Addendum The Tafel Slope and Reaction Mechanism in Electrocatalysis

Addendum The Tafel Slope and Reaction Mechanism in Electrocatalysis 

The Tafel slope can be used to determine the rate-determining steps in electrochemical systems We describe Tafel slope plots and illustrate their use here. We start by analyzing the mechanisms for hydrogen evolution reactions by plotting the exchange current density as a function of overpotential. Two different mechanisms, labeled here as A and B, can be considered  

When the electron-transfer step (1) is rate limiting, one cannot distinguish between the two mechanisms. The rate of reaction (1) can be written as 

One can then assume a Brpnsted-Evans-Polanyi relationship to relate the dependence of rate constant fc i to the overpotential E  

The value of a is typically assumed to be equal to 0.5. If step 2, in mechanism A is rate determining  

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