Highly\nHierarchical Porous Ultrathin Co₃O₄ Nanosheets@Ni\nFoam for High-Performance Supercapacitors

Abstract

Rational\ndesign and preparation of transitional-metal-oxide-based\nbattery-type materials possessing comprehensive merits for supercapacitors\nhave attracted extensive attention due to the high theoretical specific\ncapacity and energy density. Herein, we demonstrate the general fabrication\nof ultrathin-nanosheet-structured transitional-metal oxides on Ni\nfoam via a facile hydrothermal synthesis with the assistance of formamide.\nUsing poly­(vinyl pyrrolidone) (PVP) as a directing agent, we can generate\nultrathin Co₃O₄ nanosheets with a highly hierarchical\nporous structure on the Ni foam (denoted as P-Co₃O₄-ns@NF), which is favorable for fast and deep diffusion of\nelectrolyte and helps to effectively enhance its electrochemical performances.\nBenefiting from the integrated superiorities, the present P-Co₃O₄-ns@NF could deliver a high specific capacity\nof 1196.5 mC·cm^–2 at 5 mA·cm^–2 (798 C·g^–1 at ca. 3.3 A·g^–1) and a long life span with 107% specific capacity retention after\n5000 cyclic charge/discharge runs. The asymmetric supercapacitor constructed\nby P-Co₃O₄-ns@NF and activated carbon could\nexhibit high energy density (51.7 Wh·kg^–1at\n1125 W·kg^–1) and remarkable cycling stability\n(with the capacitance retention of 91.8% after 15 000 cycles).\nThese results indicate that the as-prepared highly hierarchical porous\nnanocomposite is a promising material for high-performance supercapacitors.