Oxygen reduction in lithium carbonate melt : determination of electrode kinetic and mass transfer parameters /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
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| Subjects: | |
| Online Access: | ProQuest, Abstract Link to OAKTrust copy |
| 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. The oxygen reduction reaction in molten alkali carbonate electrolyte is complex and does not directly involve molecular oxygen. The oxygen reduction mechanism strongly depends on the cations present in the melt. Oxygen reduction on a fully-immersed gold electrode in a lithium carbonate melt was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) to determine electrode kinetic and mass transfer parameters. The impedance spectra were analyzed using the Randles-Ershler equivalent circuit model and Complex Nonlinear Least Square (CNLS) program to determine parameters such as the charge transfer resistance, Warburg coefficient, double layer capacity, and uncompensated electrolyte resistance. Cyclic voltammetric measurements showed that oxygen reduction in a pure lithium carbonate melt is very rapid. The invariance of peak potential with respect to the scan rate and linear behavior of the peak current density with respect to square root of the scan rate indicated that the oxygen reduction in a pure lithium carbonate melt is "reversible" up to 200 mV/s. 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[o]^(1/2)C[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[o]^(1/2)C[o] were examined and the apparent activation energies were determined to be about 122 and 175 kJ/mol, respectively. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Chemical Engineering." |
| Physical Description: | xiv, 152 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |