In situ growth and anchoring NiCo2O4 nanowires on self-supported 3D holey graphene framework for supercapacitor

Developing high-energy supercapacitors (SCs) composed of nano-pseudocapacitive materials and highly conductive flexible three-dimensional (3D) holey carbon is a current research hotspot. However, the poor dispersion between the components of the system and the instability of the layered interface often results in low interface charge transfer capabilities and low performance. Herein, a 3D self-supporting flexible structure is engineered by tailoring graphene oxide quantum dot (GOQD)-induced in situ growth NiCo2O4 (NCO) nanowires anchored on the 3D holey graphene(3DHG) framework (3DHG/NCO) through a facile solvothermal reaction and subsequent annealing under Ar atmosphere. The method of GOQD-induced in situ growth not only effectively addresses the issue of dispersion of NCO nanowires, but also improves the structural stability and reduces the interface contact resistance because of the sufficient connections between NCO and the carbon frameworks, which can effectively eliminate the influence of volume changes and achieve large pseudocapacitance. Furthermore, 3DHG provides accessible active sites and longitudinal channels for the diffusion of ions/electrons, which greatly accelerates the formation of electrical double-layer capacitors (EDLCs). Therefore, the capacitance could be improved via the EDLCs mechanism in addition to the pseudocapacitive one. Based on such remarkable features, the obtained 3DHG/NCO electrode manifests a high specific capacitance (1118 F g-1 at 1 A g-1) and an excellent capacitance retention (95.04% after 5000 cycles). A fabricated 3DHG/NCO symmetric device displays a specific capacitance as 270 F g-1 at 1 A g-1, with an excellent energy density of 9.37 Wh kg-1 at 250 W kg-1. Moreover, the assembled SC maintains steady electrochemical performances under different tortuosity.