E10-MSE-B_PS4_solns - E10 Problem Set #4 Solutions...

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E10 – Problem Set #4 Solutions Materials Science and Engineering Module on Batteries and Fuel Cells Was due: 5:10PM on Wednesday, November 17, 2010 1 of 4 Current vs. voltage plot of a complete zinc-air battery. Facts: (1) V eq Zn is approximately 0.7V lower that V eq H , which is approximately 1.2V lower than V eq O . (2) The ratio of exchange current densities for Zn:H:O are 10 -3 : 1 : 10 -6 . (3) The rate of each reaction changes by a factor of 10 for each 100 mV change in potential. (4) The current, I, is positive for oxidation reaction rates and is negative for reduction reaction rates. 1. The plot of Log I net Zn.total vs V for zinc immersed in air-saturated aqueous electrolyte that you constructed in the previous problem set is reproduced above. On the same plot, show Log I net Pt vs V for platinum immersed in the same solution. The exchange current density of the O/OH - redox system on platinum is about 10 6 times greater than that on zinc. Recall we have defined the net current as: I net XX = I ox XX + I red XX . On the figure label the potential difference between an electrode of zinc and an electrode of platinum immersed in the aqueous electrolyte. Next, identify the potentials of zinc and platinum when the two electrodes are shorted (i.e., connected by a zero resistance wire). Indicate the direction of electron flow through the wire connecting the zinc and platinum electrodes. Identify the value
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E10-MSE-B_PS4_solns - E10 Problem Set #4 Solutions...

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