Modeling the Morphological Effects of Catalyst and Ionomer Loading on Porous Carbon Supports of PEMFC

Abstract

We present a model of the cathode catalyst layer morphology before and after loading a porous catalyst support with Pt and ionomer. Support nanopores and catalyst particles within pores and on the support surface are described by size distributions, allowing for qualitative processes during the addition of a material phase to be dependent on the observed pore and particle size. A particular focus is put on the interplay of pore impregnation and blockage due to ionomer loading and the consequences for the Pt/ionomer interface, ionomer film thickness and protonic binding of particles within pores. We used the model to emulate six catalyst/support combinations from literature with different porosity, surface area and pore size distributions of the support as well as varying particle size distributions and ionomer/carbon ratios. Besides providing qualitatively and quantitatively accurate predictions, the model is able to explain why the protonically active catalyst surface area has been reported to not increase monotonically with ionomer addition for some supports, but rather decrease again when the optimum ionomer content is exceeded. The proposed model constitutes a fast translation from manufacturing parameters to catalyst layer morphology which can be incorporated into existing performance and degradation models in a straightforward way.

The Effect of Ionomer to Carbon Ratio and Relative Humidity on Cathode Catalyst Degradation in PEM Fuel Cells

“…Kobayashi et al 20 reported in their study that the I/C ratio can impact the impregnation of pores by ionomer, with higher ionomer contents preventing the ionomer from accessing the pore volume, leading to decreasing ECSA values. Scherzer et al 12 presented a comprehensive catalyst morphology model, introducing a minimum impregnatable pore radius at a given I/C ratio. In this work we assume that ionomer mainly covers surface Pt and does not impregnate smaller pores-even though it should be noted that there still might be a fraction of larger pores that are accessible by ionomer.…”

“…They found higher particle growth rates and increased Pt ion diffusion into the membrane for ionomers with higher proton exchange capacities. In an earlier work, 12 we developed a state of health model to describe cathode catalyst degradation under varying operating conditions and load profiles. The model was validated based on experimental data where the cell was cycled for 300,000 potential cycles at varying temperatures and relative humidities.…”

“…Scherzer et al 12 published a comprehensive cathode catalyst morphology model which describes how nano morphological as well as global properties of the CCL depend on particle size distribution, pore size distributions, and ionomer loading. By defining a critical pore radius above which pores are impregnatable by ionomer they were able to simulate the effect of a non-monotonic correlation between protonically active ECSA and increasing I/C ratio which Kobayashi et al 20 had measured.…”

Platinum Surface Oxide and Oxygen Reduction Reaction Kinetics during Transient Fuel Cell Operation

“…We'll first focus on the ORR kinetic model for Pt/V, because for PtCo/ HSC, we need to include not only the thermodynamic and kinetic contribution terms of the Pt alloy catalyst, but also the terms for proton and oxygen transport to Pt particles inside the porous carbon support which is not well understood. 60,61 To help understand the transient behavior of ORR activity, recall the Pt oxide growth and ORR activity decay over time. As shown in Fig.…”

A Critical Review on Artificial Intelligence for Fuel Cell Diagnosis

“…The proton species present in the acid group are dissociated and become solvated when the membrane is hydrated. Inside the polymer, the solvated protons are free and produce electrolyte conductivity [20,[27][28][29][30]. PEMFCs are capable of having a power output of 1-300 kW with a high cost [17].…”