One-pot synthesis of self-supported hierarchical urchin-like Ni3S2 with ultrahigh areal pseudocapacitance

Recently, nickel sulfides have been widely investigated as an electrode material for pseudocapacitors. Among them, self-supported nickel sulfides have been intensively studied; yet, their structures are rather limited to nanosheet or nanorod arrays. Herein, a facile one-step hydrothermal method was developed to synthesize self-supported Ni3S2 on a Ni foam substrate with an urchin-like hierarchical structure consisting of nanowire subunits with a diameter of about 20-30 nm, thus combining the advantages of both hierarchical and self-supported structures. Because of this unique structure, when the sample was applied as an electrode for supercapacitors, it demonstrated an ultrahigh areal capacitance of 21.54 F cm(-2) at a current rate of 2 mA cm(-2), and even at a very high current rate of 50 mA cm(-2), a reversible capacitance of 5.40 F cm(-2) can still be retained after 1000 charge-discharge cycles. When the sample was employed as the cathode to build an asymmetric supercapacitor (ASC) with activated carbon as the anode, the device exhibited an areal capacitance of 1.26 F cm(-2) at a current rate of 2 mA cm(-2) and a coulombic efficiency of 97.7%. Furthermore, this device showed great potential for practical application by lighting up 8 red light-emitting diodes.