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

Matias A Quiroga,Kourosh Malek,Alejandro A Franco

doi:10.1149/2.0931514jes

Abstract

We report a multi-paradigm model of the membrane chemical degradation in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), by combining Coarse-Grained Molecular Dynamics (CGMD) and a multiscale cell performance model. CGMD is used to generate structural databases that relate the amount of detached (degraded) ionomer sidechains with the water content and the resulting PEM meso-microporous structure. The multiscale cell performance model describes the electrochemical reactions and transport mechanisms occuring in the electrodes from an on-the-fly coupling between Kinetic Monte Carlo (KMC) sub-models parametrized with Density Functional Theory (DFT) data and (partial differential equations-based) continuum sub-models. Furthermore, the performance model includes a kinetic PEM degradation sub-model which integrates the CGMD database. The cell model also predicts the instantaneous PEM sidechain content and conductivity evolution at each time step. The coupling of these diverse modeling paradigms allows one to describe the feedback between the instantaneous cell performance and the intrinsic membrane degradation processes. This provides detailed insights on the membrane degradation (sidechain detachment as well as water reorganization within the PEM) during cell operation. This novel modeling approach opens interesting perspectives in engineering practice to predict materials degradation and durability as a function of the initial chemical composition and structural properties in electrochemical energy conversion and storage devices.

Highlights

From the second half of the twentieth century, Polymer Electrolyte Membrane Fuel Cells (PEMFCs) have attracted much attention due to their potential as a clean power source for vehicles traction
We reported the first models aiming at account for the instantaneous feedback between the PEM chemical degradation and the electrochemical and transport processes in a PEMFC.[2,34,35,36,37]
We have presented a multiscale mesostructurally resolved model allowing predicting the PEM chemically induced aging upon the PEMFC operation conditions

Summary

Introduction

From the second half of the twentieth century, Polymer Electrolyte Membrane Fuel Cells (PEMFCs) have attracted much attention due to their potential as a clean power source for vehicles traction. Meso/micro-structural degradation leading to the PEMFC components aging is attributed to several complex physicochemical mechanisms not yet completely understood. The associated components meso/micro-structural changes translate into irreversible longterm cell power degradation.[1,2,3] For instance, dissolution and redistribution of the catalyst reduces the specific catalyst surface area and the electrochemical activity. Apart from mechanical degradations such as thinning and pinhole formations,[4] chemical and electrochemical degradations can take place in the PFSA-based membranes and in the ionomer inside the CLs.[5]. Significant permeation of the reactants across PEM, in particular oxygen from the cathode to the anode, has been often experimentally reported as being the major cause of PEM chemical degradation.[6,7,8] The formation of hydrogen peroxide (H2O2) at the anode CL9,10 is attributed to the following reaction. Formation of H2O2 may occur at the cathode CL as part of the Oxygen Reduction Reaction (ORR), O2 + 2 H+ + 2 e− → H2O2

Methods

Results

Conclusion