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Herein, an effective strategy using defect engineering promoted by Ni atom doping on MnCo2O4 is proposed for bifunctional catalytic activities of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A series of NixMn1‐xCo2O4 with x=0, 0.1, 0.2, and 0.3 is hydrothermally synthesized. Tuning the electronic structure by Ni‐doped MnCo2O4 results in modulating the valence states by dominating Mn4+ / Co3+ with the increase of oxygen vacancies. At optimized Ni content, Ni0.2Mn0.8Co2O4 reveals activity toward ORR with a current density of −1.02 mA cm‐2 at 0.95 V (vs. RHE), a high electron transfer number of 3.536, and the highest half‐wave potential of 0.855 V, which is comparable to Pt/C. For OER, Ni0.2Mn0.8Co2O4 demonstrates the lowest overpotential of 503 mV to achieve a current density of 10 mA cm−2. Additionally, rechargeable zinc‐air batteries (RZABs) with Ni0.2Mn0.8Co2O4 catalyst demonstrate a capacity of 808.6 mA h g−1 at 1.0 mA cm−2 with power densities of 459 mW cm−2 at 675 mA cm−2. The improved binding strength (Mn−O/Co−O bond) and the enhanced stability by Ni atom doping in MnCo2O4 for ORR/OER is proved by ex‐situ FT‐EXAFS. This work highlights defect engineering on Ni‐doped MnCo2O4 used as bifunctional ORR/OER catalysts for high‐performance RZABs. [ABSTRACT FROM AUTHOR]

Manganese oxide (MnO2) is one of the most promising intercalation cathode materials for zinc ion batteries (ZIBs). Specifically, a layered type delta manganese dioxide (δ-MnO2) allows reversible insertion/extraction of Zn2+ ions and exhibits high storage capacity of Zn2+ ions. However, a poor conductivity of δ-MnO2, as well as other crystallographic forms, limits its potential applications. This study focuses on δ-MnO2 with nanoflower structure supported on graphite flake, namely MNG, for use as an intercalation host material of rechargeable aqueous ZIBs. Pristine δ-MnO2 nanoflowers and MNG were synthesized and examined using X-ray diffraction, electron spectroscopy, and electrochemical techniques. Also, performances of the batteries with the pristine δ-MnO2 nanoflowers and MNG cathodes were studied in CR2032 coin cells. MNG exhibits a fast insertion/extraction of Zn2+ ions with diffusion scheme and pseudocapacitive behavior. The battery using MNG cathode exhibited a high initial discharge capacity of 235 mAh/g at 200 mA/g specific current density compared to 130 mAh/g which is displayed by the pristine δ-MnO2 cathode at the same specific current density. MNG demonstrated superior electrical conductivity compared to the pristine δ-MnO2. The results obtained pave the way for improving the electrical conductivity of MnO2 by using graphite flake support. The graphite flake support significantly improved performances of ZIBs and made them attractive for use in a wide variety of energy applications. [ABSTRACT FROM AUTHOR]