Sassenage, France
Sassenage, France

Time filter

Source Type

Dubau L.,Joseph Fourier University | Lopez-Haro M.,Joseph Fourier University | Castanheira L.,Joseph Fourier University | Durst J.,Joseph Fourier University | And 6 more authors.
Applied Catalysis B: Environmental | Year: 2013

Long-term (3422h) operation of proton exchange membrane fuel cell in stationary conditions causes two regimes of degradation of the cathode catalytic layer. Firstly, from the beginning of life until the first membrane electrode assembly sampling, at t=1163h, fast degradation of the fresh Pt3Co/C nanoparticles is monitored; classical degradation mechanisms of Pt-based electrocatalysts occur, such as carbon corrosion, crystallite migration, dissolution of the less noble metal (Co), and 3D Ostwald ripening. A second degradation regime sets up from 1163h to 3422h, during which the changes in composition and morphology are slower. At the end of the ageing test, three distinct populations of Pt-Co/C nanoparticles coexist: (i) Pt-Co/C core-shell particles characterized by an alloyed (but depleted, compared to the fresh material) core surrounded by a 3-5 monolayer thick Pt-rich shell, (ii) Pt-Co/C "hollow" particles containing a central cavity surrounded by a Pt-Co shell containing limited amount of Co atoms distributed at the atomic scale and (iii) pure Pt/C "hollow" particles, from which Co dissolution has been completed. Experimental evidences are provided that the Pt-rich phase remains stable, and maintains constant ORR activity over more than 2000h of operation in real PEMFC conditions. © 2013 Elsevier B.V.


Lopez-Haro M.,Joseph Fourier University | Dubau L.,Joseph Fourier University | Guetaz L.,CEA Grenoble | Bayle-Guillemaud P.,Joseph Fourier University | And 6 more authors.
Applied Catalysis B: Environmental | Year: 2014

The oxygen reduction reaction (ORR), which is the cathodic reaction in a proton-exchange membrane fuel cell (PEMFC) and in several other important processes, is a widely studied reaction. From the kinetics viewpoint, Pt is the best electrocatalyst and its activity can be increased upon alloying with a 3d-transition metal (Co, Ni, Fe, Cu). Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy prove that the structural and compositional changes of Pt3Co/C nanoparticles during real-life PEMFC operation are much richer than previously thought from accelerated stress tests. Four different nanostructures are observed after 3422h of operation in stationary mode: Pt, Pt-Co/C "hollow", Pt-Co core-shell and Pt "bulk" nanoparticles. The presence of "hollow" nanoparticles in the aged catalytic layer is accounted for by the nanoscale Kirkendall effect, a vacancy-mediated diffusion mechanism in binary alloys where one species diffuses faster than the other. The oxygen reduction reaction specific activity of the "hollow" nanostructures is 1.5-fold that of the fresh Pt3Co/C cathode catalyst and 3-fold that of Pt/C nanoparticles, thereby offering a new route to synthesize highly active and durable PEMFC electrocatalysts. © 2014 Elsevier B.V.


Dubau L.,Joseph Fourier University | Durst J.,Joseph Fourier University | Maillard F.,Joseph Fourier University | Guetaz L.,CEA Grenoble | And 3 more authors.
Electrochimica Acta | Year: 2011

This paper provides further insights into the degradation mechanisms of nanometer-sized Pt3Co/C particles under various proton-exchange membrane fuel cell (PEMFC) operating conditions. We confirm that Co atoms are continuously depleted from the mother Pt3Co/C electrocatalyst because they can diffuse from the bulk to the surface of the material. The structure of the Pt-Co/C nanoparticles in the long-term is determined by a balance between Co surface segregation and formation of oxygenated species from water splitting. When the PEMFC is operated at high current density (low cathode potential, below the onset of surface oxide formation from water), a steady-state is reached between the rate of Co dissolution at the surface and Co surface segregation. Consequently, Co and Pt atoms remain homogeneously distributed within the Pt-Co/C particles and the thickness of the Pt-shell is maintained to a small value not detectable by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. When the PEMFC is operated at low current density (high cathode potential), the formation of surface oxides from water and the resulting "place-exchange" mechanism enhance the rate of diffusion of Co atoms to the surface. Consequently, the fresh Pt 3Co/C particles form core/shell particles with thick Pt-shells and Co content < 5 at% and, ultimately, "hollow" Pt nanoparticles (Kirkendall effect). To the best of our knowledge, this is the first report on the formation of "hollow" Pt particles in a PEMFC. © 2011 Elsevier Ltd. All rights reserved.


Dubau L.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Maillard F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Chatenet M.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Andre J.,Axane | Rossinot E.,Axane
ECS Transactions | Year: 2010

In this work, we operated a 16-cells stack based on Pt/C anode and Pt 3Co/C cathode under H2/air at constant current (j = 0.6 A cm-2) for 1124 h. The MEA were characterized with special emphasis on the cathode electrocatalyst, using physical, chemical and electrochemical techniques after different life stages: as received (fresh: 0 h), conditioned (17 h) and aged for 504 or 1124 h. The fresh Pt3Co/C cathode catalyst is not stable during PEMFC operation and suffers compositional changes. In particular, the dissolution of Co atoms at the surface yields to the formation of a Pt-shell/Pt-Co alloy core structure. The high electrochemical potential of the cathode induces formation of surface oxides and drives continuous Co surface segregation. The dissolution of Co atoms at the surface increases the affinity of the surface to oxygenated and hydrogenated species and renders the electrocatalyst less active towards the ORR. ©The Electrochemical Society.


