An extensive treatment of the agglomerate model for porous electrodes in molten carbonate fuel cells—II. Quantitative analysis of time-dependent and steady-state model

Prins-Jansen, J.A.; Hemmes, K.; Wit, J.H.W. de

doi:10.1016/s0013-4686(97)00137-0

Cited by 10 publications

(4 citation statements)

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“…According to the superoxide reaction mechanism (PrinsJansen et al [22,23]), a negative order of reaction with respect to carbon dioxide is used for the cathodic reduction kinetics. Thus, the current density increases towards the end of the cathode channel, where the carbon dioxide fraction is low.…”

Section: Current Density Distributionmentioning

confidence: 99%

Stack Modelling of a Molten Carbonate Fuel Cell (MCFC)

2010

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A model of a molten carbonate fuel cell (MCFC) stack including internal steam reforming is presented. It comprises a symmetric section of the stack, consisting of one half indirect internal reforming unit (IIR) and four fuel cells. The model describes the gas phase compositions, the gas and solid temperatures and the current density distribution within the highly integrated system. The model assumptions, the differential equations and boundary conditions as well as the coupling equations used in the model are shown. The strategy to solve the system of partial differential equations is outlined. The simulation results show that the fuel cells within the stack operate at different temperatures. This is expected to have an impact on the voltages as well as the degradation rates within the individual fuel cells. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim [accessed September 2nd, 2010

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Section: Current Density Distributionmentioning

confidence: 99%

Stack Modelling of a Molten Carbonate Fuel Cell (MCFC)

2010

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“…Both points are consistent with much of the previous work discussed in the introduction. 1,4,6,7 In particular, given the physical parameters described above, for high inlet gas concentrations, the dominant polarization loss is the ohmic loss.…”

Section: Discussionmentioning

confidence: 99%

“…Their work does not distinguish the roles of gas-phase and electrolyte-phase transport. Prins et al [2][3][4] also made ac impedance measurements; they concluded that for relatively rich inlet gas concentrations, the polarization losses are dominated by ohmic loss ͑electrolyte conduction͒. For lower inlet gas concentrations, electrolyte diffusive transport became more significant.…”

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confidence: 99%

“…For lower inlet gas concentrations, electrolyte diffusive transport became more significant. 4 Fehribach et al 5 directly computed the current production in a small 100 ϫ 100 m cathode cross section, and found that on this scale, the diffusive transport in the electrolyte is the greatest contributor to the polarization loss. Kunz and Murphy, 6 on the other hand, suggest that gas-phase diffusional resistance increases with decreasing inlet gas concentrations and accounts for a significant portion of the polarization loss.…”

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Estimates for Polarization Losses in Molten Carbonate Fuel Cell Cathodes

Fehribach

Hemmes

2001

J. Electrochem. Soc.

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This paper compares the polarization losses associated with the various diffusion-reaction-conduction processes in molten carbonate cathodes. The comparisons are made by estimating each type of loss in terms of component electrochemical potentials in joules/mole; this allows diffusive, charge-transfer, and ohmic losses to all be put on equal footing. For characteristic parameter values, diffusion in both the gas and electrolyte phases and conduction in the electrolyte account for similar polarization losses; charge-transfer and conduction in the solid electrode account for significantly smaller losses. These results tend to support and unify the previous work of numerous investigators. Also molecular-channel interactions are found not to contribute significantly to the polarization loss.In recent years, a number of studies have attempted to determine which portion of the overall cathodic process accounts for the majority of polarization losses in molten carbonate fuel cell ͑MCFC͒ cathodes. These studies have resulted in a variety of conclusions, some of which may at first glance appear contradictory. Through ac impedance measurements, Yuh and Selman 1 found that chargetransfer accounts for the majority of the overall polarization loss at lower temperatures ͑600°C͒, while mass transport ͑diffusion͒ and/or slow recombination are more important at higher temperatures ͑700°C͒. Their work does not distinguish the roles of gas-phase and electrolyte-phase transport. Prins et al. 2-4 also made ac impedance measurements; they concluded that for relatively rich inlet gas concentrations, the polarization losses are dominated by ohmic loss ͑electrolyte conduction͒. For lower inlet gas concentrations, electrolyte diffusive transport became more significant. 4 Fehribach et al. 5 directly computed the current production in a small 100 ϫ 100 m cathode cross section, and found that on this scale, the diffusive transport in the electrolyte is the greatest contributor to the polarization loss. Kunz and Murphy, 6 on the other hand, suggest that gas-phase diffusional resistance increases with decreasing inlet gas concentrations and accounts for a significant portion of the polarization loss. Recent work by Peelen et al. 7 found that in particular a carbon dioxide partial pressure below 0.05 atm was detrimental to a MCFC cathode current density of 150 mA/cm 2 .The present work is a brief, but we hope useful, theoretical estimate of the polarization losses in MCFC cathodes; it supports and reinforces many of the conclusions discussed above, and to some extent, unifies them. The estimates are made using the component electrochemical potentials introduced by Fehribach et al. 5,8,9 This formulation is particularly useful here because it allows the various cathodic processes ͑diffusion, conduction, electrochemical reactions͒ to be compared on the same scale ͑i.e., equal footing͒. This work differs from our earlier work 5 in that here we are considering an entire laboratory cathode ͑800 m thick͒ rather than a small cross section, and that ...

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