Facile synthesis of nickel–cobalt binary oxides with controllable morphology as high-performance electrode materials for asymmetric charge storage device

Vertical nanowall architectures of nickel–cobalt binary oxides with rich oxygen vacancies have been meticulously designed and successfully synthesized on nickel foam (denoted as NiCo0.7Ox@NF) via a one-step hydrothermal route followed by annealing. The morphology can be easily controlled by adjusting the ratio of sodium dodecyl sulfate (SDS), and the dependence of electrochemical performance on the ratio of SDS was investigated. The NiCo0.7OX@NF-0.9 electrode exhibits optimal electrochemical performance at molar ratio of nickel:SDS = 1:0.9, including high specific capacitance (2820.0 F g−1 (1329.0 C g−1) at the current density of 1 A g−1), excellent rate performance (2137.6 F g−1 (960.3 C g−1) at high current density of 20 A g−1), and superior cycling stability (86% capacitance retention after 5000 cycles at 20 A g−1). Furthermore, the asymmetric supercapacitor NiCo0.7Ox@NF-0.9//AC@NF device, fabricated using NiCo0.7Ox@NF-0.9 and activated carbon at nickel foam (AC@NF) as the positive and negative materials, respectively, exhibit a maximum energy density of 85.01 Wh kg−1 at 900 W kg−1, and even at high power density of 17,996 W kg−1 the energy density can be retained at 46.35 Wh kg−1. These results indicate that the unique architecture and abundant oxygen vacancies in NiCo0.7Ox@NF-0.9 electrode can greatly enhance the electrochemical properties. This study provided a facile method to synthesize a high-performance pseudocapacitive supercapacitor electrode, which is of great significance for the research of electrochemical energy storage and conversion.