Abstract
The automated process of coating catalyst layers on gas diffusion electrodes (GDEs) for high-temperature proton exchange membrane fuel cells results inherently into a number of defects. These defects consist of agglomerates in which the platinum sites cannot be accessed by phosphoric acid and which are the consequence of an inconsistent coating, uncoated regions, scratches, knots, blemishes, folds, or attached fine particles—all ranging from μm to mm size. These electrochemically inactive spots cause a reduction of the effective catalyst area per unit volume (cm2/cm3) and determine a drop in fuel cell performance. A computational fluid dynamics (CFD) model is presented that predicts performance variation caused by manufacturing tolerances and defects of the GDE and which enables the creation of a six-sigma product specification for Advent phosphoric acid (PA)-doped polybenzimidazole (PBI)-based membrane electrode assemblies (MEAs). The model was used to predict the total volume of defects that would cause a 10% drop in performance. It was found that a 10% performance drop at the nominal operating regime would be caused by uniformly distributed defects totaling 39% of the catalyst layer volume (~0.5 defects/μm2). The study provides an upper bound for the estimation of the impact of the defect location on performance drop. It was found that the impact on the local current density is higher when the defect is located closer to the interface with the membrane. The local current density decays less than 2% in the presence of an isolated defect, regardless of its location along the active area of the catalyst layer.
Highlights
Advent PBI are phosphoric acid (PA)–doped polybenzimidazole (PBI)-based high-temperature membrane electrode assemblies (MEAs) produced and commercialized by AdventTechnologies Inc. under license from BASF
They are capable of operating in proton exchange membrane fuel cells (PEMFCs) between 120 ◦ C and 180 ◦ C without external humidification, which renders significant benefits over the low-temperature perfluorosulfonic acid (PFSA) membranes such as Nafion
The automated process of coating the catalyst layer on the macro-porous substrate may result in a number of defects (Figure 1) consisting of agglomerates in which the Pt sites cannot be accessed by PA
Summary
Advent PBI (type APM) are phosphoric acid (PA)–doped polybenzimidazole (PBI)-based high-temperature membrane electrode assemblies (MEAs) produced and commercialized by Advent. The automated process of coating the catalyst layer on the macro-porous substrate may result in a number of defects (Figure 1) consisting of agglomerates in which the Pt sites cannot be accessed by PA and which are the consequence of an inconsistent PTFE coating, uncoated regions, scratches, knots, blemishes, folds, or attached fine particles—all ranging from μm to mm size These electrochemically inactive spots cause a reduction of the effective catalyst area per unit volume (cm2 /cm3 ), determine a drop in fuel cell performance, and are subject to a program of continuous improvement to identify the root cause and to reduce the incidence of these defects
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