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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 MnO quantum dots (QDs, ca. 2 nm) anchored on nitrogen-doped partially exfoliated multiwall carbon nanotubes (MnO QDs/N-p-MCNTs) as a high-performance ORR catalyst. The MnO 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 MnO QDs/N-p-MCNTs demonstrated superior stability than Pt/C in alkaline solutions. Furthermore, a Zn-air battery using the MnO QDs/N-p-MCNTs cathode catalyst successfully generated a specific capacity of 745 mA h g at 10 mA cm without the loss of voltage after continuous discharging for 105 h. The superior ORR activity of MnO QDs/N-p-MCNTs can be ascribed to the homogeneous MnO QDs loaded onto the N-doped carbon skeleton and the synergistic effects of MnO 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 O, at the interface between MnO 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 MnO QDs/N-p-MCNTs is low, which will broadly facilitate the real application of metal-air batteries.

Zinc-air battery is one of the most promising next-generation energy conversion and storage systems. Green and low-cost catalysts with high oxygen reduction reaction (ORR) catalytic activity are desired to meet the requirements of Zinc-air batteries. Herein, poly-active centric Co 3 O 4-CeO 2 / CoN -C (ketjenblack carbon) catalysts were prepared by a facile method. The Co 3 O 4 and CeO 2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support. The half-wave potential of Co 3 O 4-CeO 2 /Co-N-C in the rotating disk electrode testing is close to that of Pt/C. The Zn-air battery using Co 3 O 4-CeO 2 /Co-N-C as the cathode catalyst can provide a high specific capacity of 728 mA h g −1 at 20 mA cm −2 and maintain a stable discharge voltage. The remarkable catalytic performance is mainly attributed to the synergistic effect among Co 3 O 4 , CeO 2 and CoN -C, the outstanding electrical conductivity and the large surface area. Benefitting from the high catalytic activity, environmental friendliness and the facile synthesis process, Co 3 O 4-CeO 2 /Co-N-C catalyst lends itself well to a great prospect in the application of metalair batteries.

AP65 with strong discharge activity is an attractive magnesium anode used for high-power seawater activated batteries. Herein, we adopt multi-pass rolling to tailor the microstructure of AP65 and systematically study the effect of rolling reduction on its discharge and corrosion behaviour. The results indicate that 63% reduction uniformly refines the grains and favours the formation of nanometer subgrains that distribute homogeneously in the magnesium matrix, hence promoting the active dissolution of the AP65 plate at 180 mA cm À2 and leading to its more negative discharge potential along with higher anodic efficiency compared with other samples. Furthermore, the microstructure features corresponding to different rolling reductions and their impacts on the electrochemical response of AP65 are also analyzed.rsc.li/rsc-advances 53226 | RSC Adv., 2017, 7, 53226-53235This journal is