Electrode cleaning and anion effects on ks for K3Fe(CN)6 couple

The effects of 17 different platinum electrode cleaning procedures on the heterogeneous rate of electron transfer (k_s) for the potassium ferri/ferrocyanide couple in 1 M aqueous KCl were investigated. The method yielding the most reproducible/high k_s (0.21 ± 0.04 cm s^?1) values was that of aque regia, pulse (cathodic, anodic, cathodic), and flame. Utilizing this cleaning procedure and the same couple, both cation and anion effects on k_s were examined. The previously noted cation effect on k_s was confirmed with Cs > K > Na > Li. Some discrepancy however, was noted for the tetra-alkylammonium salts. The anion effect was found to be larger than that of cations. Closer examination revealed the effect to be primarily due to adsorption of the halide. This adsorption effect further confirms the cleaning method choice since the method will allow the most halide to be adsorbed thus yielding the highest k_s.