CNRS Physical Eletrochemistry Materials and Interfaces Lab

Grenoble, France

CNRS Physical Eletrochemistry Materials and Interfaces Lab

Grenoble, France
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Oury A.,French National Solar Energy Institute | Kirchev A.,French National Solar Energy Institute | Bultel Y.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Electrochimica Acta | Year: 2012

This work examines the oxygen evolution reaction (OER) taking place on α-PbO 2 electrode in methanesulfonic acid (MSA) medium and in sulphuric acid as a comparison, by means of cyclic voltammetry (CVA) and electrochemical impedance spectroscopy (EIS), for soluble lead acid flow battery applications. The influence of MSA concentration on OER is studied. EIS measurements highlighted the impact of the hydrated lead dioxide layer upon decreasing MSA or sulphuric acid concentration. The evolution of the Tafel curves plotted from EIS measurements and quasi-stationary currents while varying acid concentration was interpreted in the light of this hydrated layer which could enhance the electrocatalytic activity when it is thin, and on the contrary act as an electronic barrier when growing for low acid concentration. Both EIS and CVA revealed that OER on lead dioxide is less favoured in MSA than in sulphuric acid. It is finally concluded that a high-concentrated MSA electrolyte is better for lead acid flow battery application in terms of oxygen evolution. © 2011 Elsevier Ltd. All rights reserved.


Maillard F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Bonnefont A.,CNRS Strasbourg Institute of Chemistry | Micoud F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Electrochemistry Communications | Year: 2011

In this study, we investigate the role of Pt in the corrosion of carbon by Fourier-transformed infrared spectroscopy coupled in situ with electrochemical measurements. We confirm that the carbon corrosion rate is strongly enhanced in the presence of Pt and shed light on the reaction mechanisms at both anode and cathode potentials. It is shown that carbon surface oxide species (phenol, ether, carboxylic and carbonyl groups), formed at low electrode potential E < 0.60 V vs. RHE, spillover back from the carbon support to the Pt nanoparticles, where they are converted into CO and then slowly oxidized into CO2. At higher electrode potential E > 0.60 V vs. RHE, oxygenated species resulting from water splitting on Pt facilitate the removal of these carbon surface oxides species yielding increased kinetics for carbon corrosion. © 2011 Elsevier B.V. All Rights Reserved.


Martinelli A.,Chalmers University of Technology | Marechal M.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Ostlund A.,Chalmers University of Technology | Cambedouzou J.,CNRS Marcoule Institute for Separative Chemistry
Physical Chemistry Chemical Physics | Year: 2013

We report on how the local structure and the diffusional motion change upon increasing the alkyl chain length in 1-alkyl-3-methylimidazolium cation ionic liquids. This study has been performed by combining pulse field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and small angle X-ray scattering (SAXS) experiments. The cationic side chain length varies from ethyl (n = 2) to hexadodecyl (n = 16), while the anion is always bis(trifluoromethanesulfonyl) imide (TFSI). We find that the self-diffusivity of the individual ionic species is correlated to the local structure in the corresponding ionic liquid, namely the nano-segregation into polar and non-polar domains. In agreement with previous results, we observe that for relatively short alkyl chains the cations diffuse faster than the anions; however we also note that this difference becomes less evident for longer alkyl chains and a cross-over is identified at n ≈ 8 with the anions diffusing faster than the cations. Our results indicate that this controversial behavior can be rationalized in terms of different types of cation-cation and anion-anion orderings, as revealed by a detailed analysis of the correlation lengths and their dispersion curves obtained from SAXS data. We also discuss the validity of the Stokes-Einstein relation for these ionic liquids and the evolution of the extrapolated cationic radius that was found to depend non-strictly linearly on n, in agreement with the cation-cation correlation lengths. © 2013 the Owner Societies.


