Rechargeable zinc (Zn)–air batteries receive research interest due to the high theoretical energy density, intrinsic safety, and excellent market competition. The design of the triple‐phase (solid/liquid/gas) boundaries of the air electrode is the key to excellent performance. Although integrated air electrodes ensure the large active sites, rapid electron and species transport, and good stability during the long‐term operation, the massive agglomeration of hydrophobic binder always leads to the reduction of triple‐phase boundaries using conventional fabrication strategies. To address this issue, a novel strategy for constructing the triple‐phase boundaries of an integrated Co3O4 electrode is proposed through hydrothermal treatment under a high temperature. The ultrasmall hydrophobic particles distribute extremely uniformly in Co3O4 nanowires, which do not cover the electrode surface and create good gas‐phase boundaries, leading to a high‐performance Zn–air battery with a high discharge voltage of 1.13 V and a low charge voltage of 2.06 V at even 10 mA cm−2, a high peak power density of 51.7 mW cm−2, and a small voltage gap increment of only 86 mV after 1000 cycles. This strategy greatly enhances the performance and durability of integrated air electrodes, raising the attention to boundary design for other electrochemical energy conversion and storage devices.
Developing
oxygen electrocatalysts with outstanding activity and
low cost is vital to the promotion of the oxygen reduction reaction
(ORR) and oxygen evolution reaction (OER) of Zn–air batteries.
Herein, an NiCo2O4 nanoparticle-decorated nitrogen-doped
graphene nanosheet (NiCo2O4/N-G) is synthesized
as a bifunctional electrocatalyst. The ultrasmall NiCo2O4 nanoparticle with an average particle size of 4 nm
can introduce plentiful reaction active sites. Furthermore, the N-G
nanosheets with small dimensions of 200 nm possess an extremely large
specific surface area and can effectively restrict the aggregation
of NiCo2O4 nanoparticles and promote species
transport. Compared with NiCo2O4 and N-G, NiCo2O4/N-G exhibits a higher ORR and OER electrocatalytic
activity in alkaline electrolytes, and it demonstrates almost comparable
ORR activity but superior stability to commercial Pt/C. Using the
NiCo2O4/N-G catalyst, a home-built Zn–air
battery demonstrates a peak power density of 108.3 mW cm–2, an excellent discharge capacity of up to 792.6 mAh gZn
–1, and a superior energy density of up to 879.9
Wh kg. Moreover, stable charge–discharge voltage gaps and an
energy efficiency of ∼63% at 10 mA cm–2 can
sustain for over 540 cycles during cycling, indicating excellent cycling
stability.
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