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Roth J.,Electrochemistry Laboratory | Zurbrugg M.,Electrochemistry Laboratory | Irvine S.,Paul Scherrer Institute | Marone F.,Paul Scherrer Institute | And 3 more authors.
ECS Transactions | Year: 2013

Starting from subfreezing temperatures presents a challenge for PEFC since ice may form in the gas flow channel, gas diffusion layer and catalyst layer and restrict the gas transport. Under nonisothermal conditions, a start-up is successful if the cell temperature rises above 0 °C before freezing occurs. Under isothermal conditions below 0 °C cells operate for a certain time followed by a sudden drop in power. The distribution of liquid/solid water during an isothermal start at subfreezing temperatures is quantitatively mapped by means of X-ray tomographic microscopy to improve understanding the circumstances at the phase transition and its effects on gas diffusion. Evidence was found that the produced water is in supercooled state at -10 °C initially and the drop of power is associated with freezing of the water in the cell at a GDL saturation of 20 to 30%. © The Electrochemical Society.


Asgari M.,Electrochemistry Laboratory | Maragheh M.G.,Electrochemistry Laboratory | Davarkhah R.,Electrochemistry Laboratory | Lohrasbi E.,Electrochemistry Laboratory | Golikand A.N.,Electrochemistry Laboratory
Electrochimica Acta | Year: 2012

In this work, Ni-Co alloy coating on the surface of glassy carbon (GC) electrode was performed by cyclic voltammetry. The results showed that the deposition of Ni-Co is an anomalous process. The deposition bath was prepared according to the metal ion Ni/Co ratio of 4:1 using NiSO 4· 7H 2O and CoSO 4·8H 2O, and the total concentration of all solutions was 40.0 mM. The pH of the bath solution was adjusted at 2.0 using boric acid at room temperature. The modified electrode was conditioned by potential recycling in a potential range of 100-700 mV (vs. Ag/AgCl) by cyclic voltammetric method in an alkaline solution. The Ni-Co modified electrode showed a higher activity towards methanol oxidation in the Ni (III) and Co (IV) oxidation states. Cyclic voltammetry was used for the electrochemical characterization of the Ni-Co modified electrode and the mechanism of methanol oxidation is proposed. The result of double steps chronoamperometry shows that the methanol electrooxidation is an irreversible reaction. Moreover, the effects of various parameters such as mole ratio of Ni-Co in the alloy in modification step, potential scan rate, methanol concentration and solution temperature on the electro-oxidation of methanol have also been investigated. © 2011 Elsevier Ltd. All Rights Reserved.


Yousef U.S.,Electrochemistry Laboratory | Ragab A.Z.-E.,Electrochemistry Laboratory | Abdel-Azzem M.,Electrochemistry Laboratory
Electrochimica Acta | Year: 2010

Electrooxidative polymerization of the 1-amino-5,6,7,8-tetrahydronaphthalene (ATHN) monomer on a glassy carbon (GC) electrode was carried out in an acetonitrile solution containing LiClO4 using consecutive multisweep cyclic voltammetry and controlled potential electrolysis techniques. The factors that affected the film formation, such as monomer concentration, number of sweeping cycles, sweep rate and limits of potential cycling were investigated in detail. The obtained modified electrode was active only in acidic solutions, and its activity was found to be pH dependent. The effects of pH and temperature on the obtained modified electrode were studied. The obtained modified electrode has been found to improve the electrochemical reversibility and decrease the overpotential of hydroquinone. © 2009 Elsevier Ltd. All rights reserved.


Schneider I.A.,Electrochemistry Laboratory | Von Dahlen S.,Electrochemistry Laboratory | Bayer M.H.,Electrochemistry Laboratory | Scherer G.G.,Electrochemistry Laboratory | Wokaun A.,PSI
ECS Transactions | Year: 2010

An experimental approach for submillimeter resolved current distribution measurements in polymer electrolyte fuel cells (PEFCs) is presented. The approach is employed for locally resolved in situ diagnostics in channel and land areas. Thereby, we focus on laterally resolved transient techniques. The results of ac impedance spectroscopy, voltage step, and cyclic voltammetry experiments demonstrate that phenomena, which occur as a result of inhomogeneous operation of PEFCs in the down the channel direction typically on a length scale of tens of centimeters, have their counterpart on the millimeter scale of channels and ribs in the direction perpendicular to the flow channels. Both must be treated with same attention. ©The Electrochemical Society.


