Hierarchical NiSe@Co2(CO3)(OH)2 heterogeneous nanowire arrays on nickel foam as electrode with high areal capacitance for hybrid supercapacitors

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To meet the demand for ever-increasing energy storage and conversion, it is most important to fabricate high-performance electrodes by matching the electrode materials to nanostructural design. In this research, for the first time, unique hierarchical NiSe@Co2(CO3)(OH)2 heterogeneous nanowire arrays were successfully constructed onto the nickel foam by a simple two-step soft-chemical approach for application as electrodes of supercapacitors. NiSe nanowires with superior conductivity were designed for builting in situ onto the Ni foam to exert their electrochemical properties, and more importantly, to serve as a bridge for high-speed electron transport between the electroactive material and the current collector. Furthermore, Co2(CO3)(OH)2 nanowires were horizontally constructed onto a vertical NiSe precursor to form a 1-D heterostructure, which provided more electrochemically active sites and significantly increased the space utilization of the current collector surface. In particular, abundant pores and heterogeneous interfaces existed in the heterogeneous network that were composed of interlaced nanowires, which worked well with the inherently superior conductivity of the selenide material to provide a fast dual-channel for electrolyte penetration and electron transportation. Moreover, the hierarchical electrode achieved an outstanding areal specific capacitance of 9.56 F cm−2 (at 4 mA cm−2) and a rare capacitance retention of 68.1% (current density increased from 4 to 80 mA cm−2). A hybrid supercapacitor of NiSe@Co2(CO3)(OH)2//AC was assembled and exhibited competitive energy density and power density, confirming its potential as a promising electrode for next-generation electrochemical energy storage.