Polymer electrolyte membrane (PEM) fuel cells are rapidly becoming a viable, alternative clean power source for automobile and stationary applications in the emerging hydrogen economy. However, several key issues need to be addressed before PEM fuel cells can be used to routinely power automobiles and homes. These include improving performance by proper liquid-water management, improving durability by understanding how cell stacks fail, and developing PEM fuel cells for operation in harsher (e.g., freezing) environments.

Liquid water droplets emerging from the gas diffusion layer (GDL) surface in an operating PEM fuel cell

Liquid-water droplets on cathode GDL surface (GDL is into the page)

To help address these issues, Sandia researchers are focusing on achieving a better fundamental understanding and elucidating the mechanisms of key phenomena affecting the startup, long-term performance, reliability, and durability of PEM fuel cells. Our work, sponsored by the Laboratory-Directed Research & Development program, involves both computational modeling (analytical, semi-analytical, and numerical via the finite element method) and experiments for phenomena discovery and model validation.

Predicted and measured instability of water droplets at the gas diffusion layer (GDL) / gas flow channel (GFC) interface as a function of contact angle hysteresis (unstable refers to instantaneous removal)

Our ongoing and future investigations cover the following areas:

• Hydrogen fuel and oxygen reactant transports along gas flow channels (GFC) and through respective (GDL) gas diffusion layers
• Hydrogen oxidation and oxygen reduction reactions in catalyst layers
• Proton and water transports through polymer electrolyte membranes
• Simultaneous liquid-water and oxygen transports through GDLs having non-uniform hydrophobic/hydrophilic pore surfaces and in GFCs
• Liquid-water removal at GDL/GFC interface via shearing and/or evaporation
• Membrane failure due to chemical and stress-induced degradation
• Platinum dissolution and catalyst “poisoning” by contaminants such as carbon monoxide
• Carbon corrosion (GDLs are made of carbon paper)
• GDL and catalyst layer (CL) failures due to liquid water freezing
• Stress/strain evolution inside the (membrane electrode assembly) and stack
• Startup and operation in freezing (i.e., at or below 32° F) environments

Our objectives are to (1) develop constitutive and phenomenological models that elucidate underlying mechanisms of key phenomena, and (2) develop an integrated and validated PEM fuel cell computer model that incorporates essential phenomena and can be used to simulate PEM fuel cell performance under practical operating conditions.

We are collaborating on this work with researchers at Pennsylvania State University’s Electrochemical Engine Center, directed by Prof. Chao-Yang Wang.

Selected Publications:

1. K. S. Chen, M. A. Hickner, and D. R. Noble, “Simplified models for predicting the onset of liquid water droplet instability at the gas diffusion layer/gas flow channel interface”, accepted for publication in Int. J. Energy Research (2005).
2. U. Pasaogullari, C.-Y. Wang, and K. S. Chen, “Two-phase transport in polymer electrolyte fuel cells with by-layer cathode gas diffusion media”, in press in J. Electrochem. Soc. (2005).
3. M. A. Hickner and K. S. Chen, “Experimental studies of liquid water droplet growth and instability at the gas diffusion layer/gas flow channel interface”, accepted for publication in Proceedings of FUELCELL05, paper # FUELCELL2005-74118 (2005).
4. K. S. Chen and M. A. Hickner, “A new constitutive model for predicting proton conductivity in polymer electrolytes”, in Proceedings of IMECE04, paper # IMECE2004-60848 (2004).
5. D. R. Noble and K. S. Chen, “Elucidating water-droplet removal in polymer electrolyte fuel cells”, in Proceedings of IMECE04, paper # IMECE2004-62129 (2004).
6. U. Pasaogullari, C.-Y. Wang, and K. S. Chen, “Liquid water transport in polymer electrolyte fuel cells with multi-layer diffusion media”, in Proceedings of IMECE04, paper #IMECE2004-59283 (2004).