Homework-2-solutions

Homework-2-solutions - 1 MEM 415 Fuel Cell Engines HOMEWORK...

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1 Dr. E. C. Kumbur | MEM-415 Fuel Cell Engines MEM 415 Fuel Cell Engines HOMEWORK SET#2 --- SOLUTIONS 1) (10%) Consider the following typical reactions for PEM fuel cells: a) (3%) Which reaction occurs at the anode of the fuel cell, and which reaction occurs at the cathode? b) (4%) Is this a galvanic or electrolytic cell? Explain why? c) (3%) Which is the positive electrode? Explain why? Solutions: a) The H 2 -- 2H + + 2e - hydrogen oxidation reaction occurs at the anode, whereas the 4H + +4e - +O 2 --- 2H 2 O oxygen reduction reaction occurs at the cathode. b) A fuel cell is power producing, or galvanic. c) The positive electrode in a galvanic cell such as a fuel cell is the cathode. 2) (15%) Consider a 15 cell hydrogen/air PEM fuel cell stack producing a total of 1.0 kW at 10 V? a) (5%) What is the mass flow rate of hydrogen if the anode stoichiometry is 1.3? b) (5%) What is the rate of generation of water at the cathode, in grams per hour? c) (5%) If the theoretical maximum voltage of a single cell is 1.23 V, what is the voltaic efficiency of a single cell, assume all cells have the same voltage? Solutions: a) P= 1.0 kW @ V= 10V, so current will be: I= P/V = 1000/10= 100 Amps @ Anode: H 2 -- 2H + + 2e - @ Cathode: 2H + +2e - +0.5O 2 ---H 2 O In terms of grams: Now, you need to multiply by 15 (since the cells are in series) to find out the total mass flow rate of hydrogen in the system:
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Homework-2-solutions - 1 MEM 415 Fuel Cell Engines HOMEWORK...

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