The effects of cyanide on the electrochemical properties of transition metal macrocycles for oxygen reduction in alkaline solutions

In order to obtain further insight into the redox properties and the oxygen reduction electrocatalysis on macrocycles, the effect of cyanide, capable of coordinating with the transition metal in the axial position, has been examined. These studies have been conducted with Fe- and Co-tetrasulfonated phthalocyanines adsorbed at the monolayer level on an ordinary pyrolytic graphite (OPG) rotating disk electrode. Fe and Co tetramethoxyphenyl porphyrins adsorbed on Vulcan XC-72 carbon at monolayer coverages have also been examined in 0.1 M NaOH in the form of a thin porous coating on an OPG disk with Teflon as the binder. The major focus has been on the blocking of the axial positions of the transition metal with CN− and the resulting effects on the redox couples as well as on O2 reduction. The data indicate that a strong axial interaction of O2 with the transition metal in the macrocycle is an important factor for O2 electrocatalysis. These blocking effects confirm the assignment of the peaks in cyclic voltammetry curves and the importance of particular redox couples to the O2 electrocatalysis.