•NiO@Co3O4 core/shell nanofibres were synthesized by a facile co-electrospinning method.•The electrochemical performances of NiO@Co3O4 core/shell nanofibres was superior to NiO and Co3O4 single nanofibres.•The advantage of core/shell fibre structures was discussed.NiO@Co3O4 core/shell nanofibres (NiO@Co3O4 NFs) as a promising supercapacitors electrode material were synthesized by a facile co-electrospinning method and heat treatment. The NiO core is about 125 nm in diameter and the Co3O4 shell has a thickness of ~80 nm. The electrochemical properties of NiO@Co3O4 NFs in 6 M KOH aqueous electrolyte are investigated. Compared with NiO (222 F g−1, 1 A g−1) and Co3O4 (284 F g−1, 1 A g−1) nanofibres, NiO@Co3O4 NFs electrode exhibits higher specific capacitance (437 F g−1, 1 A g−1), as well as good cycling stability (82.9% retention after 1000 cycles at 5 A g−1). The enhanced electrochemical performances can be attributed to the uniform core/shell fibre nanostructures. These results suggest that such NiO@Co3O4 NFs would be promising electrodes for supercapacitors.

Undoped TiO2 nanoparticles are synthesized by the sol–gel method. X-ray diffraction (XRD) analysis reveals that the samples have the pure anatase TiO2 structure and the crystallinity becomes better with increase of the annealed temperature. Scanning electron microscopy (SEM) observation shows that the resulted particles are uniformly shaped like spheres. The vibrating sample magnetometer (VSM) measurement shows that the TiO2 nanoparticles exhibit weak ferromagnetism, and the saturation magnetization is increased with increasing the annealed temperature. X-ray photoelectron spectra (XPS) analyses confirm that the binding energy of Ti 2p peaks shifts to higher energy and the oxygen vacancies are formed in the as-prepared samples. Based on the above investigation, the origin of the ferromagnetism in the TiO2 nanoparticles is attributed to the 3d orbits of a small amount of tetravalent titanium cations which are occupied by electrons, then tetravalent titanium cations convert into trivalent or divalent titanium cations, indicating that the ferromagnetism of the samples is due to charge transfer interactions between Ti3+ and Ti2+ cations.

The as-obtained nickel doped DLC films by the electrochemical process demonstrated the surface morphology of a nano-tip transformed to bumps with increasing nickel compound concentration in the electrolyte, simultaneously the sp2-C content greatly increased. Nickel was incorporated into highly cross-linked amorphous carbon matrix, forming the typical nanocrystalline/amorphous composite microstructure, which was in the form of element nickel, nickel hydroxide, and nickel oxide. Field emission performance showed that nickel incorporation effectively lowers the threshold field from 9.9 to 8.4 V/μm at the electron emission current density of 1 μA/cm2, and greatly increased the emission current density from 21.88 to 163.89 μA/cm2 under 12.455 V/μm for DLC film. The Raman and XPS measurements of the as-deposited films suggested that spatially localized conduction channels formed by the graphite-like sp2-carbon and metallic particles might be responsible for the electron emission in nickel-doped DLC films.Graphical abstractThe nickel-doped DLC films with the nickel concentration of 5 mg/L had excellent field emission performance, and it corresponded with the F–N theory.Highlights► Nickel incorporated diamond-like carbon nanocomposite films were fabricated. ► The typical nanocrystalline/amorphous composite structure for samples. ► Excellent field emission performance of Ni/DLC films with the nickel concentration of 5 mg/L. ► The relationship between the microstructure and field emission performance was discussed.