Investigation of the transient freeze start behavior of polymer electrolyte fuel cells
Mayank Sabharwal, Félix N. Büchi, S. Nagashima, Federica Marone, Jens Eller
Abstract
Understanding the water management in polymer electrolyte fuel cells during sub-zero operation is crucial for designing effective freeze start strategies. This study uses sub-second operando X-ray tomographic microscopy to study the effect of warm-up rate and pre-drying on the water dynamics during non-isothermal freeze starts from −30 °C. A faster warm-up rate and cell pre-drying before freezing improved the cell performance during the freeze start. Imaging showed that during the freeze starts no new water clusters were formed in the cathode gas diffusion layer. Temporary catalyst layer detachment from the micro-porous layer was also observed between −20 to 18 °C due to the hygro-mechanical stresses during the sub-zero operation. Isothermal freeze starts were also performed to study the effect of membrane conductivity and local water flux in the catalyst layer during the sub-zero operation. Higher temperatures and lower operating current densities resulted in an increase in the operation time. Imaging results showed water clusters in the cathode gas diffusion layer for the isothermal freeze starts from −15 to 0 °C after 6 C/cm2 charge was produced.