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For rechargeable aqueous Zn-ion batteries (ZIBs), MnO2 is a desirable cathode material because of its structural diversity and high theoretical capacity of ~308 mA h g−1. MnO2 materials' poor cycle life and inferior conductivity, however, continue to be key obstacles to their application in ZIBs. These problems are anticipated to be resolved by developing a nanocomposite system consisting of MnO2 and a carbon-based matrix. Herein, a series of graphite carbon-coated δ-MnO2 nanoparticles (denoted as GC-δ-MnO2-X; X = 1, 2, and 3) for ZIB cathode materials is prepared via a feasible redox route and varying the amount of KMnO4 (7, 8, and 9 mmol). Benefiting from the abundant active sites and boosted Zn2+ ion diffusion rate, the GC-δ-MnO2-2 nanoparticles (8 mmol KMnO4) display excellent capacity of 299.6 mA h g−1 at 0.3 A g−1 with good cycle stability (62% capacity retention after 1500 cycles at 2 A g−1), surpassing that of the GC-δ-MnO2-1 (7 mmol KMnO4) and GC-δ-MnO2-3 (9 mmol KMnO4) samples. Moreover, the constructed quasi-solid-state ZIBs based on the GC-δ-MnO2-2 cathode show respectable capacity of 194.3 mA h g−1 at 0.3 A g−1, as well as outstanding safe properties. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) have great potential application in oxygen evolution reaction (OER). However, the inferior electrical conductivity and limited active sites of TMOs lead to their sluggish electrocatalytic efficiency. Herein, we adopted a two-step solvothermal approach to fabricate hierarchical CoO@NiO porous core–shell nanoarrays on carbon paper (denoted as CoO@NiO/CP). We found that numerous NiO nanofibers were uniformly coated over the surface of CoO nanosheets, forming a well-defined integrated interfacial nanocomposite. When acting as a catalyst for the OER, CoO@NiO/CP showed enhanced electroactivity with lower overpotential (323 mV at 10 mA cm−2), outstripping both pure CoO nanosheet array and NiO nanofiber array. Furthermore, it displayed outstanding OER stability, and the potential attenuation was only 3.4% after a 24 h chronopotentiometry test. The remarkable OER properties of CoO@NiO/CP were mainly due to its unique heterointerface between CoO and NiO, which promoted electron/charge transfer, increased electrocatalytic reactive sites, and improved electrical conductivity. Our presented findings provide a rational and practical interface-engineering approach for fabricating an advanced OER electrocatalyst. [ABSTRACT FROM AUTHOR]