[Show abstract][Hide abstract] ABSTRACT: In this study, soluble lead/methanesulfonic acid flow cells comprising a 3-D honeycomb-shaped positive electrode sandwiched between two planar negative electrodes are tested under galvanostatic cycling. Two types of materials are used for the honeycomb: homemade vitreous carbon/carbon composite and graphite. The cells comprising the C/C composite substrate shows a poor cyclability with coulombic and energy efficiencies below 80% and 50%, respectively, as well as a very limited lifetime. After a few tens of cycles, the cells cannot be discharged any longer due to the emergence of overvoltages associated with the passivation of the positive electrode in the discharged states. Using the graphite-based electrode, the cyclability is considerably improved: efficiencies of 95% in charge and 75% in energy are obtained, a hundred of cycles can be achieved and no passivation is observed. The cycle life of the cell is, however, limited by lead dendrite-like formation at the negative plates. Finally, this study shows that the incorporation of fluoride ions into the electrolyte improves greatly the adhesion of PbO2 on the positive electrode surface upon cycling.
Journal of Power Sources 10/2014; 264:22–29. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by Internal Reforming within the SOFC anode. To cope with carbon formation, a new SOFC cell configuration combining a catalyst layer with a classical anode was developed. The rate of the CH4 consumption in the catalyst layer (Ir-CGO) was determined experimentally for small values of steam to carbon ratios. This paper proposes a modeling and a simulation, using the CFD-Ace software package, of the behavior of a SOFC operated in Gradual Internal Reforming (GIR) conditions. This model of SOFC takes into account the kinetics of the steam reforming reaction in the catalyst layer in order to assess the influence of the steam to carbon ratio and the cell polarisation. Because the risk of carbon formation is greater under GIR operation, a detailed thermodynamic analysis was carried out. Thermodynamic equilibrium calculations allowed us to predict the conditions of carbon formation occurrence.
The Canadian Journal of Chemical Engineering 10/2014; · 1.00 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Further analysis of EIS provides valuable information about reliability and aging of the systems, namely to diagnose water flooding the electrode or membrane drying for Proton Exchange Membrane Fuel Cells (PEMFC). The aim of this study is to propose an electrochemical parameter fitting algorithm. A careful study of the electrochemical kinetics laws allowed us to demonstrate that, as long as both electrodes follow a Tafel behavior, the cathode and anode active layer resistances are strongly correlated. This correlation obviously removes a liberty degree in the model and allow an accurate fitting of the utilized model's electrochemical parameters of our PEMFC stack EIS. The reduced number of liberty degrees eases the convergence of the solution of the model. This algorithm was successfully implemented on different PEMFC stacks technology to investigate the impact of water flooding and the operating points.
[Show abstract][Hide abstract] ABSTRACT: A novel reactor design is proposed for the soluble lead-acid flow
battery (SLFB), in which a three-dimensional honeycomb-shaped positive
PbO2-electrode is sandwiched between two planar negative
electrodes. A two-dimensional stationary model is developed to predict
the electrochemical behaviour of the cell, especially the current
distribution over the positive structure and the cell voltage, as a
function of the honeycomb dimensions and the electrolyte composition.
The model includes several experimentally-based parameters measured over
a wide range of electrolyte compositions. The results show that the
positive current distribution is almost entirely determined by
geometrical effects, with little influence from the hydrodynamic. It is
also suggested that an increase in the electrolyte acidity diminishes
the overvoltage during discharge but leads at the same time to a more
heterogeneous reaction rate distribution on account of the faster
kinetics of PbO2 dissolution. Finally, the cycling of
experimental mono-cells is performed and the voltage response is in
fairly good accordance with the model predictions.
Journal of Power Sources 01/2014; · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: For electric vehicle (EV) or hybrid EV (HEV) development and integration of renewables in electrical networks, battery monitoring systems have to be more and more precise to take into account the state-of-charge and the dynamic behavior of the battery. Some non-integer order models of electrochemical batteries have been proposed in literacy with a good accuracy and a low number of parameters in the frequential domain. Nevertheless, time simulation of such models required to approximate this non-integer order system by an equivalent high integer order model. An adapted algorithm is then proposed in this article to simulate the non-integer order model without any approximation, thanks to the construction of a 3-order generalized state-space system. This algorithm is applied and validated on a 2.3 A.h Li-ion battery.
Communications in Nonlinear Science and Numerical Simulation 06/2013; 18(6):1454–1462. · 2.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper presents a new non invasive technique for fuel cell diagnosis. The method relies on the measurements of the magnetic field signature generated by a working fuel cell. Knowing the relationship between currents and magnetic field, it is possible to estimate the current density by solving an inverse problem. This problem being ill-posed, original current and sensors basis are proposed to improve the reconstruction process. The experimental set-up remains simple, based on few fixed sensors and shows a good efficiency.
