OXYGEN REDUCTION ON MONOMERIC TRANSITION-METAL PHTHALOCYANINES IN ACID ELECTROLYTE

The characteristics of oxygen reduction on high surface-area carbon supported metallophthalocyanines have been studied in 8 N H2SO4 and also in 6 N KOH. Catalysts were prepared by the usual H2SO4-precipitation method or by adsorption from pyridine solution. The order of activity in both electrolytes is: Fe > Co ≈ Ru > Mn > Pd ≈ Pt > Zn. It was found that basic surface groups have a beneficial effect on the activity of CoPc/C. A heat treatment in N2 or Ar atmosphere at temperatures up to 800°C enhances the stability and activity of CoPc/C, the activity of RuPc/C and the stability of FePc/C. Some electrocatalytic aspects are discussed; it is shown that FePc, CoPc and RuPc are real oxygen reduction catalysts in H2SO4. The activity of CoPc/C is proportional to CoPc loading, but the activity of FePc/C seems to be determined by a small fraction of the FePc present. The oxygen reduction and H2O2 decomposition activities are found to be correlated. For CoPc/C the first electron transfer seems to be rate-limiting in H2SO4; in KOH the second electron transfer seems to be rate-limiting in all cases. © 1979.