| Surface cyclic voltammetry was employed to study the electrochemistry of cationic porphyrazines: CoTmtppa, CoPz, and H2Pz. Due to their electron-withdrawing methylpyridinium substituents, these species were easier to reduce than normal phthalocyanines. Successive two-electron redox processes were observed. The number of electrons involved in each wave was calculated or deduced, and the number of protons simultaneously coupled was determined by pH dependence study. We then derived ion pairs by combining cationic porphyrin/porphyrazine (H2TAPP, CoTmtppa, CoPz, or H2Pz) and anionic phthalocyanine (CoTCPc). While the H2TAPP-CoTCPc ion pair could be characterized by UV spectra and surface cyclic voltammetry, those ion pairs made from the cationic porphyrazines and CoTCPc could only be constructed on a graphite electrode surface in bilayer conformations and studied by surface electrochemical techniques, because of solubility and stability limitations. The surface cyclic voltammogram of each ion pair consistently indicated evident coupling between the π-systems of the moieties. We further studied the electrocatalytic activity of the cationic porphyrazines and their ion pairs with CoTCPc, toward oxygen and hydrogen peroxide reduction and oxalate ion oxidation. Like most cobalt phthalocyanines and porphyrins, CoTmtppa and CoPz only catalyzed the two-electron reduction of oxygen. To hydrogen peroxide reduction, these two porphyrazines showed extremely low catalytic activity, which even shut off when each porphyrazine molecule was reduced by four electrons. Although no appreciable enhancement was achieved by using ion pair in oxygen and hydrogen peroxide reduction, the CoTmtppaCoTCPc ion pair had superior performance in catalyzing the oxidation of oxalate ion when compared with each individual moiety. |
