Oxygen reduction on silver catalysts in solutions containing various concentrations of sodium hydroxide - comparison with platinum

In air cathodes for chlorine-sodium hydroxide production, silver is a suitable catalyst for the oxygen reduction reaction (ORR), as is platinum. The ORR mechanism, studied with both rotating disc and ring-disc electrodes and impedance spectroscopy, is first order towards O-2. However, the reaction can involve a direct four-electron or two-electron pathway. Although the latter involves different chemistry, including decomposition of hydrogen peroxide, the two pathways are difficult to distinguish, probably because they have the same rate-determining step. Considering kinetics/solubility ratios, temperature increase favours the ORR kinetics on both metals, whereas an increase in sodium hydroxide concentration is only positive for silver: for high sodium hydroxide concentration, platinum properties are hindered by greater adsorbed oxygenated species coverage. Thus, silver becomes competitive to platinum in high concentration alkaline media.