An amorphous trimetallic (Ni–Co–Fe) hydroxide-sheathed 3D bifunctional electrode for superior oxygen evolution and high-performance cable-type flexible zinc–air batteries†
Abstract
The emerging flexible/wearable electronics have greatly stimulated research on portable batteries with high specific energy and excellent mechanical properties. State-of-the-art zinc–air batteries (ZABs) are potential candidates for flexible energy supply; however, their development is hindered by the sluggish kinetics of the oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) of an air cathode. Herein, we demonstrate a 3D integrated bifunctional oxygen electrode of NiCo2O4@NiCoFe–hydroxide nanoarrays for flexible all-solid-state ZABs. Owing to the intact mesoporous nanoarrays synergized with the amorphous trimetallic hydroxide sheath, the free-standing NiCo2O4@NiCoFe–hydroxide electrode exhibited excellent bifunctional activities with an ultralow potential difference of 695 mV between OER and ORR. The NiCo2O4@NiCoFe–hydroxide-based planar aqueous ZAB achieved high discharge capacity (723 mA h gzinc−1 at 10 mA cm−2), high energy density (864.2 W h kgzinc−1 at 5 mA cm−2) and long cycle life of up to 250 h. More significantly, cable-type all-solid-state ZABs fabricated with the 3D oxygen electrode demonstrated an impressive volumetric energy density of 38.1 mW h cm−3 and high mechanical flexibility even after 2000 bending cycles, highlighting their enormous potential for flexible/wearable energy applications.
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