Graphene-Enhanced Oxygen Reduction by MN4Type Cobalt(III) Catalyst

A nanocomposite of a dichloro-amido-macrocyclic cobalt(III) complex ( 1 ) and graphene was developed and characterized using various microscopic and spectroscopic techniques such as X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy and Raman spectroscopy. The nanocomposite was evaluated for electrocatalytic activity toward oxygen reduction reaction (ORR) in fuel cell applications. This complex ( 1 ) showed efficiency in a wide range of pH (acidic and basic) conditions for successful ORR. Apart from pH studies, the ratio of electrocatalyst 1 to graphene was varied for developing the optimal ORR catalyst. The use of graphene as a carbon support along with 1 in ORR studies not only resulted in increased current density but also a positive shift of the reduction potential by 140 mV (with respect to the Ag/AgCl reference electrode). Investigation of the catalytic mechanism using rotating disk electrode and rotating ring-disk electrode studies revealed its mechanism in acidic and basic conditions. The ORR was found to be a four-electron process in both pH conditions. The rate constant of ORR activity was found to be 3.85 × 10 5 mol –1 s –1 at pH 2.0. The efficiency of the nanocomposite in ORR indicates the advantage of using both 1 and graphene for fuel cell applications.