IEEE Transactions on Magnetics 05/2013; 49(5):1925-1928. · 1.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Proton exchange membrane fuel cell (PEMFC) requires a careful management of the heat distribution inside the stack. The proton exchange membrane is the most sensitive element of this thermal management and it must operate under specific conditions in order to increase the lifetime and also the output power of the fuel cell. These last decades, the enhancement of the output power of the PEMFC has led the manufacturers to greatly improve the heat transfer effectiveness for cooling such systems. In addition, homogenizing the bipolar plate temperature increases the lifetime of the system by limiting the occurrence of strong thermal gradients. In this context, using a fluid in boiling conditions to cool down the PEMFC seems to be very suitable for this purpose. In order to compare the thermal performances between a coolant used in single-phase flow or in boiling flow conditions, we have built an experimental set-up allowing the investigation of cooling flows for these two conditions. Moreover, the geometry of the cooling channels is one of the key parameters which allows the improvement of the thermal performances. Indeed, the size or the aspect ratio of these channels could be designed in order to decrease the thermal system response. The sizing of the fuel cell cooling system is of paramount importance in boiling flow conditions because it can modify, not only the pressure losses along the channel and the heat transfer coefficient like in a single-phase flow but also, the onset of nucleate boiling (ONB) and the dryout point or critical heat flux (CHF). Thus, in order to understand some heat transfer mechanisms, which are geometry-dependent, a parametric study was completed by considering flows in four different rectangular channels. Finally, this study allows a better insight on the optimization of the geometrical parameters which improve the thermal performances of a PEMFC, from a cooling strategy aspect point of view.
[Show abstract][Hide abstract] ABSTRACT: Is this paper, the electrodeposition/electrodissolution cycling of lead dioxide (PbO2) is studied on vitreous carbon electrodes in lead methanesulfonate/methanesulfonic acid medium for a soluble lead acid flow battery application. The influence of the active species concentrations (Pb2+, H+) on the cyclability of lead dioxide (charge efficiency, lifetime of cycling, etc.) is assessed. The proton has a very adverse effect when its concentration is above 1 M. Electrochemical impedance spectroscopy (EIS) shows that the lead dioxide layer can be passivated at the end of reduction when the electrolyte is strongly acidic. Mass changes investigations carried out during PbO2 cycling with a quartz crystal microbalance (QCM) confirm the presence of the solid-state reaction predicted in the literature. This side reaction suggests the formation of a non-stoichiometric PbOx compound with a poor solubility and a high electric resistance. The effect of the acid concentration as well as the current density on the formation of PbOx is assessed. The poor cyclability of PbO2 in high acidic media can be related to the accumulation of this resistive compound within the layer. Finally, considerations for an optimal operation of the battery are presented.
[Show abstract][Hide abstract] ABSTRACT: Mathematical modeling is an essential tool in the design of fuel cell systems, as it is important to understand the response of a stack under different conditions. This paper proposes a three dimensional electrical model of PEMFC stack. Such approach highlights the phenomena that occur at the macroscopic scale which are the electrical interactions taking place within the stack. At this scale, the microscopic phenomena are taken into account by averaging them over all the thickness of the membrane electrode assembly (MEA). This model consists of solving the charge transport equation in three dimensions. In order to avoid interfacial issues with the potential jump that occurs in the MEAs, a special source term is added in the transport equation. It makes the model robust, reliable, and helpful for under-standing the effect of anomalies on the electric behavior of a PEMFC stack. After describing the equations and the numerical method used for the model, the paper shows some electrical phenomena such as cells interactions, non-equipotential bipolar plate, higher cell voltages and internal loop of current.
[Show abstract][Hide abstract] ABSTRACT: This paper evaluates electrochemical noise (EN) technique as a possible tool for the diagnosis of Proton Exchange Membrane Fuel Cells (PEMFC) during operation. EN was employed to survey PEM single cell under various operating conditions at different humidification levels so as to focus on flooding or drying tendencies. Data was investigated in the frequency domain by means of power spectrum densities that showed to be sensitive to changes in the PEMFC operating conditions. EN seems an interesting way for an innovative and non-invasive on-line diagnosis tool.
[Show abstract][Hide abstract] ABSTRACT: This article presents experiments conducted with two single rectangular mini-channels of same hydraulic diameter (1.4 mm) and different aspect ratios for conditions of horizontal boiling flow. The Forane® 365 HX used was subcooled (ΔTsub = 15 °C) for all the boiling curves presented in the paper. Local heat transfer coefficients were measured for heat flux ranging from 25 to 62 kW m−2 and mass flux from 200 kg m−2 s−1 to 400 kg m−2 s−1. The boiling flows were observed with two different cameras (depending on the flow velocity) through a visualization window. The flow patterns in the two channels were compared for similar conditions. The results show that the boiling heat transfer coefficient and the pressure drop values are different for the two single mini-channels. For low heat flux condition, the channel with lowest aspect ratio (H/W = 0.143) has a higher heat transfer coefficient. On the other hand, for high heat flux condition, the opposite situation occurs, namely the heat transfer coefficient becomes higher for the channel with highest aspect ratio (H/W = 0.43). This is probably due to the earlier onset of dryout in the channel with lowest aspect ratio. For the two cases of heating, the pressure drop for the two-phase flow remains lower for the channel with lowest aspect ratio. These results show that the aspect ratio plays a substantial role for boiling flows in rectangular channels. As for single-phase flows, the heat transfer characteristics are significantly influenced (even though the hydraulic diameter remains the same) by this parameter.
