Oxygen reduction reaction kinetic current

Currently used electrode-catalysts (anode and cathode) consist of an assembly of metallic nanoparticles usually deposited on an electronic conducting substrate and embedded in a hydrated membrane [10, 11], which is the polymer electrolyte proton-conductive material (Figure 17.1). What differs between cathode and anode is the catalyst material, and also the significantly slow kinetics of the cathode oxygen reduction reaction compared to that of the anode hydrogen oxidation reaction. For this reason, several... 

The standard reduction potential of this reaction is around 0.21 V, much lower than the standard reduction potential of oxygen (R. 2.6) therefore, a mixed potential between 0.21 and 1.18 V is produced. Since the oxygen reduction reaction and Pt oxidation reaction dominate at the cathode due to kinetic reasons, the mixed potential is near the higher end. The other reason is hydrogen crossover through the PEM from the anode to the cathode. This is like an internal current flow in the cell and thus leads the electrodes (mainly the cathode) away from the 0 current thermodynamic equilibrium conditions. Due to the slow kinetics of Reaction 2.6, this internal current flow significantly lowers the cathode potential. Detailed estimation is given later in this chapter. For these two reasons, the OCV of a PEMFC is typically between 0.95 and 1.0 V. 

The kinetic current of the oxygen reduction reaction normalized by the mass of Pt metal cmitained in the electrocatalyst. 

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