The synthesis and characterization of a Co-N/C composite catalyst for the oxygen reduction reaction in acidic solution

A non-precious metal Co-N/C catalyst for the oxygen reduction reaction (ORR) was synthesized by heating a mechanical mixture of cobalt chloride, urea and acetylene black under a nitrogen atmosphere. The catalyst was characterized by XRD and XPS. The electrocatalytic activity in the ORR was evaluated by linear sweep voltammetry in 0.5 mol L⁻¹ H₂SO₄ solution. The results show that the Co-N/C catalyst aids the reduction of oxygen. The presence of elemental cobalt in the precursor allows nitrogen atoms to embed themselves in the graphite matrix to form pyridinic and graphitic type C-N structures as the ORR active sites. The effect of heat-treating temperature on the catalytic activity was also investigated. The results also show that the Co-N/C catalyst is most active when pyrolyzed at 600°C. The obtained Co-N/C catalyst loses some activity after initial exposure to the H₂SO₄ solution because of leaching, but is then stable for up to 20 h immersion. The catalyst is also stable when charged, which is supported by the cyclic voltammetry results.