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ENGRI_111_hw4_2007 - When the two half reactions at the...

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ENGRI 111 Homework #4 Due Monday, October 22 1. Solar cell A uses a semiconductor with a band gap of 1 eV. Solar cell B uses a semiconductor with a band gap of 2 eV. Either cell is thick enough to absorb all the light above its band gap. Both cells can work simultaneously with one on the top of the other to operate more efficiently in a small space. a) Which cell has to be on top (first to receive the sunlight) for both to work simultaneously, and b) why? 2. In both the conventional solar cell based on p-n junctions and the Gratzel cell, charge carriers are produced by the absorption of light. However the mechanisms for bringing the charge carriers out to current carrying connections are different. Compare briefly how charge carriers move in these cells. 3) In a fuel cell two half reactions are involved. A half reaction is charge balanced (ie there is the same total charge on each side of the reaction) but involves production or consumption of electrons. Half reactions, however, are half of the story.
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Unformatted text preview: When the two half reactions at the cathode and anode of a cell (battery, fuel cell, etc.) are combined, the cell discharge reaction can be described. a) What is the half-reaction for electron production at the anode? b) What is the half-reaction for electron consumption at the cathode? c) What is the full cell discharge reaction?—remember, water should be one of the reaction products. 4) The lead-acid battery uses lead and lead oxide as the two electrodes. The electrolyte is sulfuric acid. a) What is the anode and what is the cathode? b) Write down the half-reaction for electron production at the anode including sulfate ions b) Write down the half reaction for electron consumption at the cathode including sulfate ions c) Combine these two half reactions to form the full discharge reaction for the battery. 5) What are the benefits for having a solid electrolyte in a battery? If they are attractive what has prevented their use to date?...
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