Facile Synthesis of NiCo 2 O 4 Nanowire Arrays/Few-Layered Ti 3 C 2 -MXene Composite as Binder-Free Electrode for High-Performance Supercapacitors.

Herein, a 3D hierarchical structure is constructed by growing NiCo2 O4 nanowires on few-layer Ti3 C2 nanosheets using Ni foam (NF) as substrate via simple vacuum filtration and solvothermal treatment. Ti3 C2 nanosheets are directly anchored on NF surface without binders or surfactants, and NiCo2 O4 nanowires composed of about 15 nm nanoparticles uniformly grow on Ti3 C2 /NF skeleton, which can provide abundant active sites and ion diffusion pathways for enhancing electrochemical performance. Benefiting from the unique structure feature and the synergistic effects of active materials, NiCo2 O4 /Ti3 C2 exhibits a high specific capacitance of 2468 F g-1 at a current density of 0.5 A g-1 and a good rate performance. Based on this, an asymmetric supercapacitor (ASC) based on NiCo2 O4 /Ti3 C2 as positive electrode and activated carbon (AC)/NF as negative electrode is assembled. The ASC achieves a high specific capacitance of 253 F g-1 at 1 A g-1 along with 91.5% retention over 10,000 cycles at 15 A g-1 . Furthermore, the ACS presents an outstanding energy density of 90 Wh kg-1 at the power density of 2880 W kg-1 . This work provides promising guidance for the fabrication of binder-free, free-standing and hierarchical composites for energy storage application.