C. Kang et al., CATALYTIC PATHWAYS FOR THE ELECTROREDUCTION OF O-2 AT GRAPHITE-ELECTRODES ON WHICH A MACROCYCLIC COBALT COMPLEX IS ADSORBED, Journal of electroanalytical chemistry [1992], 413(1-2), 1996, pp. 165-174
The electroreduction of O-2 at graphite electrodes on which the comple
x of Co(III) with the macrocyclic ligand 14,14-hexamethyl-1,4,8,11-tet
raazacyclotetradecane (hmc) is adsorbed proceeds in two steps that are
well separated in potential. The first step consumes two electrons pe
r molecule of adsorbed (hmcCo3+ to yield adsorbed (hmc)CoOOH2+. The se
cond step involves the reduction of the adsorbed (hmc)CoOOH2+ to (hmcC
o2+ + H2O2 followed by the reduction of O-2 to H2O2 catalyzed by the a
dsorbed (hmc)Co-3+/2+ complexes. A mechanistic scheme that accommodate
s the observed electrochemical responses is presented and tested by co
mparison with responses calculated by digital simulation methods. Diff
erences between the electrochemical responses obtained with dissolved
or adsorbed (hmcCo3+ are exposed and discussed. In addition, the behav
ior of the adsorbed (hmc)Co-3+/2+ system as it acts to electrocatalyze
the reduction of O-2 is compared and contrasted with that exhibited b
y analogous adsorbed cobalt porphyrin electrocatalysts.