Danerol A.S.,University of Savoy | Bas C.,University of Savoy | Flandin L.,University of Savoy | Claude E.,AXANE | Alberola N.D.,University of Savoy
Journal of Power Sources | Year: 2011

The changes in properties within membrane electrode assemblies (MEAs) aged in a stack functioning at constant-power operation (0.12 W cm-2) for several durations (0, 347, 892, and 1397 h) were characterized. An important effort was placed into better understanding interfaces. Two tests were thus developed to investigate the changes in each active layer/membrane interface. Both techniques demonstrated that the mechanical bounding of both cathode and anode to the polymer membrane improve with the functioning time in fuel cell. This phenomenon was further attributed to Pt dissolution and diffusion/precipitation within the polymer membrane and to a diffusion/crystallization of the binding agent in the vicinity of the electrode/membrane interfaces. © 2010 Elsevier B.V. All rights reserved.


Bas C.,University of Savoy | Flandin L.,University of Savoy | Danerol A.-S.,University of Savoy | Claude E.,Axane | And 2 more authors.
Journal of Applied Polymer Science | Year: 2010

Changes in a perfluorosulfonated acid polymer membrane in membrane electrode assemblies were studied after different times under stationary conditions in fuel cells. A large series of characterizations demonstrated changes in the morphology, mechanical behavior, and thermal stability upon aging. Overall, the membrane evolution could be mainly attributed to both chemical degradation and cationic contamination. The reduction in the membrane thickness, detected by scanning electron microscopy, was ascribed to a radical unzipping mechanism and polymer chain erosion after 900 h in service. An additional monotonic decrease in the number of CtertiaryF groups was observed even at 400 h. In parallel, membranes were cation-contaminated, and this led to drastic changes in the thermal and mechanical properties in the first stage of fuel-cell operation. The pollution cations were shown to have Lewis acid strengths close to 0.25 and thus strongly interacted with sulfonate anions of the membrane. The kinetic dependence of these membrane modifications and the influence of the platinum band were also examined. © 2010 Wiley Periodicals, Inc.


Dubau L.,Joseph Fourier University | Durst J.,Joseph Fourier University | Maillard F.,Joseph Fourier University | Chatenet M.,Joseph Fourier University | And 2 more authors.
Fuel Cells | Year: 2012

In this study, we investigated the long-term morphological and chemical changes of PEMFC cathode materials, with a special focus on the homogeneity of aging in different operating conditions (stationary or intermittent). The spatially-resolved physico-chemical analyses, performed at the cathode inlet/outlet region of the membrane electrode assembly, put in evidence that the cathode inlet ages much more rapidly than the cathode outlet in counter-flow mode, this effect being exacerbated at high cell current. The rationale for such observation is the existence of heterogeneities of local current density, essentially caused by the depletion in air partial pressure and the increase in water content along the gas-channel. We also evidenced heterogeneities of aging through the catalytic layer (CL). These heterogeneities are explained by the fact that Pt z+ ions produced by the corrosion of the Pt-Co/C nanoparticles are evacuated by the produced water exiting the CL [at the gas-diffusion layer (GDL)|CL interface] or consumed by H 2 crossing-over from the anode through the cathode [at the CL|proton-exchange membrane (PEM) interface], resulting in the formation of the so-called "platinum-band" in the PEM. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Maillard F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Dubau L.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Durst J.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Chatenet M.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | And 2 more authors.
Electrochemistry Communications | Year: 2010

Pt3Co/C electrocatalysts are not stable when operated in real PEMFC conditions but face variations of their chemical composition. The latter signs that Co atoms can segregate from the bulk to the surface of the nanoparticles, which we believe is activated by the formation of surface oxides and the leaching of Co at the surface. Consequently, the alloyed Pt 3Co/C nanoparticles slowly evolve towards Pt shell/Pt-Co alloy core structures with depleted Co content and a Pt-enriched shell. © 2010 Elsevier B.V. All rights reserved.


Dubau L.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Maillard F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Chatenet M.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Andre J.,Axane | Rossinot E.,Axane
Electrochimica Acta | Year: 2010

This study bridges the structure/composition of Pt-Co/C nanoparticles with their surface reactivity and their electrocatalytic activity. We show that Pt3Co/C nanoparticles are not stable during PEMFC operation (H 2/air; j = 0.6 A cm-2, T = 70 °C) but suffer compositional changes at the nanoscale. In the first hours of operation, the dissolution of Co atoms at their surface yields to the formation of a Pt-enriched shell covering a Pt-Co alloy core ("Pt-skeleton") and increases the affinity of the surface to oxygenated and hydrogenated species. This structure does not ensure stability in PEMFC conditions but is rather a first step towards the formation of "Pt-shell/Pt-Co alloy core" structures with depleted Co content. In these operating conditions, the Pt-Co/C specific activity for the ORR varies linearly with the fraction of Co alloyed to Pt present in the core and is severely depreciated (ca. -50%) after 1124 h of operation. This is attributed to: (i) the decrease of both the strain and the ligand effect of Co atoms contained in the core (ii) the changes in the surface structure of the electrocatalyst (formation of a multilayer-thick Pt shell) and (iii) the relaxation of the Pt surface atoms. © 2010 Elsevier Ltd. All rights reserved.


Trademark
Axane | Date: 2011-06-07

Fuel cell system for generating electricity, in particular for lighting and sound recording during the filming of cinema. Installation, maintenance, servicing, and repair of fuel cell electric generators. Rental of fuel cell electric generators.

Loading Axane collaborators
Loading Axane collaborators