Hierarchical construction of core–shell metal oxide nanoarrays with ultrahigh areal capacitance

High areal capacitance of electrodes is highly desirable for practical supercapacitor applications, which requires a combination of high mass-loading and high utilization of electrochemically active material. In this work, we report the fabrication of hierarchical core–shell Co3O4@NiO [email protected] arrays where ultrathin NiO nanorods (~5 nm) were directly grown on the Co3O4 nanowire arrays via a two-step hydrothermal reaction followed by a calcination process. The hybrid nanoarrays exhibited a high specific capacitance of 2033 F g−1 at the current density of 5 mA cm−2 along with a mass loading as high as 19.5 mg cm−1, leading to an ultrahigh areal capacitance of 39.6 F cm−2 as a supercapacitor electrode, much higher than that of pure Co3O4 nanowire arrays (6.7 F cm−2). In addition, a remarkable rate capability (21.4 F cm−2 at the current density of 30 mA cm−2) and excellent cycling stability (100% after 1000 cycles) were observed. Compared with the pure Co3O4 nanowire arrays, the greatly enhanced capacitive performance is mainly attributed to the unique hierarchical porous architecture and the synergistic effect of the individual components.