Ice-Crystallization Kinetics and Water Movement in Gas-Diffusion and Catalyst Layers

Under subfreezing conditions, ice forms in the gas-diffusion (GDL) and catalyst layers (CL) of proton-exchange-membrane fuel cells (PEMFCs), drastically reducing cell performance. Although a number of strategies exist to prevent ice formation, there is little fundamental understanding of ice-crystallization mechanisms and kinetics within PEMFC components. We use differential scanning calorimetry (DSC) to measure ice-crystallization kinetics in both the GDL and CL. Nonlinear ice-crystallization rate expressions are developed from a convolution integral over nucleation and growth rates, following Johnson-Mehl-Avrami-Kolmogorov theory. Quantitative agreement is found with the DSC data. Validated rate expressions are now available for predicting ice-crystallization kinetics within both GDL and CL components of PEMFCs.