Abstract
Durability targets of automotive polymer electrolyte membrane fuel cells (PEMFCs) could be crucially threatened by local hydrogen starvation, typically induced by local blockage of gas channels. To gain a deep insight on the evolving of such starvation events and related carbon corrosion losses, we have developed a numerical model with transient nature that includes detailed transport phenomena and electrochemistry. Special focus is on water transport and sensitivity of relative humidity (RH) on both anode and cathode sides, whose influences were commonly neglected in starvation-related modeling studies. Utilizing the model, we show the dominating effect of in-plane hydrogen convection within the anode gas diffusion layer, which is again determined by the accumulation of other gas species including water vapor. We demonstrate how this is again linked with the water management throughout the fuel cell. Furthermore, water transport is shown to affect local current density and membrane oxygen permeability, both being critical influential factors regarding the severity of a local starvation event. The developed model is validated by conducting transient current density distribution measurements. As RH levels are crucial operational conditions within automotive PEMFCs, this work serves as useful input towards development of future operation strategies for better PEMFC durability.
Highlights
Notes on SΦConsumption by HOR Consumption by ORR, production by OER Total current Total current Production, consumption by ORR, OER, COR terms are related with electrochemistry which is described in very detail in the Supplementary Material
Symbol c d D E0 Eac ECSA EW F i i0 iV j K Kmemb LMprR Rct rf SΦ t T tdepl u⃗ x y
We investigate the dynamic response of a polymer electrolyte membrane fuel cells (PEMFCs) during a local hydrogen starvation event, with respect to gas and current density distribution as well as carbon corrosion amount
Summary
Consumption by HOR Consumption by ORR, production by OER Total current Total current Production, consumption by ORR, OER, COR terms are related with electrochemistry which is described in very detail in the Supplementary Material. The CCM model requires the electric potential (φe) on the anode side This is evaluated by sub-model II, which needs inputs of current densities from sub-model III. Besides the coupling of the sub-models and the iteration loop, sub-model III still requires the cell voltage as an additional input (boundary condition for φe on the cathode side). This value is unknown a priori if the cell is operated in galvanostatic mode (i.e. controlling overall current of the cell). We define case No 3 as the simulation base case where we show the overall observations during the modeled local starvation event (section “Overall observations in the base simulation case”)
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