Facile synthesis of cobalt-doped Ni₃(NO₃)₂(OH)₄ porous nanosheets for high-performance supercapacitors

As an emerging electrode material of supercapacitors, Ni₃(NO₃)₂(OH)₄ holds remarkable merits including environmental friendliness, large layer spacing (c = 6.9 Å), and high specific capacitance. Nevertheless, its rate capability and cycling stability have yet to be improved. Herein, a simple Co-doping strategy is introduced into the solution combustion preparation process to solve these problems. The optimized Co-doping dosage is determined to be 15 at.%, based on electrochemical performance test. The doped cobalt improves not only the rate capability by increasing electronic and ionic conductivity, but also the cycling stability by enhancing structural stabilization. Thanks to the benefits of Co-doping, the optimized sample simultaneously achieves high specific capacitance (1579 F/g at 1 A/g), excellent rate capability (78.3% capacity remains when current density increases from 1 to 20 A/g), and decent cycling stability (85.7% capacitance retention after 5000 cycles). At even an ultrahigh mass loading of 15.05 mg/cm², the specific capacitance remains still significant (1062 F/g at 1 A/g). When coupled with a commercial activated carbon electrode, the resulting asymmetric capacitor delivers a remarkable energy density of 26 Wh/Kg at a power density of 2766 W/Kg.