Remarkable supercapacitor performance of petal-like LDHs vertically grown on graphene/polypyrrole nanoflakes

A 3D hybrid nanostructure, in which petal-like ultrathin nickel-aluminum layered double hydroxides (LDHs) were vertically grown on a conductive graphene/polypyrrole (GP) substrate, was designed and fabricated by a facile hydrothermal method. SEM and TEM observations confirmed the successful synthesis of this specially designed nanostructure, in which the conductive substrate ensures very fast electron transfer during the charge-discharge process, whereas the 3D hierarchical structure facilitates rapid ion transfer. The ultrathin LDH nanoflakes (3-5 nm) expose their abundant active sites to the electrolyte, thus generating huge pseudocapacitance. Combining the abovementioned features, this specially designed 3D nanostructured hybrid possesses an exceptional specific capacitance (2395 F g(-1) at 1 A g(-1)), excellent rate performance (retaining 71.8% of capacitance at the current density of 20 A g(-1)), and remarkable cycling stability (99.6% retention after 10 000 cycles). Moreover, the assembled asymmetric supercapacitor obtained using GP@LDH as a positive electrode and GP-derived carbon as a negative electrode exhibits an ultrahigh energy density of 94.4 W h kg(-1) at the power density of 463.1 W kg(-1), making GP@LDH very attractive as an electrode material for high performance and low-cost supercapacitors.