Controllable synthesis of CoNb2O6 nanoparticles on multifunctional sulfur and phosphorus dual-doped graphene as advanced electrodes for hybrid supercapacitors

Battery type hybrid supercapacitors have drawn more attention as a great potential storage device with both excellent rate capability and high energy densities. Herein, we demonstrate a facile hydrothermal method to the preparation of sulfur and phosphorus atoms co-doping into the graphene nanosheet (SPG) using sulphuric acid and phytic acid as dopant. The NbCo precursor could be uniformly dispersed in SPG by formation of coordination bonds with the six phosphate groups of phytic acid. Morphological characteristic indicate that the CoNb2O6 nanoparticles grown directly on three-dimensional SPG framework (CoNb2O6/SPG) through high temperature calcination. As battery-type hybrid supercapacitors equipment, the asymmetric device consisting of CoNb2O6/SPG hybrids and active carbon (AC) delivers remarkable cycling stability (92.5% of the initial after 10,000 charge and discharge cycles) and outstanding rate capability (73.9% retention from 0.5 to 4 A g−1). More remarkably, the above device exhibits an impressive energy density of 39.7 Wh kg−1 at a high power density of 2995 Wkg-1. This outstanding performance is mainly ascribed to the large surface area and highly conductive of S and P co-doped 3D graphene architecture, the uniformly distributed and highly exposed CoNb2O6 nanoparticles and the incorporating effects with them.