π-Extended nonplanar cobalt porphyrins immobilized on MWCNTs as efficient electrocatalysts for selective oxygen reduction reaction

Abstract

Two π-extended cobalt porphyrins are synthesized and one of them is crystallographically characterized. The nanocomposites of nonplanar (curved) porphyrin immobilized multi-walled carbon nanotubes were thoroughly characterized spectroscopically and microscopically, showing ∼200 mV positive shift in the O₂ reduction peak potential in aqueous media and ∼100 mV shift in the onset potential of the O₂ reduction relative to the control meso-tetraphenylporphyrinatocobalt(II) nanocomposite. Both the π-extended cobalt porphyrin immobilized nanocomposites efficiently catalyze selective 4e⁻/4H⁺ O₂ reduction under ambient conditions with excellent methanol tolerance and high stability due to effective π–π interactions, and could be an alternative for expensive Pt-based cathode materials in fuel cells.