Co(ii)-porphyrin-decorated carbon nanotubes as catalysts for oxygen reduction reactions: an approach for fuel cell improvement

Abstract

The development of high-performance and cost-effective catalysts for the oxygen reduction reaction (ORR) is essential for the advancement of fuel cells. In this work, three different functionalized cobalt porphyrins, meso-tetraphenylporphyrinatocobalt(II) (CoTPP), meso-tetrakis(4′-hydroxyphenyl)porphyrinatocobalt(II) (CoTHPP) and meso-tetrakis(4′-carboxy-phenyl)porphyrinatocobalt(II) (CoTCPP), are prepared. These porphyrins are immobilized non-covalently on multiwalled carbon nanotubes (MWCNTs) and used for the ORR in 0.1 M HClO₄, 0.1 M phosphate buffer solution (pH 7.0) and 0.1 M KOH media. The composite materials are characterized by using spectroscopic and electrochemical techniques and their oxygen reduction efficiencies are compared in different media. Kinetic interpretations and hydrodynamic voltammetry (in three media) studies demonstrated that the MWCNT–CoTPP, MWCNT–CoTHPP and MWCNT–CoTCPP composite materials exhibit significant efficiency with decreased overpotential, considerable methanol tolerance and long term operational stability (up to 3000 cycles) for the ORR similar to commercially available platinum carbon (Pt–C) catalysts. These results reveal that the new MWCNT–cobalt porphyrin composite materials can be a potential alternative to the expensive Pt–C catalysts or other commercial cathode materials in fuel cells.