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Title: Oxygen electrode reaction in molten carbonate fuel cells

Abstract

Molten carbonate fuel cell system is a leading candidate for the utility power generation because of its high efficiency for fuel to AC power conversion, capability for an internal reforming, and a very low environmental impact. However, the performance of the molten carbonate fuel cell is limited by the oxygen reduction reaction and the cell life time is limited by the stability of the cathode material. An elucidation of oxygen reduction reaction in molten alkali carbonate is essential because overpotential losses in the molten carbonate fuel cell are considerably greater at the oxygen cathode than at the fuel anode. Oxygen reduction on a fully-immersed gold electrode in a lithium carbonate melt was investigated by electrochemical impedance spectroscopy and cyclic voltammetry to determine electrode kinetic and mass transfer parameters. The dependences of electrode kinetic and mass transfer parameters on gas composition and temperature were examined to determine the reaction orders and the activation energies. The results showed that oxygen reduction in a pure lithium carbonate melt occurs via the peroxide mechanism. A mass transfer parameter, D{sub O}{sup 1/2}C{sub O}, estimated by the cyclic voltammetry concurred with that calculated by the EIS technique. The temperature dependence of the exchange current density andmore » the product D{sub O}{sup 1/2}C{sub O} were examined and the apparent activation energies were determined to be about 122 and 175 kJ/ mol, respectively.« less

Authors:
;
Publication Date:
Research Org.:
Texas A and M Univ., College Station, TX (United States). Dept. of Chemical Engineering
Sponsoring Org.:
USDOE; USDOE, Washington, DC (United States)
OSTI Identifier:
7295482
Report Number(s):
DOE/PC/79931-T13
ON: DE92040180
DOE Contract Number:
FG22-87PC79931
Resource Type:
Technical Report
Resource Relation:
Other Information: Thesis (Ph.D.). Contains thesis by Bhasker B. Dave: Oxygen reduction in lithium carbonate melt: Determination of electrode kinetic and mass transfer parameters
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; ELECTRODES; CHEMICAL REACTIONS; MOLTEN CARBONATE FUEL CELLS; ACTIVATION ENERGY; ENERGY EFFICIENCY; LITHIUM CARBONATES; MASS TRANSFER; OXYGEN; PROGRESS REPORT; REDUCTION; VOLTAMETRY; ALKALI METAL COMPOUNDS; CARBON COMPOUNDS; CARBONATES; DIRECT ENERGY CONVERTERS; DOCUMENT TYPES; EFFICIENCY; ELECTROCHEMICAL CELLS; ELEMENTS; ENERGY; FUEL CELLS; HIGH-TEMPERATURE FUEL CELLS; LITHIUM COMPOUNDS; NONMETALS; OXYGEN COMPOUNDS; 300502* - Fuel Cells- Performance & Testing

Citation Formats

Appleby, A.J., and White, R.E.. Oxygen electrode reaction in molten carbonate fuel cells. United States: N. p., 1992. Web. doi:10.2172/7295482.
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Appleby, A.J., & White, R.E.. Oxygen electrode reaction in molten carbonate fuel cells. United States. doi:10.2172/7295482.
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Appleby, A.J., and White, R.E.. Tue . "Oxygen electrode reaction in molten carbonate fuel cells". United States. doi:10.2172/7295482. https://www.osti.gov/servlets/purl/7295482.
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@article{osti_7295482,
title = {Oxygen electrode reaction in molten carbonate fuel cells},
author = {Appleby, A.J. and White, R.E.},
abstractNote = {Molten carbonate fuel cell system is a leading candidate for the utility power generation because of its high efficiency for fuel to AC power conversion, capability for an internal reforming, and a very low environmental impact. However, the performance of the molten carbonate fuel cell is limited by the oxygen reduction reaction and the cell life time is limited by the stability of the cathode material. An elucidation of oxygen reduction reaction in molten alkali carbonate is essential because overpotential losses in the molten carbonate fuel cell are considerably greater at the oxygen cathode than at the fuel anode. Oxygen reduction on a fully-immersed gold electrode in a lithium carbonate melt was investigated by electrochemical impedance spectroscopy and cyclic voltammetry to determine electrode kinetic and mass transfer parameters. The dependences of electrode kinetic and mass transfer parameters on gas composition and temperature were examined to determine the reaction orders and the activation energies. The results showed that oxygen reduction in a pure lithium carbonate melt occurs via the peroxide mechanism. A mass transfer parameter, D{sub O}{sup 1/2}C{sub O}, estimated by the cyclic voltammetry concurred with that calculated by the EIS technique. The temperature dependence of the exchange current density and the product D{sub O}{sup 1/2}C{sub O} were examined and the apparent activation energies were determined to be about 122 and 175 kJ/ mol, respectively.},
doi = {10.2172/7295482},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jul 07 00:00:00 EDT 1992},
month = {Tue Jul 07 00:00:00 EDT 1992}
}
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Technical Report:
View Technical Report (10.14 MB)
DOI:  10.2172/7295482
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  • ; ; ; ...
    The high temperature apparatus for investigations of electrode kinetics of oxygen reduction on test electrodes in molten carbonates was tested using Li/sub 2/CO/sub 3/ melt and a gold flag test electrode. Potential sweep data for oxygen reduction reaction at the gold electrode in Li/sub 2/CO/sub 3/ melt were obtained and the results were found to be in agreement with the available data in literature. AC impedance measurements, as a function of frequency, are in progress to evaluate the kinetic parameters for peroxide reduction in Li/sub 2/CO/sub 3/melt. A complex nonlinear least square parameter estimation program, based on equivalent circuit model,more » is employed to analyze the ac impedance data. One of the designs being considered for the microelectrode (to be used to determine the transport parameters of the intermediate species (O/sub 2/- and O/sub 2//sup 2/-) and the electrode kinetic parameters for oxygen reduction in molten carbonates) is a fine wire (diameter of 25 ..mu..m or less) anchored on an alumina tube with a ceramic adhesive. This design is being initially tested for oxygen reduction in an aqueous medium. For this purpose, a cylindrical microelectrode of gold is being used in aqueous KOH solution for the simultaneous determination of diffusion coefficient and solubility of oxygen from the transient measurements of the potential step experiments. Several ceramic adhesives are being evaluated for their stability in molten carbonate environment. The stable ceramic adhesive will be utilized for leak-proof sealing of the test electrode (fine wire) to the open end of the alumina tube. 9 figs.« less

