I have calculated the exchange current density from the equation -Alogio = intercept of the tafel plot for two electrocatalysts. For catalyst A, a tafel slope of 124mV/dec yields me a ECD value of 0.358mA while catalyst B , with a tafel slope of 84mV/dec yileds a value of 0.003mA. From the tafel values, catalyst A is better, while from the exchange current density values, catalyst B is said to be better. This is a contradiction. Could someone please guide me as to where is my error?
Your error is in definitions. There is no a single criteria to compare the catalyst activity. Personally, I would use the turnover frequency (TOF) to characterize the "speed" of the catalyst. Turnover number (TON) is directly related to the catalyst stability. TON and TOF might depend on over-potential, the maximum TOF could be achieved at different conditions (e. g. pH). Thus, there is no contradiction. You can't say which catalyst is better.
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