5) will be presented. Additionally, the choice of test cell hardware and its impact on results from these methods will be discussed.

In a second part, a selection of experimental results will show how the combination of imaging and advanced electrochemical characterization can bring a new understanding to the mass transport limiting processes. A particular attention will be given to the choice of gas diffusion layer (GDL) material characteristics such as the amount of hydrophobic coating and the presence of a microporous layer (MPL).

1. R. Satija, D. L. Jacobson, M. Arif and S. A. Werner, *J Power Sources* **129**, 238 (2004).

2. J. P. Owejan, J. J. Gagliardo, J. M. Sergi, S. G. Kandlikar and T. A. Trabold, *Int J Hydrogen Energ*, **34** 3436 (2009).

3. D. Kramer, J. B. Zhang, R. Shimoi, E. Lehmann, A. Wokaun, K. Shinohara and G. G. Scherer, *Electrochim Acta* **50**, 2603 (2005).

4. A. B. Geiger, A. Tsukada, E. Lehmann, P. Vontobel, A. Wokaun and G. G. Scherer, *Fuel Cells* **2**, 92 (2003).

5. P. Boillat, P. Oberholzer, A. Kaestner, R. Siegrist, E. H. Lehmann, G. G. Scherer and A. Wokaun, *J Electrochemical Soc* **159**, F210 (2012).

6. P. Oberholzer, P. Boillat, R. Siegrist, R. Perego, A. Kastner, E. Lehmann, G. G. Scherer and A. Wokaun, *J Electrochemical Soc* **159**, B235 (2012).

7. J. Biesdorf, P. Oberholzer, F. Bernauer, A. Kaestner, P. Vontobel, E. H. Lehmann, T. J. Schmidt and P. Boillat, *Phys Rev Lett* **112**, 248301 (2014).

Figure caption:

**Figure 1** – Top: Neutron radiograms of a differential fuel cell operating at 1 A/cm2 with different humidities. Bottom: corresponding transport losses measured using our PGA method. Reproduced from ref. (5).