  • ; ;
    The oxygen cathode of the molten carbonate fuel cell is still not well understood because of the uncertain nature of the reaction mechanism. The objectives of this project include a study to examine the kinetics of oxygen reduction in molten carbonate fuel cells by unambiguous methods that allow the determination of the rate determining steps and the reaction parameters. The data from such kinetic studies require sophisticated analytical techniques for obtaining the kinetic mechanism that best fits the data and, consequently, the best estimates of the reaction parameters. 1. A program has been written to simulate the reaction sequences formore » oxygen reduction in a molten carbonate fuel cell at a rotating disk electrode. 2. The reaction sequence for the superoxide mechanism was simulated using assumed and literature values for the reaction parameters.« less

  • ; ; ; ...
    The high temperature equipment necessary for the investigation of oxygen reduction kinetics using microelectrodes was set up. Three types of microelectrodes were designed and fabricated. Experiments are underway to examine the microelectrodes in respect to (1) their stability in the molten carbonate environment; (2) oxygen reduction kinetics and mass transport parameters in aqueous electrolytes for comparison with similar results using other techniques; and (3) oxygen reduction kinetics and mass transport parameters in molten carbonate electrolytes. The reaction sequences for oxygen reduction in melts of various carbonate mixtures were simulated on the basis of a postulated kinetic model involving the reductionmore » of O/sub 2//sup 2/minus// and O/sub 2/minus// ions at the electrode. Auto-catalytic reactions involving the reaction of O/sub 2//sup 2/minus// and O/sub 2/minus// species with O/sub 2/ and the neutralization reaction of O /sup 2/minus// ions by CO/sub 2/ in the melt were taken into account. Enhancement of oxygen reduction currents occurs at high rates of oxygen dissolution in the melt. Changes in the auto-catalytic reaction rates of O/sub 2//sup 2/minus// and O/sub 2/minus// affect the polarization curves significantly only in the presence of dissolved oxygen in the melt. 8 figs.« less

  • ; ; ; ...
    The oxygen reduction reaction on a gold electrode in lithium carbonate melt was investigated to determine the influence of partial pressure of carbon dioxide and and temperature on electrode kinetic and oxygen solubility by using cyclic voltammetry and impedance analysis techniques. During this quarter, the impedance data were analyzed by a Complex Nonlinear Least Square (CNLS) parameter estimation program to determine the kinetic and the mass transfer related parameters such as charge transfer resistance, double layer capacitance solution resistance, and Warburg coefficient. The estimated parameters were used to obtain the CO{sub 2} reaction orders and apparent activation energies for themore » exchange current density and the mass transfer parameter (D{sub O}{sup 1/2}C{sub O}*). 7 refs., 11 figs., 4 tabs.« less

  • ; ; ; ...
    The following preliminary conclusions can be drawn from the results so far: 1) The effect of the neutralization reaction rate on the steady state polarization curves is the same for both models. 2) Changes in the auto-catalytic decomposition rates of O/sub 2//sup /double bond// and O/sub 2//sup /-// do not affect the polarization curves significantly. 3) The fact that the contribution to the overall steady polarization curve can be attributed predominantly to the reduction of O/sub 2//sup /double bond// contradicts the results of Vogel et al. in which the steady state experimental polarization curves were attributed mainly to the reductionmore » of O/sub 2//sup /-// species. Therefore, the results of Vogel et al. are at best in closer agreement with Model A than with Model B.« less