Cobalt Porphyrin Functionalized Carbon Nanotubes for Oxygen Reduction

Carbon nanotube (CNT) compns. were prepd. by covalently grafting a Co(II) porphyrin to functionalized multiwalled carbon nanotubes (MWCNTs) via zwitterionic functionalization of the CNT sidewalls followed by a SN2 substitution reaction. The MWCNT-Co-porphyrin compns., mixed with Nafion, displayed excellent catalytic performance for oxygen redn. in acidic media (pH = 0.0-5.0) at room temp. With low catalyst loading, the oxygen redn. rates achieved are more than one order of magnitude higher than previously reported values for similar Co-porphyrin catalysts. These results demonstrate the advantages of systems of MWCNTs covalently linked to electrocatalytic mols. The electrodes are easily fabricated by a drop-casting vacuum drying procedure. Rotating disk electrode and rotating ring disk electrode measurements revealed the mechanism to be a direct four-proton and four-electron redn. of oxygen to water. These results demonstrate that new MWCNT electrocatalytic systems are potential substitutes for platinum or other metal-based cathode materials in proton conducting membrane fuel cells. [on SciFinder(R)]