ELECTROCHEMICAL AND ELECTROCATALYTIC PROPERTIES OF COBALT TETRA-2,3-PYRIDOPORPHYRAZINE IN AQUEOUS-SOLUTIONS

Cyclic voltammetry and a ring-disk electrode were used to study the re dox changes and electrocatalytic properties in cathodic oxygen reducti on of cobalt tetra-2,3-pyridoporphyrazine (CoPPz: the tetraaza analog of cobalt phthalocyanine) deposited on acetylene black (AB) over a wid e range of pH in aqueous solutions. The redox changes occurring at the AB/CoPPz surface gave rise to two reversible maxima due to the oxidat ion and reduction of the central ion: Co (2+) reversible Co (1+), and to oxidation and reduction of the organic ligand. The ability of CoPPz to undergo protonation in media of moderate acidity greatly facilitat ed these processes. Three electrons were involved in oxygen electrored uction at CoPPz at pH < 1.5; at pH between 1.5 and 5 the value of n wa s 3.5-3.7; at 5 < pH < 12 the value of n was four. It was shown that C oPPz activates the electroreduction of H2O2. The influence of proton-a cceptor properties of the catalyst on its electrochemical and electroc atalytic properties was discussed.