A structure-based performance model for Cathode Catalyst Layers (CCLs) of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) is presented. A CCL is the major competitive ground for mass transport, electrochemical reaction, and vaporization in a PEMFC. Analytical solutions for the case of fast proton transport have revealed that the CCL plays a vital role in the conversion of liquid water to vapor and in regulating water fluxes towards Polymer Electrolyte Membrane (PEM) and Gas Diffusion Layer (GDL). Critical values of proton conductivity and oxygen transport coefficient are introduced to distinguish different regimes of operation for these transport processes. Subsequently, the role of the porous structure and of liquid water accumulation for the performance of CCL in PEMFCs is explored. The non-linear spatial coupling between liquid water accumulation and oxygen depletion triggers critical effects and bistability in current-voltage response curves. Stability diagrams are proposed as novel tools for assessing CCL performance.
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