Wenmei Liu1,2,Jongmin Li1,Yen-Chun Chen1,Yang Yao2,Sonja Neuhaus3,Alok Goel3,Thomas Justus Schmidt1,2,Pierre Boillat1
Paul Scherrer Institute1,ETH Zürich2,University of Applied Sciences and Arts Northwestern Switzerland (FHNW)3
Wenmei Liu1,2,Jongmin Li1,Yen-Chun Chen1,Yang Yao2,Sonja Neuhaus3,Alok Goel3,Thomas Justus Schmidt1,2,Pierre Boillat1
Paul Scherrer Institute1,ETH Zürich2,University of Applied Sciences and Arts Northwestern Switzerland (FHNW)3
Polymer electrolyte fuel cells (PEFCs) are promising alternatives for automotive and portable applications thanks to zero-emission, low operating temperature, and fast refueling. Water management is a challenge for successful cold-start, as well as stable, long-lasting, and high PEFC performance at subzero temperatures. Sudden freezing of supercooled water leads to rapid voltage degradation, causing cold-start failure<sup>1,2</sup>. In addition, it causes irreversible damage to cell components, including the membrane, catalyst layer, and gas diffusion layer (GDL), so-called freeze-thaw<sup>3,4</sup>, which results in a significant reduction of PEFC lifetime.<br/><br/>Our previous work has shown that GDLs with patterned wettability improved water management and cell performance<sup>5,6</sup> in normal operational conditions. In this presentation, we will show the effects of wettability-patterned GDLs on preventing ice propagation with the following parameters being systematically investigated: GDL substrate, water saturation level, hydrophobic polymeric coating, coating loads, and wettability pattern dimensions. Ex-situ differential scanning calorimetry (DSC) and in-situ advanced calorimetry were used as calorimetric techniques to detect the onset of freezing temperatures of water in GDLs. X-ray tomography was used to visualize the water distribution inside GDLs.<br/><br/>The designed pathways allow the effective separation of water and gas. Individual freezing events were found to happen above -15 <sup>o</sup>C and below -25 <sup>o</sup>C in the patterned Toray (250 µm hydrophilic- 1000 µm hydrophobic), which shows the effective prevention of ice propagation in GDLs. Thanks to the improved water management, the ice-free area can diffuse reactant gaseous to allow continuous operation of the cell, which improves the cold-start capability.<br/><br/>1. Wang, S., Sun, Y., Huang, F. & Zhang, J. Freezing Site of Super-Cooled Water and Failure Mechanism of Cold Start of PEFC. <i>Journal of The Electrochemical Society</i> <b>166</b>, F860–F864 (2019).<br/>2. Jiao, K., Alaefour, I. E., Karimi, G. & Li, X. Cold start characteristics of proton exchange membrane fuel cells. <i>International Journal of Hydrogen Energy</i> <b>36</b>, 11832–11845 (2011).<br/>3. Alink, R., Gerteisen, D. & Oszcipok, M. Degradation effects in polymer electrolyte membrane fuel cell stacks by sub-zero operation—An in situ and ex situ analysis. <i>Journal of Power Sources</i> <b>182</b>, 175–187 (2008).<br/>4. Yan, Q., Toghiani, H., Lee, Y.-W., Liang, K. & Causey, H. Effect of sub-freezing temperatures on a PEM fuel cell performance, startup and fuel cell components. <i>Journal of Power Sources</i> <b>160</b>, 1242–1250 (2006).<br/>5. Forner-Cuenca, A. <i>et al.</i> Engineered Water Highways in Fuel Cells: Radiation Grafting of Gas Diffusion Layers. <i>Advanced Materials</i> <b>27</b>, 6317–6322 (2015).<br/>6. Manzi-Orezzoli, V., Siegwart, M., Scheuble, D., Schmidt, T. J. & Boillat, P. Impact of the Microporous Layer on Gas Diffusion Layers with Patterned Wettability II: Operando Performance and Water Distribution Analysis by Neutron Imaging. <i>J. Electrochem. Soc.</i> <b>167</b>, 064521 (2020).