Hydrogen starvation is regarded as one of the most critical and harmful conditions in state-of-the-art polymer electrolyte membrane fuel cells (PEMFCs). Even when the fuel cell is operated with sufficient hydrogen stoichiometry, local hydrogen starvation can occur due to reactant maldistribution, e.g. by blockage of certain area of the flow field by the presence of liquid water. In the starved area, the cathodic catalyst layer (CL) suffers high interfacial potential difference which induces irreversible degradation reactions, most likely carbon corrosion. The resulting structural changes and electrochemical active area losses severely reduce the fuel cell performance [1].

Most papers in the literature with focus on modeling of hydrogen starvation phenomena conducted simulations under steady state [2, 3]. In the present study, we introduce a two-dimensional numeric model with transient nature, which reflects the dynamic behavior of a fuel cell from the onset of local starvation induced by blockage of the flow field. Besides the relevant electrochemical reactions in both CLs, the model takes transport phenomena of hydrogen, oxygen and protons into account. Solving of the resulting partial differential equation systems is done using the finite element solver in MATLAB. Additionally, we utilize a “reversed cell” to experimentally provide necessary parameter inputs under various operational conditions for the kinetics modeling. The numeric model is further validated by measurements using a segmented cell.

This work sheds light into the dynamic response of the cell under starvation conditions as well as influences of operation conditions and certain transport parameters of the GDL and the CL on the degradation phenomena. With the onset of the partially blocked flow field, strong deviation of current density and protonic potential is observed in the starved area. Depending on the operational condition (e.g. applied galvanostatic current density, initial hydrogen concentration) and the applied transport properties, we show various extent of hydrogen depletion in the starved region over time. We also demonstrate the time it takes from normal operation to severe hydrogen depletion where the cell starts suffering from reversed current and carbon corrosion.

Literature

[1] Paul, T. Y., Gu, W., Zhang, J., Makharia, R., Wagner, F. T., & Gasteiger, H. A. (2009). Carbon-support requirements for highly durable fuel cell operation. In Büchi, F. N., Inaba, M., Schmidt, T. J. (Ed.), Polymer electrolyte fuel cell durability (pp. 29-53). Springer, New York, NY.

[2] Yang, X. G., Ye, Q., & Cheng, P. (2012). In-plane transport effects on hydrogen depletion and carbon corrosion induced by anode flooding in proton exchange membrane fuel cells. International Journal of Heat and Mass Transfer, 55(17-18), 4754-4765.

[3] Ohs, J. H., Sauter, U., Maass, S., & Stolten, D. (2011). Modeling hydrogen starvation conditions in proton-exchange membrane fuel cells. Journal of Power Sources, 196(1), 255-263.