High-performance all-solid-state hybrid supercapacitors based on surface-embedded bimetallic oxide nanograins loaded onto carbon nanofiber and activated carbon

By exploiting the facile advantages of the electrospinning process, we decorated NiCo-based bimetallic oxide nanoparticles with a tunable stoichiometric ratio onto carbon nanofibers (CNFs) and subsequently heat-treated them as an electrode assembly. The bimetallic loading density on the fibrous network was similar to 32 wt%, and the Ni:Co stoichiometric ratio was varied; the high-Ni-loaded (Ni-40:Co-20) nanofibrous electrode showed a specific capacity of 80.2C g(-1) at a current density of 1 A g(-1), and the specific capacity increased to 165.6C g(-1) when the Co loading was increased to Ni-20:Co-40. CNFs embedded with NiCo bimetallic oxide-based electrode showed 84.3% capacity retention even after cycling at 10 A g(-1). The Co-rich electrode assemblies presented excellent cyclic stability of 94.9% capacity retention after 3000 cycles at 5 A g(-1) and excellent rate capability and low internal charge resistance. The all-solid-state asymmetric supercapacitor of the C-NiCoO NFs//activated carbon device exhibited a cell specific capacitance of 191.4 F g(-1) at a current density of 1 A g(-1) in the potential window from 0 to 1.6 V and exhibited a maximum energy density of 67.9 W h kg(-1). Surface-embedded NixCoyO4 nanoparticles on CNFs exhibited superior electrochemical properties because of the uniform monodispersive nanograin network over the carbon fibrous conductive surface and the effective reversible redox reaction ability of the bimetallic sites. The thin-layered graphite features of the bimetallic nanograins improved their electrical conductivity and prevented aggregation of the nanoparticles, thereby promoting cyclic stability and avoiding leaching from the carbon fibrous surface. (C) 2019 Elsevier Ltd. All rights reserved.