Ni and Zn co-substituted Co(CO₃)_0.5OH self-assembled flowers array for asymmetric supercapacitors

The supercapacitive performance of high-rate capacity and long-term cycling stability is still a big challenge for electroactive materials. Herein, Ni and Zn co-substituted Co carbonate hydroxide (NiZn-CoCH) flowers array is self-assembled on nickel foams (NFs) using l-ascorbic acid as a nanostructure inducer. The NiZn-CoCH flowers, consisting of silk-like nanosheets, are deservedly large electrode-electrolyte contact area and suitable ion-diffusion channel. The nanostructure and Ni and Zn co-substitution significantly improve energy storage performance. This electrode exhibits a high specific capacitance of 2020.8 F g^-1 at 1 A g^-1 with high-rate capacity (remain 80.2% at 10 A g^-1) and 5000-cycle stability (almost unchanged after 1500 cycles at 10 A g^-1). Additionally, an assembled asymmetric supercapacitor (ASC) device of NiZn-CoCH//activated carbon (AC) achieves a high energy density of 29.6 Wh kg^-1 at a power density of 375 W kg^-1 and only a 0.5% decrease of the capacitance after 2500 cycles. This facile and novel preparation method, using l-ascorbic acid, may be promising for industrial production of electroactive materials for the high-performance energy storage and conversion devices.