Ionic liquid modified graphene nanosheets anchoring manganese oxide nanoparticles as efficient electrocatalysts for Zn-air batteries

Abstract

Ionic liquid (IL) modified reduced graphene oxide (rGO-IL) nanosheets anchoring manganese oxide (Mn3O4) are synthesized via a facile solution-based growth mechanism and applied to a Zn-air battery as an effective electrocatalyst for the oxygen reduction reaction (ORR). In this study, the IL moiety in these composites increases not only the conductivity of the system, but also the electrocatalytic activity compared to pristine rGO, together with the synergic effect of facilitating the ORR with the intrinsic catalytic activity of Mn3O4. Based on the Koutecky-Levich plot, we suggest that the ORR pathway of these composites is tunable with the relative amount of Mn3O4 nanoparticles supported onto the graphene sheets; for example, the ORR mechanism of the system with a lower Mn3O4 (19.2%) nanoparticle content is similar to a Pt/C electrode, i.e., a one-step, quasi-4-electron transfer, unlike that with a higher Mn3O4 (52.5%) content, which undergoes a classical two-step, 2-electron pathway. We also demonstrate the potential of these hybrid rGO-IL/Mn3O4 nanoparticles as efficient catalysts for the ORR in the Zn-air battery with a maximum peak power density of 120 mW cm(-2); a higher performance than that from commercial cathode catalysts.