Facile synthesis of 3D hierarchical N-doped graphene nanosheet/cobalt encapsulated carbon nanotubes for high energy density asymmetric supercapacitors

The 3D NG/Co–NCNT based asymmetric supercapacitors provide high energy density (~88.44 W h kg −1 ), an ultra-high power density (~17 991 W kg −1 at 56.97 W h kg −1 ), and outstanding stability (~10 000 times).