Schwanitz B.,Electrochemistry Laboratory | Rabis A.,Electrochemistry Laboratory | Horisberger M.,Paul Scherrer Institute | Scherer G.G.,Electrochemistry Laboratory | Schmidt T.J.,Electrochemistry Laboratory
Chimia | Year: 2012

The level of Pt loadings in polymer electrolyte fuel cells (PEFC) is still one of the main hindrances for implementation of PEFCs into the market. Therefore, new catalyst and electrode preparation methods such as sputtering are of current interest, because they allow thin film production and have many cost saving advantages for electrode preparation. This paper summarises some of the most important studies done for sputtered PEFCs, including non carbon supported electrodes. Furthermore, it will be shown that an understanding of the main morphological differences between sputtered and ink-based electrodes is crucial for a better understanding of the resulting fuel cell performance. Especially, the electrochemical surface area (ECSA) plays a key role for a further increase in PEFC performance of sputtered electrodes. The higher surface specific activities ik,spec of sputtered compared to ink-based electrodes will be discussed as advantage of the thin film formation. The socalled particle size effect, known in literature for several years, will be discussed as reason for the higher i k,spec of sputtered electrodes. Therefore, a model system on a rotating disc electrode (RDE) was studied. For sputtered PEFC cathodes Pt loadings were lowered to 100 μg Pt/cm 2, yet with severe performance losses compared to ink-based electrodes. Still, for Pt sputtered electrodes on a carbon support structure remarkably high current densities of 0.46 A/cm 2 at 0.6 V could be achieved. © Schweizerische Chemische Gesellschaft.


Shamsipur M.,Razi University | Asgari M.,Tarbiat Modares University | Maragheh M.G.,Electrochemistry Laboratory | Moosavi-Movahedi A.A.,University of Tehran
Bioelectrochemistry | Year: 2012

A robust and effective nanocomposite film-glassy carbon modified electrode based on multi-walled carbon nanotubes and a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate was prepared by a layer-by-layer self-assembly method. The fabricated modified electrode was used as a novel impedimetric catalase nanobiosensor for the determination of H 2O 2. Direct electron transfer and electrocatalysis of catalase were fully investigated. The results suggested that catalase could be firmly adsorbed at the modified electrode. A pair of quasi-reversible redox peaks of catalase was observed in a 0.20M degassed phosphate buffer solution of pH 7.0. The nanocomposite film showed a pronounced increase in direct electron transfer between catalase and the electrode. The immobilized catalase exhibited an excellent electrocatalytic activity towards the reduction of H 2O 2. The electrochemical impedance spectroscopy measurements revealed that the charge transfer resistance decreases significantly after enzymatic reaction with hydrogen peroxide, so that the prepared modified electrode can be used for the detection of ultra traces of H 2O 2 (5-1700nM). © 2011 Elsevier B.V.


Asgari M.,Electrochemistry Laboratory | Maragheh M.G.,Electrochemistry Laboratory | Davarkhah R.,Electrochemistry Laboratory | Lohrasbi E.,Electrochemistry Laboratory
Journal of the Electrochemical Society | Year: 2011

The preparation of multi-walled carbon nanotubes-NiO nanoparticles composites (MWCNT-NiO) and their application as modifier for methanol electrooxidation in NaOH are presented. Nickel oxide nanoparticles were accumulated on multi-walled carbon nanotubes (MWCNT) by pulsed potential electrodeposition. The structure and nature of the GC/MWCNTs/NiO were characterized by Transmission electron microscopy (TEM), the results indicated that NiO nanoparticles were homogeneously electrodeposited on the surfaces of MWCNT. Also, the electrochemical behavior of carbon nanotubes-NiO nanoparticles composites in the alkaline solutions of methanol has been studied by cyclic voltammetry, and electrochemical impedance spectroscopy. The observed peak on the potentiodynamic curve for MWCNT-NiO composite electrode in alkaline solutions of methanol is observed which is ascribed to the methanol oxidation in alkaline medium. The achieved results obtained, are discussed for the MWCNT-NiO composites for the catalytic electrodes of fuel cells. © 2011 The Electrochemical Society.


PubMed | Electrochemistry Laboratory
Type: Journal Article | Journal: Chimia | Year: 2012

The level of Pt loadings in polymer electrolyte fuel cells (PEFC) is still one of the main hindrances for implementation of PEFCs into the market. Therefore, new catalyst and electrode preparation methods such as sputtering are of current interest, because they allow thin film production and have many cost saving advantages for electrode preparation. This paper summarises some of the most important studies done for sputtered PEFCs, including non carbon supported electrodes. Furthermore, it will be shown that an understanding of the main morphological differences between sputtered and ink-based electrodes is crucial for a better understanding of the resulting fuel cell performance. Especially, the electrochemical surface area (ECSA) plays a key role for a further increase in PEFC performance of sputtered electrodes. The higher surface specific activities i(k,spec) of sputtered compared to ink-based electrodes will be discussed as advantage of the thin film formation. The so- called particle size effect, known in literature for several years, will be discussed as reason for the higher i(k,spec) of sputtered electrodes. Therefore, a model system on a rotating disc electrode (RDE) was studied. For sputtered PEFC cathodes Pt loadings were lowered to 100 g(Pt)/cm(2), yet with severe performance losses compared to ink-based electrodes. Still, for Pt sputtered electrodes on a carbon support structure remarkably high current densities of 0.46 A/cm(2) at 0.6 V could be achieved.

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