Abstract
The dependence of the rate of the oxygen reduction on the nature of cations [Li+, Na+, K+, Rb+, Cs+, (CH3)4N+] is studied at smooth platinum and porous carbon loaded with a platinum catalyst in alkaline solutions.
The rest potentials are shifted to more negative values from Li+ to (CH3)4N+, likewise the cathodic polarization is increased with the size of the cations. A change of the potential drop within the diffuse double layer caused by increasing cation concentration with growing size of ions is of minor importance in 0.5N alkaline solutions. Specific adsorption of (Rb+), Cs+ and (CH3)4N+ has to be considered, which would give rise to a decrease of the rate of the electrochemical reaction.
Secondly the observed effect can be attributed to ion pairing of charged species (O2 −) involved in the overall reaction and the cations. The stability of the hyperoxide ion is increased from (CH3)4N+ to Li+ by interaction with the cations. Consequently the velocity of the rate determining charge transfer step is accelerated in this direction.
The experimental findings are in favour of the second interpretation, because the effect is not enhanced in more dilute solutions.
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Fabjan, C., Lopreis, A. & Neckel, A. Der Einfluß der Kationen alkalischer Elektrolyte auf die Geschwindigkeit der kathodischen Sauerstoffreduktion an Platin. Monatshefte für Chemie 107, 1209–1219 (1976). https://doi.org/10.1007/BF00903809
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DOI: https://doi.org/10.1007/BF00903809