If = 12 , an electrode interface is unable to rectify alternating current because the

Chapter 25, Problem 25.28

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If = 12 , an electrode interface is unable to rectify alternating current because the current density curve is symmetrical about = 0. When 12 , the magnitude of the current density depends on the sign of the overpotential, and so some degree of faradaic rectification may be obtained. Suppose that the overpotential varies as =0 cost. Derive an expression for the mean flow of current (averaged over a cycle) for general , and confirm that the mean current is zero when = 12 . In each case work in the limit of small 0 but to second order in 0F/RT. Calculate the mean direct current at 25C for a 1.0 cm2 hydrogenplatinum electrode with = 0.38 when the overpotential varies between 10 mV at 50 Hz.