Highly Hierarchical Porous Ultrathin Co₃O₄ Nanosheets@Ni Foam for High-Performance Supercapacitors

Rational design and preparation of transitional-metal-oxide-based battery-type materials possessing comprehensive merits for supercapacitors have attracted extensive attention due to the high theoretical specific capacity and energy density. Herein, we demonstrate the general fabrication of ultrathin-nanosheet-structured transitional-metal oxides on Ni foam via a facile hydrothermal synthesis with the assistance of formamide. Using poly(vinyl pyrrolidone) (PVP) as a directing agent, we can generate ultrathin Co3O4 nanosheets with a highly hierarchical porous structure on the Ni foam (denoted as P-Co3O4-ns@NF), which is favorable for fast and deep diffusion of electrolyte and helps to effectively enhance its electrochemical performances. Benefiting from the integrated superiorities, the present P-Co3O4-ns@NF could deliver a high specific capacity of 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 5000 cyclic charge/discharge runs. The asymmetric supercapacitor constructed by P-Co3O4-ns@NF and activated carbon could exhibit high energy density (51.7 Wh·kg–1at 1125 W·kg–1) and remarkable cycling stability (with the capacitance retention of 91.8% after 15 000 cycles). These results indicate that the as-prepared highly hierarchical porous nanocomposite is a promising material for high-performance supercapacitors.