On the reduction of oxygen from dispersed media

The reduction of oxygen from an organic phase dispersed in a concentrated electrolyte is investigated. Dispersed organic phases are used to enhance oxygen transport in fermenters and artificial blood substitutes. This work evaluates the feasibility of using a dispersed organic phase to transport oxygen in a fuel cell. An emulsion of perfluorohexane in a 20 wt% potassium hydroxide solution was formed with a lecithin surfactant. Oxygen was reduced from the emulsion on a rotating disk electrode. The dispersed phase did not contribute to the oxygen transport to the surface of a rotating disk electrode. An explanation is given based on the hydrodynamics of an emulsion under a rotating disk electrode. To eliminate the effect of hydrodynamics, the results of a hydrostatic transient diffusion experiment (Cottrell Experiment) are reported. Again, no significant enhancement of the oxygen transport rate was observed. The dispersed phase is shown to contain oxygen by NMR spectroscopy. It is argued that the expectation of an enhancement from the use of a dispersed phase may be based on inapplicable transport models. The presence of the lecithin surfactant may also impede transport. An oscillating electrode is used to reduce oxygen from a continuous perfluorohexane phase. In this case, the rate of reduction of oxygen is limited by diffusion across an aqueous layer trapped at the surface of the electrode by its relative affinity for aqueous solution over perfluorohexane. The implications for the use of a dispersed organic phase in fuel cells are discussed. The use of a rotating disk electrode in heterogeneous media and the need for a mass transport model in liquid-liquid dispersions are also discussed.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Roushdy, Omar H., 1977-

Advisor dc:contributor.advisor

• Donald R. Sadoway and Ain A. Sonin.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/46493

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/46493