Modeling of Cold Start Processes in Proton Exchange Membrane Fuel Cells

In this work, a numerical study is carried out to analyze the cold start process of a three-dimensional proton exchange membrane fuel cell (PEMFC) which uses a three-parallel serpentine flow channel design. The investigation is mainly focused on the ice formation during subfreezing startup and how this ice influences the operation of the fuel cell. For this purpose, a transient ice formation model is developed in a computational fluid dynamics (CFD) environment. The model considers sublimation and de-sublimation processes inside the gas diffusion layer and the catalyst layer. To account for the influence of ice on the electrochemical reactions, the local transfer current is reduced depending on the fraction of ice volume present in the porous regions. Validation of the model is performed with available experimental data, and the comparison shows that the model can successfully reproduce both the successful and the failed cold start cases under different initial temperatures. The study identifies two main factors which control the cold start behavior. The first factor is the ionic conductivity of the polymer membrane, which depends strongly on the membrane hydration level. The second factor is the ice accumulation inside the catalyst layer, which blocks the active area and reduces the electrochemical reaction rate. In addition, the simulations provide detailed information about the spatial distribution of ice, especially in the cathode catalyst layer, and show how the local formation of ice can create strong non-uniformities in transport and reaction processes. Overall, the model offers a useful predictive tool for analyzing PEMFC startup at subfreezing conditions and may guide the improvement of design and operation strategies for reliable performance in cold environments.