[Show abstract][Hide abstract] ABSTRACT: The modeling of Li-ion batteries may work as a powerful tool for the introduction and widespread testing of this technology
in alternative energy storage, hybrid, and electric vehicle applications. In this paper, the authors propose a model for Li-ion
batteries that is based on a typical equivalent electrical circuit (EEC) representation of these batteries and valid over
a wide frequency range
. However, a full parameterization of EEC models was not possible only with the electrochemical impedance spectroscopy (EIS)
method, particularly at high charge/discharge currents. Therefore, a method combining EIS and charge/discharge curves analysis
has been developed. The simulated and experimental results were compared, and it was demonstrated that the developed method
provides accurate predictions of the dynamic behavior of Li-ion batteries over wide state of charge and charge/discharge current
Journal of The Electrochemical Society. 02/2011; 158(3):A326-A336.
[Show abstract][Hide abstract] ABSTRACT: Satisfactory power densities for Single Chamber Solid Oxide Fuel Cells (SC-SOFC) can be obtained with ceramic materials already used in dual chambers SOFC. In order to increase the oxygen access trough the cathode, the authors propose to combine a SC-SOFC and a dual chamber SOFC by using a porous ceramic membrane. In this computing work, species transport is governed by convection-diffusion equations in the gas channel and the porous media. In addition, momentum balances are solved using Brinkman formulation through the porous cell. Charge transfer occurs at the electrode/electrolyte interface and is described by the general Butler-Volmer equation. Simulations allow the calculation of the distributions of partial pressures for all the gas species within the cell (CH4, H2, CO, CO2, H2O, O2, N2). As expected, the injection of only 3% of the steam water increases the chemical conversion of methane.
[Show abstract][Hide abstract] ABSTRACT: This paper deals with one of the needs for PEMFC to be economically reliable: diagnosis tool for water management. This issue is actually a key parameter for both performance and durability improvement. Acoustic emission (AE) technique was employed to survey PEM single cell under various operating conditions. AE events coming from different sources have thus been identified, classified and finally ascribed to different phenomena induced by MEA water uptake and/or biphasic flow in the gas channel thanks to a statistical post-treatment of the acoustic data. Results, although qualitative, seems trusty enough to unravel hidden correlations between AE hits and physicochemical phenomena taking place during the cell operation and open up the way for an innovative and non-invasive online diagnosis tool.
Journal of Power Sources 12/2010; 195(24):8124-8133. · 5.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In recent years, fuel cell technology has attracted considerable attention from several fields of scientific research as fuel
cells produce electric energy with high efficiency, emit little noise, and are non-polluting. Solid oxide fuel cells (SOFCs)
are particularly important for stationary applications due to their high operating temperature (1,073–1,273K). Methane appears
to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by direct internal reforming
(DIR) within the SOFC anode. Unfortunately, internal steam reforming in SOFC leads to inhomogeneous temperature distributions
which can result in mechanical failure of the cermet anode. Moreover this concept requires a large amount of steam in the
fed gas. To avoid these problems, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam
reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However,
with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell
configuration of SOFC electrolyte support was studied. This configuration combined a catalyst layer (0.1%Ir–CeO2) with a classical anode, allowing GIR without coking. In order to optimise the process a SOFC model has been developed, using
the CFD-Ace+ software package, and including a thin electrolyte. The impact of a thin electrolyte on previous conclusions
has been assessed. As predicted, electrochemical performances are higher and carbon formation is always avoided. However a
sharp decrease in the electrochemical performances appears at high current densities due to steam clogging.
KeywordsSOFC-Gradual internal reforming-Simulation-CFD-Ace+
Journal of Applied Electrochemistry 01/2010; 40(5):943-954. · 2.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The diagnosis of flooding or drying is an important factor in improving the reliability and durability of PEMFCs. Indeed,
flooding and drying lead to a reduction in the output voltage delivered by the fuel cell. Among the various diagnostic techniques,
electrochemical impedance spectroscopy (EIS) is a powerful tool. In this study, EIS measurements were carried out on a 500W
stack comprised of 16 elementary cells. Electrochemical impedance spectra were recorded either on each cell or on the stack.
Use of an electrical equivalent circuit model revealed that flooding mainly affects the transfer resistance and the cathodic
Warburg impedance. A diagnostic tool based on these two components is proposed.
Journal of Applied Electrochemistry 01/2010; 40(5):911-920. · 2.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A model of a singular cell of an anode support SOEC is proposed in this work. The results of simulations will allow us to understand and to analyze the ionic and electronic ohmic drops effects on the cell performances. This paper proposes a model solution using the CFD-Ace+ software package to simulate the behaviour of this tubular SOEC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemistry in porous electrodes is described using Butler-Volmer equations at the triple phase boundary. The layout in 3D of the current densities, the electronic and ionic potentials allow the analysis of the respective ohmic drops. The simulation results emphasize the critical behaviour of SOEC such as the endothermic, exothermic and thermo-neutral operating mode.