Kinetic Parameters of the Hydrogen Oxidation Reaction

The Tafel equation rj = / xexp(z/Zo) describes the relationship between overpotential and current density. Two parameters, i.e., exchange current density z and Tafel slope b, are the most important kinetic parameters to measure the electrochemical activity of an electrode material. Exchange current density z is analogous to the rate constant used in chemical kinetics, and a high value of i often translates into a fast electrochemical reaction. On the other hand, a smaller Tafel slope is desirable from the kinetic point of view to obtain a smaller overpotential. As for any electrochemical reaction, the Tafel slope h is a function of temperature in the form RT 

It must be noted that those kinetic parameters depend not only on the measurement conditions, such as temperature, but also on the structures of flie catalyst. Table 3.2 lists the exchange current density of the HOR as a function of temperature on the PtRu/C anode in a real PEM fuel cell, measured and simulated by Song et al. [8] and Zhang et al. [47]. 

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