Effects of heteropolynanions (HPA) on the activities and stabilities of some cobalt macrocyclic compounds for O{sub}2 electroreduction in acid media

摘要

In literature reports several groups have stressed the role of HPA adsorption on some porphyrin supplied with four peripheral groups with nitrogen atoms in low oxidation states. The HPA effect in the ratio 4 HPA per 1 mole cobalt macrocycle was to enhance the 4 electron reduction process compared to the 2 electron pathway. All the experiments were carried out with deposited porphyrins on pyrolytic graphite. The aim of the present paper was to get some insight on the interest of HPA adsorption on cobalt macrocycles deposited by a sublimation mode on an active charcoal SX Ultra. Two macrocycles were selected CoP(py){sub}4 from previous studies and CoTAA for its performances under fuel cell conditions. (Co tetraazaannulene) The salient feature of this work concerns the beneficial effect found for HPA adsorption as far as the CoN{sub}4 moiety is conserved. Electrochemical experiments were conducted using the rotating disk technique (RDE) and the duration tests were operated under 100 h in acid solution, HPA adsorption would favour the longevity. This effect on the basis of previous investigations could be correlated to the enhancement of electronic density near the cobalt ion.