| 1. |
- Bultel, Yann, et al.
(författare)
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Investigation of mass transport in gas diffusion layer at the air cathode of a PEMFC
- 2005
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 51:3, s. 474-488
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Tidskriftsartikel (refereegranskat)abstract
- In a polymer electrolyte membrane fuel cell (PEMFC), slowdiffusion in the gas diffusion electrode may induce oxygen depletion when using air at the cathode. This work focuses on the behavior of a single PEMFC built with a Nafion® based MEA and an E-TEK gas diffusion layer and fed at the cathode with nitrogen containing 5, 10 and 20% of oxygen and working at different cell temperatures and relative humidities. The purpose is to apply the experimental impedance technique to cells wherein transport limitations at the cathode are significant. In parallel, a model is proposed to interpret the polarization curves and the impedance diagrams of a single PEMFC. The model accounts for mass transport through the gas diffusion electrode. It allows us to qualitatively analyze the experimental polarization curves and the corresponding impedance spectra and highlights the intra-electrode processes and the influence of the gas diffusion layer.
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| 2. |
- Gode, Peter, et al.
(författare)
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Influence of the composition on the structure and electrochemical characteristics of the PEFC cathode
- 2003
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686 .- 1873-3859. ; 48:28, s. 4175-4187
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Tidskriftsartikel (refereegranskat)abstract
- The influence the composition of the cathode has on its structure and electrochemical performance was investigated for a Nafion content spanning from 10 to 70 wt.%. The cathodes were formed on a Nafion membrane by the spray method and using 20 wt.% Pt on Vulcan (E-TEK). Materials characterisation (SEM, STEM, gas and mercury porosimetry, electron conductivity) and electrochemical characterisation (steady-state polarisation curve, impedance spectroscopy in O-2 and current-pulse measurements in N-2) were performed. The impedance spectra were analysed using our dynamic agglomerate model. The results indicate that the agglomerate model is valid until a Nafion content of about 45 wt.%. Pt/C and Nation are homogeneously mixed for any composition and no Nafion film was observed. The cathodes containing 36-43 wt.% Nation display a single or double Tafel slope behaviour ascribed to diffusion limitations in the agglomerates. At larger Nation content, the agglomerate model can describe the curves only by assuming a diffusion coefficient 3-4 decades smaller than that of gases. At such compositions, the porosity was only 10%. These results were interpreted as a blocking of the pores and a non-percolating pore system for too large Nafion contents.
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| 3. |
- Jaouen, Frédéric, et al.
(författare)
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Adhesive copper films for an air-breathing polymer electrolyte fuel cell
- 2005
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 144:1, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- A design for an air-breathing and passive polymer electrolyte fuel cell is presented. Such a type of fuel cell is in general promising for portable electronics. In the present design, the anode current collector is made of a thin copper foil. The foil is provided with an adhesive and conductive coating, which firstly tightens the hydrogen compartment without mask or clamping pressure, and secondly secures a good electronic contact between the anode backing and the current collector. The cathode comprises a backing, a gold-plated stainless steel mesh and a current collector cut out from a printed circuit board. Three geometries for the cathode current collector were evaluated. Single cells with an active area of 2 cm(2) yielded a peak power of 250-300 MW cm(-2) with air and pure H-2 in a complete passive mode except for the controlled flow of H-2. The cells' response was investigated in steady state and transient modes.
