Alkali conversion of Ni-Co nanoarrays on carbon cloth for a high-capacity supercapacitor electrode

Three-dimensional free-standing nanoarray electrodes with hierarchical structure grown on carbon cloth substrate have attracted great interest for flexible energy storage devices. However, the direct growth of active material with a large mass loading on carbon fibers is difficult because of the hydrophobic nature. Herein, "two-step" growth route is adopted to achieve high-loading Ni-Co carbonate hydroxide nanowire arrays, in which the effect of electrochemical pre-activation is discussed. A facile and novel process is used to boost the areal capacity by converting Ni-Co carbonate hydroxide nanowires to hydroxide nanowire-supported nanoplate arrays in an alkaline solution. The areal capacity of the as-soaked free-standing Ni-Co hydroxide nanoarrays electrode increases from 856 mC.cm (2) (152 C.g(-1)) to 1944 mC.cm (2) (348 C.g(-1)) and 3028 mC.cm (2) (542 C.g (1)) at 2 mA.cm (2) after soaking for 8 h and 16 h. The electrochemical pre-activation is important for achieving high mass loading as well as high rate capability. Moreover, the as-soaked electrode is employed as the positive electrode for hybrid supercapacitor. The device possesses a high areal capacitance of 1.47 F.cm (2) at 1 mA.cm (2), a large energy density of 6.7 mWh.cm (3) at 11.6 mW.cm (3). This work gives an insight for designing high-loading three-dimensional electrodes and paves a new way to construct binder-free film electrode for highperformance hybrid supercapacitor applications. (C) 2017 Elsevier Ltd. All rights reserved.