Co-CoO-Co3O4/N-doped carbon derived from metal-organic framework: The addition of carbon black for boosting oxygen electrocatalysis and Zn-Air battery

Abstract

Electrocatalysts with high activity toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential and desired for metal-air batteries, fuel cells, water-splitting and CO2 reduction. Here, a series of Co-CoxO/N-doped Carbon (NC) is developed as bifunctional electrocatalysts via the pyrolysis of a simple physical mixture of cobalt-based metal-organic framework (MOF) and carbon black (CB). The obtained electrocatalysts exhibit considerably enhanced bifunctional activity as compared to the pure MOF derived counterpart. The essential roles of added CB in boosting the bifunctional activity are investigated. With the addition of CB, the surface concentrations of active pyridinic-N and graphitic-N for ORR and the surface CoIII/CoII ratios for OER are increased. Furthermore, the charge transfer efficiency and the electrochemically active surface areas (ECSAs) are also enhanced for the resulting electrocatalyst. The optimized Co-CoO-Co3O4/NC exhibits excellent bifunctional activity and durability, surpassing the commercial 20 wt% Pt/C (for ORR) and IrO2 (for OER). When applied in an air electrode, the corresponding Zn-air battery with Co-CoO-Co3O4/NC presents the better performance than that with 20 wt% Pt/C.