Carral C.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Mele P.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
International Journal of Hydrogen Energy | Year: 2014

A finite element model is developed to investigate the influence of the assembly phase of proton exchange membrane fuel cell (PEMFC) stacks on the mechanical state of the active layer (MEAs). Validated by experimental measurements, this model offers the possibility to analyze the influence of different parameters through the use of a complete parametric set, such as the number of cells and their position in the stack. The simulations show that a better uniformity of the MEA compression is obtained with the greatest number of cells, and at the center of the stack. The finite element analysis (FEA) is finally found to be an effective tool to show the influence of the assembly phase on the performance of PEMFCs, and will help the designer to adapt the future generations of stack to ensure the uniformity of the MEA mechanical strain. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Nonlinearity effects of electrochemical systems kinetics on impedance measurements are re-examined in the low-frequency (LF) domain through symbolic manipulation and numerical computation performed with Mathematica. It is a new approach to some problems not yet completely resolved in electrochemical impedance spectroscopy despite a number of publications on this subject in the specialized literature. This article is focused on electrochemical systems governed by Tafel kinetics under steady-state conditions, so-called Tafelian systems below, and perturbed by a sinusoidal variation of electrode potential vs. time, at low frequency. First, harmonic analysis of the system response to sinusoidal perturbation of potential with negligible Ohmic drop effects is dealt with. Next, the combined effects of Tafel kinetics and Ohmic drop are thoroughly examined. The current-potential response at low frequency is modelled using the Lambert W-function. New formulations are derived for the nonlinear polarization resistance of Tafelian systems in the presence of Ohmic drop. Closed-form or infinite-series formulations are derived for the amplitudes of fundamental and harmonic components of periodic current. Finally, the validity condition for impedance measurements carried out in the LF domain is derived for Tafelian systems. © 2012 Elsevier B.V. All rights reserved.


Neyertz S.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Brown D.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Journal of Membrane Science | Year: 2014

Changing a glassy polyimide dianhydride-diamine bond location from para to meta has been shown experimentally to lead to significant decreases in gas permeabilities. This work is aimed at comparing a fully-atomistic molecular model of a meta-linked 6FDA-6FmDA polyimide membrane to its para-linked 6FDA-6FpDA isomer using large-scale molecular dynamics simulations (MD). The effects of structural isomerism on the early stages of CO2 sorption and matrix plasticization are also assessed. Both isomers are close in densities, but the meta-chains are more coiled than the para-chains, their void-space is slightly smaller and their mobility is lower. The higher resistance of the meta-matrix to localized chain motions leads to a better conservation of its cohesion and a reduced volume dilation upon CO2 entry into the membranes. In agreement with its larger dilating capacity, the gas uptake is always higher in the para isomer. The concave behavior of the sorption curves compares favorably with experimental data, except for the highest-pressure system which exhibits a quasi-supercritical behavior for CO2. However, in all cases, swelling is associated to local relaxations of the matrices rather than to large changes in the structures, while glassy chain mobility remains fairly restricted. Gas mobility is directly correlated to the underlying mobility of the matrices and, as such, is slower in the meta than in the para isomer. © 2014 Elsevier B.V.


Montella C.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Journal of Electroanalytical Chemistry | Year: 2012

This article deals with the influence of interfacial CPE (constant phase element) behaviour on linear scan voltammograms (LSV) and cyclic voltammograms (CV). Theoretical investigation is carried out using the generalised Mittag-Leffler function which arises naturally in the solution of fractional order integral or differential equations. First, ohmic drop and CPE effects are analysed in the absence of electrochemical reaction through the closed-form expression of current vs. time. Next, the combined effects of ohmic drop, CPE and faradaic processes are modelled using the integral equation approach. Finally, the example of one-step electrochemical reaction, investigated under semi-infinite linear diffusion conditions, is dealt with for illustration of the calculation procedure. © 2011 Elsevier B.V. All rights reserved.


