Mn3O4 Quantum Dots Supported on Nitrogen-Doped Partially Exfoliated Multiwall Carbon Nanotubes as Oxygen Reduction Electrocatalysts for High-Performance Zn-Air Batteries

Highly efficient and low-cost nonprecious metal

electrocatalysts that favor a four-electron pathway for the oxygen

reduction reaction (ORR) are essential for high-performance metal−

air batteries. Herein, we show an ultrasonication-assisted synthesis

method to prepare Mn3O4 quantum dots (QDs, ca. 2 nm) anchored

on nitrogen-doped partially exfoliated multiwall carbon nanotubes

(Mn3O4 QDs/N-p-MCNTs) as a high-performance ORR catalyst.

The Mn3O4 QDs/N-p-MCNTs facilitated the four-electron pathway

for the ORR and exhibited sufficient catalytic activity with an onset

potential of 0.850 V (vs reversible hydrogen electrode), which is only

38 mV less positive than that of Pt/C (0.888 V). In addition, the

Mn3O4 QDs/N-p-MCNTs demonstrated superior stability than Pt/

C in alkaline solutions. Furthermore, a Zn−air battery using the

Mn3O4 QDs/N-p-MCNTs cathode catalyst successfully generated a

specific capacity of 745 mA h g−1 at 10 mA cm−2 without the loss of voltage after continuous discharging for 105 h. The

superior ORR activity of Mn3O4 QDs/N-p-MCNTs can be ascribed to the homogeneous Mn3O4 QDs loaded onto the Ndoped

carbon skeleton and the synergistic effects of Mn3O4 QDs, nitrogen, and carbon nanotubes. The interface binding energy

of −3.35 eV calculated by the first-principles density functional theory method illustrated the high stability of the QD-anchored

catalyst. The most stable adsorption structure of O2, at the interface between Mn3O4 QDs and the graphene layer, had the

binding energy of −1.17 eV, greatly enhancing the ORR activity. In addition to the high ORR activity and stability, the cost of

production of Mn3O4 QDs/N-p-MCNTs is low, which will broadly facilitate the real application of metal−air batteries.