To advance the technology of polymer electrolyte membrane fuel cells, material development is at the forefront of research. This is especially true for membrane electrode assembly, where the structuring of its various layers has proven to be directly linked to performance increase. In this study, we investigate the influence of the various ingredients in the cathode catalyst layer, such as ionomer content, catalyst loading and catalyst type, on the oxygen and ion transport using a full parametric analysis. Using two types of catalysts, 40 wt.% Pt/C and 60 wt.% Pt/C with high surface area carbon, the ionomer/carbon content was varied between 0.29–1.67, while varying the Pt loading in the range of 0.05–0.8 mg cm⁻². The optimum ionomer content was found to be dependent on the operating point and condition, as well as catalyst loading and type. The data set provided in this work gives a starting point to further understanding of structured catalyst layers.

In this work we investigate the effect of platinum loading and layer thickness on cathode catalyst degradation by a comprehensive in situ and STEM-EDS characterization. To decouple the effect of the platinum loading and layer thickness from each other, the experiments were categorized in two sets, each with cathode loadings varying between 0.1 and 0.4 mg_Pt cm⁻²: (i) Samples with a constant Pt/C ratio and thus varying layer thickness, and (ii) samples with varying Pt/C ratios, achieved by dilution with bare carbon, to maintain a constant layer thickness at different platinum loadings. Every MEA was subjected to an accelerated stress test, where the cell was operated for 45,000 cycles between 0.6 and 0.95 V. Regardless of the Pt/C ratio, a higher relative loss in electrochemically active surface area was measured for lower Pt loadings. STEM-EDS measurements showed that Pt was mainly lost close to the cathode—membrane interface by the concentration driven Pt²⁺ ion flux into the membrane. The size of this Pt-depletion zone has shown to be independent on the overall Pt loading and layer thickness, hence causing higher relative Pt loss in low thickness electrodes, as the depletion zone accounts for a larger fraction of the catalyst layer.

The effect of ionomer to carbon (I/C) weight ratio and relative humidity (RH) on cathode catalyst degradation was investigated by comprehensive in situ characterization. Membrane electrode assemblies (MEA) with I/C ratios of 0.5, 0.8 and 1.2 were subjected to an accelerated stress test performed at 40, 70 and 100% RH. The results show an increasing loss in electrochemical active surface area (ECSA) for both higher I/C ratios and RH during voltage cycling. To differentiate between ionomer and water connected ECSA, carbon monoxide stripping measurements were performed at varying RH. Before degradation, all MEAs show comparable total ECSA values, while higher I/C ratios lead to a larger fraction of ionomer connected ECSA. After degradation, ECSA measurements of the lowest I/C ratio showed a relatively higher loss of Pt in contact with ionomer than Pt in contact with water, while an opposite trend was observed for higher I/C ratios. H₂/N₂ impedance measurements showed drastically increasing protonic catalyst layer resistances for decreasing RH especially at low I/C ratios, which might hinder Pt²⁺ ion diffusion towards the membrane, hence decreasing the ECSA loss. Limiting current measurements show increasing molecular O₂ diffusion resistances at end of test for samples with higher I/C ratios and higher ECSA loss.

The composition and morphology of the cathode catalyst layer (CCL) have a significant impact on the performance and stability of polymer electrolyte membrane fuel cells (PEMFC). Understanding the primary degradation mechanism of the CCL and its influencing factors is crucial for optimizing PEMFC performance and durability. Within this work, we present comprehensive in-situ characterization data focused on cathode catalyst degradation. The dataset consists of 36 unique durability tests with over 4000 testing hours, including variations in the cathode ionomer to carbon ratio, platinum on carbon ratio, ionomer equivalent weight, and carbon support type. The applied accelerated stress tests were conducted with different upper potential limits and relative humidities. Characterization techniques including IV-curves, limiting current measurements, electrochemical impedance spectroscopy, and cyclic voltammetry were employed to analyse changes in performance, charge and mass transfer, and electrochemically active surface area of the catalyst. The aim of the dataset is to improve the understanding of catalyst degradation by allowing comparisons across material variations and provide practical information for other researchers in the field.

We present a physical degradation model which simulates the evolution of the cathode catalyst layer nanomorphology and associated catalyst surface area in the course of potential-induced ageing. By coupling to the morphology model featured in Part I, the effects of the pore, particle and ionomer distributions and resulting nanoscale interfaces in each individual material are taken into account. Specifically, the model discriminates between catalyst ageing on the support surface and inside primary pores of the support. For model validation, catalyst utilization data in terms of active surface area measured at varying relative humidity is used. These data are sensitive to a variety of electrode properties such as support porosity, catalyst loading and size and ionomer loading. Simulations are compared against data from 15 samples manufactured in-house using different materials and aged in different conditions. In-depth analysis of simulation results identifies the model as a valuable tool to establish a link between electrode composition and nanomorphology as well as between nanomorphology and expected degradation.

We present a physical model of the cathode catalyst layer morphology which simulates the electrochemically active catalyst surface area at varying degrees of humidification. The model considers pore, particle and ionomer distributions and resulting interfaces on the nanoscale to create a unique mathematical representation of each material. Specifically, the model discriminates between catalyst particles on the support surface and inside primary pores of the support and their respective connection to the proton-conducting phase. Catalyst particles may be protonically activated by coverage with ionomer or water or be protonically inaccessible. The exact configuration depends on the particle size and location as well as the cell operating conditions, sensitizing the simulated catalyst utilization to these properties. Model results are compared against data for five samples with different support materials and ionomer loadings manufactured in-house. Further, trends in catalyst utilization which were observed in recent literature are reproduced with the model. This work provides a comprehensive analysis of material configurations and simulations at begin of test. In Part II, the presented model is integrated into a degradation model to predict the evolution of the electrode morphology and catalyst utilization during ageing.