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

Abstract

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 high-performance hybrid supercapacitor applications.