Cerium-assembled tungsten oxide composite fibers: Adhesive-free electrodes for high performance asymmetric supercapacitors

In this study, in-situ cerium-assembled tungsten oxide carbon nanofibers were successfully prepared via simple electrospinning and calcination technology and were used as flexible electrodes without conductive agent and adhesive. It was confirmed that the introduction of Ce has better maintained the continuous morphology of onedimensional fibers to provide a continuous uninterrupted reaction position by the SEM TEM and XPS results. The addition of cerium improved the wettability of the material, which was propitious to the penetration of the electrolyte, made the electrolyte more fully contact with the active site, and enhanced the interface transmission effectiveness by the liquid contact angle test. Otherwise, the XRD and XPS results exhibited that the addition of cerium has caused the lattice expansion of the tungsten oxide, which generated the self-adjustable strain relaxation ability of electrode material in the process of continuous constant voltage charge and discharge. It proved that the introduction of cerium has promoted electron transfer, which improved the electrochemical performance of electrode material. In this paper, compared with WO3-CNFs without Ce, the Ce/WO3-CNFs have wide lattice spacing and hydrophilicity, fully contact with the electrolyte in the electrochemical reaction, and provide high electron transfer ability. The Ce/WO3-CNFs shows the maximum specific capacitance (407 F g-1) and excellent cycling stability (10,000 cycles at 5 A g-1 with a retention rate of 80 %). Otherwise, the flexible asymmetric supercapacitor device was prepared using the Ce/WO3-CNFs as cathode, and the CNFs as the anode, which exhibited the maximum energy density was 35.75 Wh kg-1 and a power density was 362.54 W kg-1 at 0.5A g-1. The results show that rare earth doping is an effective way and that the Ce/WO3-CNFs are promising electrode materials for supercapacitors.