MnCo2O4/N-doped graphene quantum dot vigorously coupled to MXene nanosheet: A bifunctional Oxygen electrocatalyst outperforms Pt/IrO2 benchmark electrocatalysts in metal-air batteries

The rational design and fabrication of a high performance, durable, and cost effective bifunctional electrocatalyst employed for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of remarkably great importance for the commercialization of rechargeable metal–air batteries. While electrocatalysts designed based on spinel oxides have been deemed as promising catalyst materials for the ORR and OER, their catalytic performance still must be considerably enhanced to satisfy the prerequisites of practical applications. In this work, a heterostructure (MnCo2O4/N-GQD/MXene) of Ti3C2Tx (MXene) nanosheets decorated with spinel manganese-cobalt oxide (MnCo2O4) nanoparticles and N-doped-graphene quantum dots(N-GQD) fabricated via facile hydrothermal method. The presence of plentiful active reaction sites, high surface area and distinctive electronic structure, resulting from robust interfacial interaction, lead to the higher electron conductivity and faster ORR/OER kinetics in Zn-air batteries. Therefore, the obtained MnCo2O4/N-GQD/MXene electrocatalyst presenting an outstanding ORR performance with a low over potential of only 22 mV, half-wave potential (E1/2) of 0.87 V (vs RHE), and remarkable long-term durability, strikingly outperforms commercial Pt/C (20 % w/w). Concerning OER, the MnCo2O4/ N-GQD/MXene exhibiting an onset potential of 1.54 V(vs RHE) and a Tafel slope of 65 mV dec−1 displays better performance than IrO2. The zinc-air battery with MnCo2O4/ N-GQD/MXene cathode shows superior peak power density (152.8 mW cm−2), tremendous capacity efficiency up to 753 mAh g−1 and substantial stability, proving that MnCo2O4/ N-GQD/MXene could feasibly be used in metal–air batteries.