MIT10_626S11_assn03

MIT10_626S11_assn03 - 10.626 Electrochemical Energy Systems...

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10.626 Electrochemical Energy Systems Spring 2011 MIT, M. Z. Bazant Problem Set 3 Faradaic Reaction Kinetics Due: Lecture 17 1. Direct methanol fuel cell (DMFC) reaction kinetics. The anode is fed with a methanol- water fuel and produces carbon dioxide, which escapes into the solution. The reaction pro- duces protons, which cross a polymer electrolyte membrane (PEM) to the cathode, where reduction occurs with oxygen gas (from air exposure) to produce water. The half-cell reac- tions are anode: CH OH + H O 6 H + 3 2 + 6 e + CO 2 3 cathode: O + 2 2 + 6 H + 6 e 3 H 2 O 3 net reaction (combustion): CH 3 OH + O 2 2 H 2 2 O + CO 2 Suppose that the limiting current is set by slow reaction kinetics at the anode and that the reaction occurs in two steps: fast adsorption onto the surface of the catalyst, and slow oxidation of the hydrogen. (a) Model methanol in solution as a hard-sphere liquid with volume fraction Φ = c M V M , using the Carnahan-Starling equation of state, where c M is the methanol concentration and V M the excluded volume. Model adsorbed methanol on the catalyst as a
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This note was uploaded on 11/27/2011 for the course CHEMICAL E 20.410j taught by Professor Rogerd.kamm during the Spring '03 term at MIT.

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MIT10_626S11_assn03 - 10.626 Electrochemical Energy Systems...

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