Microstructure-Based Modeling of Aging Mechanisms in Catalyst Layers of Polymer Electrolyte Fuel Cells

Abstract

This work is comprised of a versatile multiscale modeling of carbon corrosion processes in catalyst layers (CLs) of polymer electrolyte fuel cells (PEFCs). Slow rates of electrocatalytic processes in CLs and materials aging are the main sources of voltage loss in PEFCs under realistic operating conditions. We combined microstructure data obtained from coarse-grained molecular dynamics (CGMD) simulations with a detailed description of the nanoscale elementary kinetic processes and electrochemical double-layer effects at the catalyst/electrolyte and carbon/electrolyte interfaces. We exclusively focused on morphology and microstructure changes in the catalyst layer of PEFCs as a result of carbon corrosion. By employing extensive CGMD simulations, we analyzed the microstructure of CLs as a function of carbon loss and in view of ionomer and water morphology, water and ionomer coverage, and overall changes in carbon surface. These ingredients are integrated into a kinetic model, which allows capture of the impact of the structural changes on the PEFC performance decay. In principle, such multiscale simulation studies allow a relation of the aging of CLs to the selection of carbon particles (sizes and wettability), the catalyst loading, and the level of ionomer structural changes during the CL degradation process.

A Multiparadigm Modeling Investigation of Membrane Chemical Degradation in PEM Fuel Cells

“…CGMD simulations.-The details of the computational approach based on CGMD simulations are explained elsewhere [43][44][45]50 and is developed in two major steps. In the first step, Nafion chains, water and hydronium molecules are replaced by corresponding spherical beads with predefined sub-nanoscopic length scale.…”

“…The technical feasibility of the combination between performance cell models and CGMD databases have been already demonstrated by us for describing carbon corrosion in PEMFC CLs. 50 To the best of our knowledge, we report here the first modeling-based analysis of the PEM meso/microstructure upon its degradation and continuous feedback with the cell performance.…”

Optimization of catalyst ink composition for the preparation of a membrane electrode assembly in a proton exchange membrane fuel cell using the decal transfer

“…For intermediate-and high-current polarization, the ionomer-aging effect resulted in similar degree of voltage loss, which is approximately 50 mV at 2.0 A cm À2 . By considering moleculardynamics simulation result from Malek and Franco [17], the low-current polarization data suggests that low NCR MEA may prevent early transition of Nafion-CB surfaces from hydrophobic to hydrophilic state, which directly accelerate carbonsupport oxidation. Because transient variations in CL microstructures are dependent on carbon-support selection [33], further studies are recommended to examine carboncorrosion durability of the low-NCR MEAs by employing graphitized-carbon supports.…”

“…This is the main reason why most DT experiments have been conducted with isopropyl alcohol, glycerol or glycerol-like solvents [10e13], such as ethylene glycol, propylene glycol, etc. According to recent molecular-dynamics simulations [17] and voltammetric experiments [18], catalyst ink composition is crucial, because interfacial properties arising from NafionPt or Nafion-carbon relation can be varied. In addition, Bender et al [19] reported that preparing 10 MEA samples took 24 h of annealing duration when DT was applied.…”

A Multi-Paradigm Computational Model of Materials Electrochemical Reactivity for Energy Conversion and Storage

“…For example, activation barriers for elementary reaction steps can be extracted from Density Functional Theory (DFT) calculations 8 and then injected into Transition State Theory (TST) Eyring's expressions to estimate the parameters which are used to solve Mean Field (MF) kinetic models simulating the evolution of the reactants, intermediate reaction species and products. 9,10 Alternatively, direct multiparadigm multiscale models consist in coupling "on-the-fly" models developed in the frame of different paradigms. For instance, continuum equations describing the transport phenomena of multiple reactants in a porous electrode may be coupled with atomistically-resolved simulations describing electrochemical reactions among these reactants.…”