The Kinetics of Oxygen Reduction at Porous Teflon‐Bonded Fuel Cell Electrodes

Oxygen reduction on porous Teflon‐bonded semihydrophobic electrodes has been investigated using the impedance method. Carbon‐supported metals and activated carbon have been used as electrocatalysts in neutral and alkaline electrolytes. The results of the impedance measurements agree well with those of galvanostatic double‐pulse experiments. Taking into account the internal structure, especially the large inner surface area of the catalyst particles forming the electrode, an attempt is made to calculate exchange current densities from the apparent charge transfer resistance. The values of support the assumption that hydrogen peroxide is the predominant reduction product formed on the electrocatalysts investigated. The measured polarization resistance is mainly caused by the slow diffusion of oxygen and its reduction products. The rather fast adsorption of oxygen and charge transfer reaction cause only a small contribution to the polarization. The results are discussed with respect to the electrode structure and compared with a general model describing the operation of a semihydrophobic porous electrode.