Carbon dots bridge NiO and Mn2O3 as highly efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries

Abstract

The development of high-efficiency, low-cost and durable bifunctional oxygen electrocatalysts is of great significance for the large-scale application of rechargeable zinc-air batteries. Herein, the carbon dots bridging nickel oxide and manganese trioxide through the oxygen-containing group of carbon dots (NiO-Mn2O3-CDs) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is proposed. The optimal NiO-Mn2O3-CDs yields remarkable electrocatalytic activity with low overpotential (298 mV) to derive the 10 mA·cm−2 for OER and a high half wave potential (0.84 V vs. RHE) for ORR. The outstanding performances are attributed to the CDs covalently bridging Ni and Mn atoms, which reprogram the electronic structure of active sites and enhance charge transfer. Consequently, the rechargeable zinc-air battery test with NiO-Mn2O3-CDs as the air cathode deliver the excellent performances, including a high open voltage (1.51 V), a maximum power density (287 mW∙cm−2 @ 0.35 A∙cm−2) and robust cycling life, outperforming the commercial Pt/C + IrO2. This work presents an efficient strategy to construct the highly active and stability bifunctional air cathodes for electrochemical energy devices.