Co3O4 Nanoparticles Anchored on Selectively Oxidized Graphene Flakes as Bifunctional Electrocatalysts for Oxygen Reactions

Herein, we report the preparation of Co3O4 nanoparticles anchored on the surface of selectively oxidized graphene flakes with KMnO4 and O-3 - Co3O4@GF_KMnO4 and Co(3)O4@GF_O-3 nanocomposites - and the study of their electrocatalytic performance towards the oxygen reduction (ORR) and oxygen evolution reactions (OER). Both nanocomposites displayed ORR and OER electrocatalytic activity in alkaline medium. For ORR, onset potentials of 0.79V and 0.82V vs. RHE were achieved for Co3O4@GF_ KMnO4 and Co3O4@GF_O-3, respectively. Both nanocomposites presented excellent tolerance to methanol and, in the case of Co3O4@GF_O-3, a superior long-term stability with a current retention of 96.8% after 20 000s. For OER, the overpotential was 0.44 and 0.45V for Co3O4@GF_KMnO4 and Co3O4@GF_O-3, respectively. Additionally, Co3O4@GF_O-3 presented higher current densities, Faradaic efficiencies, and long-term stability (current loss of 32% after 15 000s). The superior bifunctional ORR/OER electrocatalytic activity displayed by Co3O4@GF_O-3 arises from the stronger chemical coupling between Co3O4 nanoparticles and specific oxygen surface groups of GF_O-3 flakes.