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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 Co3O4-CeO2/Co-N-C (ketjenblack carbon) catalysts were prepared by a facile method. The Co3O4 and CeO2 nanoparticles are uniformly anchored on the surface of Co and N doped carbon support. The half-wave potential of Co3O4-CeO2/Co-N-C in the rotating disk electrode testing is close to that of Pt/C. The Zn-air battery using Co3O4-CeO2/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 Co3O4, CeO2 and Co-N-C, the outstanding electrical conductivity and the large surface area. Benefitting from the high catalytic activity, environmental friendliness and the facile synthesis process, Co3O4-CeO2/Co-N-C catalyst lends itself well to a great prospect in the application of metal-air batteries. © 2020, Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature.

This work presents a desirable bifunctional catalyst - Co3O4 nanoparticles anchored on nitrogen-doped partially exfoliated multiwall carbon nanotubes (Co3O4/N-p-MCNTs) - for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for the rechargeable and flexible solid-state Zn-air battery. The Co3O4/N-p-MCNTs demonstrates good catalytic performance with the ORR half-wave potential of 0.760 V (vs RHE). Additionally, the Co3O4/N-p-MCNTs exhibits superior limiting current density with higher stability than Pt/C in alkaline solutions. The catalyst obtains a low operating potential (Ej10) of 1.62 V (vs RHE) to achieve a 10 mA cm-2 current density for OER. The potential difference (ΔE) between Ej10 of OER and ORR half-wave potential is 0.86 V, which is smaller than that of many highly active bifunctional catalysts reported recently. Moreover, a Zn-air battery utilizing Co3O4/N-p-MCNTs as the catalyst in cathode could successfully generate a specific capacity of 768 mAh g-1 at 10 mA cm-2, and there is no voltage loss after a continuous discharge of 135 h. The fabricated solid-state rechargeable Zn-air battery displays a high power density and superior long-term cycling stability. Furthermore, first-principles density functional theory simulations were conducted to explore the interfacial properties of the hybrid catalyst, hinting that the N-p-MCNTs could significantly enhance the electrical conductivity of Co3O4 nanoparticles. The free energy diagrams generated from our simulations suggest that the N-p-MCNTs influence the superior ORR performance, while cobalt oxide affects the favored performance of OER. The obtained results confirm that the Co3O4/N-p-MCNTs catalyst would have a broad impact and could be used for renewable energy conversion devices. © 2019 American Chemical Society.

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.

Rechargeable lithium metal anodes (LMAs) with long cycling life have been regarded as the "Holy Grail" for high-energy-density lithium metal secondary batteries. The skeleton plays an important role in determining the performance of LMAs. Commercially available copper foam (CF) is not normally regarded as a suitable skeleton for stable lithium storage owing to its relatively inappropriate large pore size and relatively low specific surface area. Herein, for the first time, we revisit CF and address these issues by rationally designing a highly porous copper (HPC) architecture grown on CF substrates (HPC/CF) as a three-dimensional (3D) hierarchically bicontinuous porous skeleton through a novel approach combining the self-assembly of polystyrene microspheres, electrodeposition of copper, and a thermal annealing treatment. Compared to the CF skeleton, the HPC/CF skeleton exhibits a significantly improved Li plating/stripping behavior with high Coulombic efficiency (CE) and superior Li dendrite growth suppression. The 3D HPC/CF-based LMAs can run for 620 h without short-circuiting in a symmetric Li/Li@Cu cell at 0.5 mA cm -2 , and the Li@Cu/LiFePO 4 full cell exhibits a high reversible capacity of 115 mAh g -1 with a high CE of 99.7% at 2 C for 500 cycles. These results demonstrate the effectiveness of the design strategy of 3D hierarchically bicontinuous porous skeletons for developing stable and safe LMAs.

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 N-doped 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.