MnO2 nanoflowers and polyaniline nanoribbons grown on hybrid graphene/Ni 3D scaffolds by in situ electrochemical techniques for high-performance asymmetric supercapacitors

It is highly desirable to develop asymmetric supercapacitors (ASCs) with high energy density while maintaining high power density and long cycle life. In view of this, various carbon and pseudocapacitor materials have often been introduced to form nanocomposite electrodes. But, until now, an energy density of ASCs over 40 W h kg(-1) at high power density has been a big issue. How to make the cathode and anode have high and comparable specific capacitance is crucial to obtain high energy density for practical application of ASCs. Herein, we report a hybrid 3D graphene/Ni foam (HGNF)-based MnO2/HGNF//polyaniline (PANI)/HGNF ASC, which was prepared by in situ electrochemical techniques. The cathode MnO2/HGNF and the anode PANI/HGNF provide high specific capacities of 480.0 and 478.8 F g(-1) at 1.0 A g(-1) respectively, which are highly comparable for ASCs. The MnO2/HGNF//PANI/HGNF ASC provides an excellent energy density of 41.0 W h kg(-1) at 787.3 W kg(-1). The reasons can be attributed to its 3D hybrid porous structure with fast electron and ion transfer rates and comparably high specific capacitances of both electrode materials, which can show both electrochemical double-layer capacitance and pseudocapacitance behaviors.