Temperature dependent substrate-free facile synthesis for hierarchical sunflower-like nickel-copper carbonate hydroxide with superior electrochemical performance for solid state asymmetric supercapacitor

Here, we demonstrate a facile and substrate-free synthesis of sunflower-like nickel-copper carbonate hydroxide (NC) as electrode material for supercapacitor application, employing a polypyrrolidone assisted hydrothermal protocol. The temperature of the hydrothermal reaction is optimized to achieve high specific surface area with superior electrochemical properties of NC. Owing to the existence of enormous mesopores with high specific surface area (128.6 m(2) g(-1)), the sunflower-like NC exhibits a high specific capacitance (Csp) value of 1185.9 F g(-1) at 1 A g(-1) with 93.1% initial Csp retention even after 5000 successive galvanostatic charge-discharge (GCD) cycles. Furthermore, an asymmetric device is assembled using this sunflower-like NC as positive and activated carbon as negative electrode with a poly(vinyl alcohol)-potassium hydroxide (PVA-KOH) gel electrolyte membrane as a separator. This work displays the first example of sunflower like nickel copper carbonate hydroxide for the fabrication of ASC device that displays maximum of 32.7 Wh kg(-1) energy density, 359.9 W kg(-1) power density at 0.6 A g(-1) with excellent cyclic stability (88.8% retention after 5000 GCD cycles). The features efficaciously illustrate great prospective of our high performance ASC device for advance electronic applications.