Designed\nFormation of Co₃O₄/NiCo₂O₄ Double-Shelled Nanocages with Enhanced Pseudocapacitive\nand Electrocatalytic Properties

Abstract

Hollow\nstructures with high complexity in shell architecture and\ncomposition have attracted tremendous interest because of their great\nimportance for both fundamental studies and practical applications.\nHerein we report the designed synthesis of novel box-in-box nanocages\n(NCs) with different shell compositions, namely, Co₃O₄/NiCo₂O₄ double-shelled nanocages (DSNCs).\nUniform zeolitic imidazolate framework-67/Ni–Co layered double\nhydroxides yolk-shelled structures are first synthesized and then\ntransformed into Co₃O₄/NiCo₂O₄ DSNCs by thermal annealing in air. Importantly, this strategy\ncan be easily extended to prepare other complex DSNCs. When evaluated\nas electrodes for pseudocapacitors, the Co₃O₄/NiCo₂O₄ DSNCs show a high specific capacitance\nof 972 F g^–1 at a current density of 5 A g^–1 and excellent stability with 92.5% capacitance retention after 12 000\ncycles, superior to that of Co₃O₄ NCs with simple\nconfiguration and Co₃O₄/Co₃O₄ DSNCs. Besides, the Co₃O₄/NiCo₂O₄ DSNCs also exhibit much better electrocatalytic\nactivity for the oxygen evolution reaction than Co₃O₄ NCs. The greatly improved electrochemical performance of\nCo₃O₄/NiCo₂O₄ DSNCs demonstrates\nthe importance of rational design and synthesis of hollow structures\nwith higher complexity.