The catalytic theory

Tafel proposed that (5)(i) of the above scheme was the slow stage. Since the standard potential of a hydrogen electrode is zero, by definition, its potential, under conditions other than standard may be given by 

Equation (8.52) is of the form of the Tafel equation (8.33) which suggests that b is approximately 0-03. Such a value is rarely encountered in practice although it is observed in the case of platinized platinum. The above treatment does not allow for the fact that the pH of the solution will be modified by the adsorption process, relative concentrations of free and adsorbed atoms being given by the Freundlich isotherm 

Inclusion of this restriction requires modification of Equation (8.52) to the following 

---