Design and synthesis of 3D interconnected mesoporous NiCo2O4@CoxNi1−x(OH)2 core–shell nanosheet arrays with large areal capacitance and high rate performance for supercapacitors

Design and fabrication of high performance pseudocapacitors from 3D hierarchical hybrid electrodes with large areal capacitance and excellent rate capability still remains a challenge. Here, 3D hierarchical hybrid mesoporous NiCo2O4@CoxNi1−x(OH)2 core–shell nanosheet arrays on Ni foam have been rationally designed and facilely synthesized via an electrodeposited routine for pseudocapacitor applications. Electrochemical measurements show that the NiCo2O4@Co0.33Ni0.67(OH)2 electrode material exhibits a large areal capacitance as high as 5.71 F cm−2 at a current density of ∼5.5 mA cm−2, as a result of our high mass loading up to ∼5.5 mg cm−2. Moreover, it exhibits an excellent rate capability (∼83.7% capacitance retention at 273 mA cm−2). Based on these excellent properties, an asymmetric supercapacitor based on 3D hierarchical hybrid mesoporous NiCo2O4@Co0.33Ni0.67(OH)2 nanosheet arrays as the positive electrode and CMK-3 as the negative electrode was successfully fabricated. The as-fabricated device achieved the maximum areal capacitance of 887.5 mF cm−2 (specific capacitance of 87.9 F g−1) at 5 mA cm−2 with a stable operational voltage of 1.6 V and a high energy density of 31.2 W h kg−1 at a power density of 396 W kg−1. Moreover, two asymmetric supercapacitors in series could power 5 mm diameter red round light-emitting diode (LED) indicators efficiently for more than 5 minutes. The present 3D hierarchical hybrid material electrode with remarkable electrochemical properties has significant potential applications in high energy density storage systems.