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Several characterization techniques were performed on a proton exchange membrane fuel cell (PEMFC) to relate the performance degradation induced by the membrane-targeted accelerated stress test (AST) to the evolution of electrochemical and physical properties of the electrode. This works investigated the ionomer structure and the proton transport properties. Electron microscopy and small angle neutron scattering analysis provided access to the electrode’s nanoscale structure, the distribution of the platinum particle size, the structure of the 2–3 nm thick ionomer film, as well as the location of the water uptake by the electrode. A newly-developed technique using proton desorption under diluted O2allows to distinguish effectively used active sites for oxygen reduction reaction. Proton transport and dioxygen diffusivity properties were measured using impedance spectroscopy and limiting current technique respectively. The Membrane-AST leads to an increase in the water uptake of the electrode due to a modification of the global structure of the electrode, a reduced platinum surface area, and corrosion of carbon particles. However, it does not alter the ionomer structure. The decrease in performance is partially attributed to the increase in proton resistivity, but mainly due to the limitation of dioxygen transport fostered by the electrode structure modifications.

This study shows that the modifications in structure and composition of Pt3Co/C nanoparticles during real life PEMFC operation (3422 hours of operation at T= 70 °C under H2/air) is much richer than previously thought from accelerated stress tests. Using aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy, we show that Co atoms are continuously dissolved from the mother electrocatalyst, and that three different metal nanostructures emerge during PEMFC operation: (i) Pt-Co/C core-shell nanoparticles characterized by an alloyed core surrounded by a thick Pt-rich shell, (ii) Pt-Co/C “hollow” nanoparticles and (iii) pure Pt/C “hollow” nanoparticles, from which Co dissolution has been completed. The high surface area carbon support is not stable either, its less organized domains being preferentially corroded, a fast kinetics process that is followed by slower corrosion of its graphitic regions.

In this study, we investigate “through-plane” heterogeneities of aging of a Pt3Co/C cathode electrocatalyst aged at I= 20 A or 50 A in a 16 cell proton-exchange membrane fuel cell (PEMFC) stack. Morphological and structural markers of degradation such as the mean nanoparticle size, the degree of agglomeration and the nanostructure of the Pt3Co/C nanoparticles provide evidence that the electrocatalyst degradation is (i) more pronounced close to the proton-exchange membrane (rationalized by different local/electrochemical environments) and (ii) organized in spatially-localized areas, following the incomplete utilization of the cathode electrocatalyst under the dynamic operation conditions of the PEMFC.

In this work, we investigated through-the-plane heterogeneities of an ultramicrotomed MEA aged at constant current density j = 0.24 A cm-2 in a 16 cell stack for t = 1341 h. We used structural markers to unveil the physical and chemical changes occurring at both the GDL | CL and at the CL | PEM interfaces. We evidenced that the degradation of the cathode catalytic layer is more pronounced close to the PEM than close to the GDL. Spatially-localized heterogeneities of ageing are discussed in the frame of different chemical/electrochemical environments as well as incomplete utilization of the cathodic electrocatalyst under PEMFC operation.

Abstract not Available.

In this paper, we present experimental results on the preparation and the electrochemical characterization of PtxCoyelectrocatalytic particles with homogeneous composition, modeled by Franco et al. [ J. Electrochem. Soc. , 156 , B410 (2009) ]. Preparation is made through the direct liquid injection metallorganic chemical vapor deposition technique previously developed at CEA, and electrochemical analysis is carried out by using a rotating disk electrode and membrane-assembled gas diffusion electrode. Degradation structural changes are characterized by using transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Optimal Co compositions are identified for better oxygen reduction reaction activity and durability, validating the modeling studies.

In this article, we focus on the understanding of the PtxCoyelectrocatalysts degradation in polymer electrolyte fuel cell (PEFC) environments. A multiscale atomistic/kinetic model is derived providing mechanistic insights on the impact of the nanostructure and operating conditions on PtxCoynanoparticles durability. On the basis of ab initio (AI) data, we identify favorable pathways of the oxygen reduction reaction (ORR) on PtxCoynanoparticles and of the competitive Pt–Co dissolution in acidic media. The derived AI kinetics is coupled to a description of the atomic reorganization at the nanoparticle level as a function of the cumulated Pt and Co mass losses. This nanoscale model is coupled with a transport microscale model of charges and O2through a PEFC cathode, and simulation sensitivity studies to operating conditions and initial compositions/morphologies are performed and complimented by microstructural and electrochemical characterizations carried out on aging direct liquid injection metallorganic chemical vapor deposition elaborated model electrodes detailed in our experimental companion paper.