Abstract
The loss of electrochemical active surface area (ECSA) at the cathode is one of the main causes of performance degradation in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). In order to investigate the catalyst degradation and the influence of the operating conditions we develop a multiscale degradation model which includes the formation and reduction of platinum oxides, platinum dissolution, particle growth due to Ostwald ripening, platinum ion transport through the ionomer and platinum band formation in the membrane. This degradation model is coupled with a 2D PEMFC performance model and predictions regarding ion concentration, ECSA evolution and particle growth are validated with dedicated experiments and literature data. Degradation under several AST protocols and under steady state operation are compared and discussed. The importance of a spatially resolved catalyst degradation model is conveyed by the occurrence of a depletion zone in the catalyst layer close to the membrane due to the platinum migration into the membrane. By comparing the correlation between platinum mass loss in the catalyst layer and the ECSA loss we conclude that catalyst degradation under AST conditions with nitrogen is not representative for the degradation under normal operation.
Highlights
Several models have been developed in the past to describe one or several of the mechanisms described above.[14]
By coupling novel submodels for platinum oxidation, platinum dissolution, Ostwald-ripening and platinum band formation with a 2D single cell performance model the degradation model presented in this manuscript is capable of accurately describing the catalyst degradation under steady-state and transient operation with a single set of parameters
In the Coupling with the cell model section we describe how the degradation model is coupled with the physical 2D Polymer Electrolyte Membrane Fuel Cells (PEMFCs) model in our modeling framework NEOPARD-X.26,27
Summary
We introduce the physical model describing the catalyst degradation. The multiscale model includes platinum oxidation and reduction, platinum dissolution, particle growth and platinum band formation which are described in the following subsections. Comment fitted fitted assumed fitted fitted fitted fitted fitted fitted fitted fitted 17 assumed fitted 17 29 17 fitted assumed assumed assumed who attributed this effect to a slow place exchange between the oxygen and platinum atoms.[28] The authors proposed a three-step mechanism consisting of one fast initial oxidation step followed by a slow irreversible place exchange and an irreversible reduction of the oxides. This model was not specified in terms of the reaction kinetics for these three steps.
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