Localized Study of the CCM with Graded Ionomer and Catalyst Loading across the X-Y and Z Directions Using Current Scan Shunt

Abstract

In project CAMELOT, it is aimed to diagnose the fundamental transport properties that limit performance in state-of-the-art (SoA) and prototype beyond-SoA Membrane Electrode Assembly (MEA)s and materials. To accomplish this goal, a series of in-situ characterization methods are used to create correlations between the observed performance, voltage loss breakdowns at the cell level, and the fundamental material property characteristics of the MEA and MEA materials. To accomplish this goal, thin Catalyst Coated Membrane (CCM) with low Pt loading is used as target study material; and the logic for using thinner layers in each of the MEA components is clear: thinner constituent layers (membrane, catalyst layers, microporous layers (MPL), gas diffusion layers (GDL)) means shorter transport distances for protons, oxygen, hydrogen and electrons and should thus reduce the associated transport losses. Thin‐layer X‐Y and Z direction graded catalyst layers are developed in project CAMELOT to optimize porosity, ionomer content and catalyst loading across the X‐Y and Z directions of the CCM. For the X‐Y direction CAMELOT matches the catalyst layer composition to the conditions at different locations within the flow field. For example, the porosity and ionomer content of the catalyst layer near the outlet of the flow field should be tuned for significantly wetter conditions than at the flow field inlet. For Z direction CAMELOT matches the catalyst layer composition to the conditions of the membrane and the GDL layer. The goal is to ensure that at each point in the active area, the catalysts can operate as close to their maximum (kinetically limited) performance as possible by minimizing mass transport limitations under the conditions that prevail at the different locations. For example, the porosity and ionomer content of the catalyst layer near the outlet of the flow field should be tuned for significantly wetter conditions than at the flow field inlet. Current Scan Shunt (CSS) is used as a convenient tool to measure real-time current density and temperature distribution within the fuel cell in situ operando, to analyze the cell behavior depending on the components and the direction of the grading catalyst layer on the developed CCMs. The experimental work will later be supplemented by a theoretical analysis carried out in the modelling work and, together, the modelling and experimental analysis can be used to construct a complete picture of correlated relationships between the MEA structure and properties and the associated voltage loss causes of the performance limitations for current SoA materials.