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| 4. |
- Jaouen, Frédéric, 1974-
(författare)
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Electrochemical characterisation of porous cathodes in the polymer electrolyte fuel cell
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer electrolyte fuel cells (PEFC) convert chemicalenergy into electrical energy with higher efficiency thaninternal combustion engines. They are particularly suited fortransportation applications or portable devices owing to theirhigh power density and low operating temperature. The latter ishowever detrimental to the kinetics of electrochemicalreactions and in particular to the reduction of oxygen at thecathode. The latter reaction requires enhancing by the verybest catalyst, today platinum. Even so, the cathode isresponsible for the main loss of voltage in the cell. Moreover,the scarce and expensive nature of platinum craves theoptimisation of its use.The purpose of this thesis was to better understand thefunctioning of the porous cathode in the PEFC. This wasachieved by developing physical models to predict the responseof the cathode to steady-state polarisation, currentinterruption (CI) and electrochemical impedance spectroscopy(EIS), and by comparing these results to experimental ones. Themodels account for the kinetics of the oxygen reduction as wellas for the transport of the reactants throughout the cathode,i.e. diffusion of gases and proton migration. The agglomeratestructure was assumed for the description of the internalstructure of the cathode. The electrochemical experiments wereperformed on electrodes having a surface of 0.5 cm2 using alaboratory fuel cell.The response of the cathode to various electrodecompositions, thickness, oxygen pressure and relative humiditywas experimentally investigated with steady-state polarisation,EIS and CI techniques. It is shown that a content in thecathode of 35-43 wt % of Nafion, the polymer electrolyte, gavethe best performance. Such cathodes display a doubling of theapparent Tafel slope at high current density. In this region,the current is proportional to the cathode thickness and to theoxygen pressure, which, according to the agglomerate model,corresponds to limitation by oxygen diffusion in theagglomerates. The same analysis was made using EIS. Moreover,experimental results showed that the Tafel slope increases fordecreasing relative humidity. For Nafion contents lower than 35wt %, the cathode becomes limited by proton migration too. ForNafion contents larger than 40 wt %, the cathode performance athigh current density decreases again owing to an additionalmass transport. The latter is believed to be oxygen diffusionthroughout the cathode. The activity for oxygen reduction ofcatalysts based on iron acetate adsorbed on a carbon powder andpyrolysed at 900°C in ammonia atmosphere was alsoinvestigated. It was shown that the choice of carbon has atremendous effect. The best catalysts were, on a weight basis,as active as platinum.Keywords:polymer electrolyte fuel cell, cathode, masstransport, porous electrode, modelling, agglomerate model,electrochemical impedance spectroscopy, current interrupt,transient techniques, non-noble catalysts
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| 5. |
- Jaouen, Frédéric, et al.
(författare)
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Transient techniques for investigating mass-transport limitations in gas diffusion electrodes : II. Experimental characterization of the PEFC cathode
- 2003
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 150:12, s. A1711-A1717
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Tidskriftsartikel (refereegranskat)abstract
- The current-interrupt technique and electrochemical impedance spectroscopy were employed in order to study the behavior of a polymer electrolyte fuel cell (PEFC) cathode containing 30 wt % Nafion and 70 wt % Pt/C. The steady-state polarization curves were also recorded. The experimental results were analyzed with help of the mathematical models developed in Part I of this paper. The effect of a varying oxygen pressure and humidity on the dynamic response of the cathode was investigated. The double-layer capacitance, Tafel slope, oxygen solubility, a group containing the effective O-2 diffusion coefficient and agglomerate size, and finally, the effective proton conductivity in the cathode were obtained. The parameter values were reasonable and attest the robustness of the agglomerate model for describing the PEFC cathode. At low humidity, a second, low-frequency loop was observed that was attributed to the membrane behavior.
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| 6. |
- Wijngaart, Wouter van der, et al.
(författare)
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Electrochemical device
- 2005
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Patent (populärvet., debatt m.m.)abstract
- A polymer electrolyte electrochemical device comprising an anode current collector (1), a membrane electrode assembly (2) with anode and cathode gas backings (3, 4), and a cathode current collector (5), wherein the membrane electrode assembly is sealed and attached at least to the anode current collector by adhesive means, thereby creating an anode gas chamber, and optionally attached to the cathode current collector by adhesive means, said adhesive means being electrically conducting or electrically non-conducting. The invention also relates to polymer electrolyte electrochemical device components adapted for use in a single cell electrochemical device and a series arrangement electrochemical device.
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