The state of health of polyfluorinated sulfonic-acid ionomer membranes (e.g. Nafion®) in low-temperature proton exchange membrane fuel cells (LT-PEMFCs) is negatively influenced by degradation phenomena occurring during their operation. As a consequence, the performance and durability of the membrane are decreased. In this article, we focus on simulating and predicting chemical membrane degradation phenomena using a holistic zero-dimensional kinetic framework. The knowledge of chemical degradation mechanisms is widely spread. We have collected and evaluated an extensive set of chemical mechanisms to achieve a holistic approach. This yields a set of 23 coupled chemical equations, which provide the whole cause and effect chain of chemical degradation in LT-PEMFCs (based on the Fenton reaction between Fe²⁺ and H₂O₂ via the attack of hydroxyl radicals on the membrane, loss of ionomer moieties and emission of fluoride). Our kinetic framework allows the reproduction of experimentally accessible data such as fluoride emission rates and concentrations of ionomer moieties (from both in situ and ex situ tests). We present an approach, which allows estimations of the membrane lifetime based on fluoride emission rates. In addition, we outline the demetallation of Fe–N–C catalysts as a source of additional harmful iron species, which accelerate chemical membrane degradation. To demonstrate the expandability and versatility of the kinetic framework, a set of five chemical equations describing the radical scavenging properties of cerium agents is coupled to the main framework and its influence on membrane degradation is analysed. An automated solving routine for the system of coupled chemical equations on the basis of the chemical kinetic simulation tool COPASI has been developed and is freely accessible online (http://ptc-pc-139.tugraz.at/cgi-bin/Membrane_Degradation/).

The degradation of the catalyst layer represents one of the main limiting factors in a wider adoption of fuel cells. The identification of the contributions of different mechanisms of catalyst degradation, namely the Ostwald ripening and particle agglomeration, is an important step in the development of mitigation strategies for increasing fuel cell reliability and prolonging its life time.In this paper, the degradation phenomena in high temperature polymer electrolyte membrane fuel cell (HT‐PEMFC) are analyzed using a physically‐based model of fuel cell operation and catalyst degradation, describing carbon corrosion, platinum dissolution and consequent growth of catalyst particles. The model results indicate significantly different time dependence of catalyst particle growth resulting from different mechanisms: linear growth in the case of particle agglomeration and root‐like time dependence for the Ostwald ripening.Based on these results, a new analytic method is proposed, performed by the fitting of a test root‐function to the time profile of the particle size growth and using best‐fit parameters to identify the prevailing growth mechanism. Using this method on a particle growth time trace deduced from in situ cyclic voltammetry measurement during HT‐PEMFC degradation, we are able to identify the agglomeration as the main mechanism of catalyst particle grow.

The present study showcases the importance of temperature and potential window for evaluation of Pt-based supported electrocatalyst stability. A platinum based commercial material with an average size of Pt nanoparticles between 2–3 nm (Pt/C) and its thermally annealed analogue with an average particle size of ∼5 nm (Pt/C-HT) are considered. X-ray diffraction (XRD), ex situ transmission electron microscopy (TEM) imaging and thin film rotating disc electrode (TF-RDE) along with proprietary high-temperature disc electrode (HT-DE) are used for electrocatalysts inspection. The study shows a clear dependence between the electrochemical surface area (ECSA) loss and the temperature increase during the potentiodynamic accelerated degradation test (ADT). Additionally it is demonstrated that selection of the lower and upper potential limits in ADT protocol plays an important role in ECSA loss. Comparing various results obtained on Pt/C and Pt/C-HT, we show that varying ADT conditions of temperature and different potential windows is crucial for adequate evaluation and stability interpretation of potentially promising novel electrocatalysts and that relatively mild ADT conditions (i.e. 0.4–1.0 V _RHE , RT) can be potentially misleading.

The limited durability of hydrogen fuel cells is one of the main obstacles in their wider adoption as a clean alternative technology for small scale electricity production. The Ostwald ripening of catalyst material is recognized as one of the main unavoidable degradation processes deteriorating the fuel cell performance and shortening its lifetime. The paper systematically studies how the modeling approach towards the electrochemically driven Ostwald ripening in the fuel cell catalyst differs from the classical diffusion driven models and highlights how these differences affect the resulting evolution of particle size distribution. At moderately low electric potential, root-law growth of mean particle size is observed with linear relation between mean particle size and standard deviation of particle size distribution, similar to Lifshitz-Slyozov-Wagner theory, but with broader and less skewed distribution. In case of high electric potential, rapid particle growth regime is observed and qualitatively described by redeposition of platinum from a highly oversaturated solution, revealing the deficiencies of the existing platinum degradation models at describing the Ostwald ripening in the fuel cells at high electric potentials. Several improvements to the established models of platinum degradation in fuel cell catalysts are proposed, aimed at better description of the diffusion processes involved in particle growth due to Ostwald ripening.