Neyertz S.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Brown D.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Macromolecules | Year: 2013

A series of large-scale molecular dynamics (MD) simulations of CO 2 transport in a fully atomistic ∼50000-atom fluorinated 6FDA-6FpDA polyimide membrane were carried out under six different conditions of applied external gas pressure in order to assess the uptake mechanisms of the penetrant at the glassy polymer interface. CO2-induced volume dilation was found to occur immediately with a progressive shift of the interface location toward larger values associated with a widening of the interface and a decrease in density. However, it only leads to limited structural relaxations of the matrices and as such, the corresponding increase in mobility is small. Void-space and excess chemical potential analyses show that the holes within the matrix are getting larger as sorption proceeds, but that they are immediately occupied by penetrant molecules. The only way to accommodate more penetrant is to further swell the polymer matrix. The concave behavior of the sorption curves is well reproduced by the models and compares favorably with experimental data, except for the highest-pressure system which is in a different regime and exhibits a quasi-supercritical behavior for CO 2. In all cases, the penetrants first undergo a rapid adsorption at the polymer surface. This is followed by a slower uptake mode, with the time-dependent diffusion coefficient being only accessible for short time-intervals because of the moving boundaries. All trajectories display the oscillations in voids and occasional jumps mechanism, and no transitions to the paths characteristic of liquid-like diffusion were seen, even in the most swollen systems. © 2013 American Chemical Society.


Zhao Z.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Dubau L.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Maillard F.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Journal of Power Sources | Year: 2012

In this study, we made use of structural markers to gain more insights into the structural stability of commercial carbon-supported Pt electrocatalysts under oxidizing, inert and reducing atmospheres. The materials were characterized by electron microscopy and electrochemical techniques in the fresh state and after various aging conditions. The results show that Pt nanoparticles supported on Vulcan XC72 are not immobile but prone to agglomerate during potential sweeping in the presence of hydrogen (H 2), methanol (CH 3OH), and carbon monoxide (CO). The migration rate of the Pt crystallites is the largest in CO-containing solution and decreases in the order CO > CH 3OH > H 2. We postulate that the morphological changes of the Pt/C nanoparticles are related to the reduction of the oxygen-bearing carbon surface groups strongly interacting with the Pt metal phase. © 2012 Elsevier B.V. All rights reserved.


Marinha D.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Dessemond L.,CNRS Physical Eletrochemistry Materials and Interfaces Lab | Djurado E.,CNRS Physical Eletrochemistry Materials and Interfaces Lab
Journal of Power Sources | Year: 2012

The oxygen reduction reaction of La0.6Sr0.4Co 0.2Fe0.8O3-δ (LSCF) cathodes deposited by Electrostatic Spray Deposition (ESD) onto dense Ce0.9Gd 0.1O2-δ (CGO) electrolytes was characterized by means of impedance spectroscopy measurements. Three cathodes with distinct morphologies and surface areas were prepared. Impedance measurements were performed at temperatures between 450 and 600 °C, at 50 °C steps. At each temperature, impedance measurements were performed at five different oxygen partial pressures (pO2), between ∼10-4 and 1 atm. This approach permitted a systematic evaluation of the influence of microstructure, temperature and pO2 on the electrochemical behavior of the cathodes. Up to three contributions were identified in the high (HF), medium (MF) and low frequency (LF) ranges. The LF response displays the strongest dependence on oxygen partial pressure with corresponding resistance and capacitance values increasing with decreasing pO2. Contrarily, the resistance associated with the HF response remained practically constant with changing pO2, while a slight dependence was found for the MF response. The analysis provides support to the assignment of the HF, MF and LF contributions respectively to the ionic transfer at the cathode/electrolyte interface, bulk diffusion of oxygen species and oxygen surface exchange at pO2>10-2atm. At lower pO2, an increasing contribution of oxygen gas-phase diffusion with temperature, evidenced by the LF response, was suggested. © 2011 Elsevier B.V. All rights reserved.

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