Solution blowing of ZnO nanoflake-encapsulated carbon nanofibers as electrodes for supercapacitors

Abstract

A facile spinning-based strategy is developed to fabricate zinc oxide nanoflake-encapsulated carbon nanofibers (ZnO/CNFs) as electrodes for supercapacitors. The zinc oxide/carbon nanofiber mats were solution blown with zinc acetate (Zn(Ac)₂) and polyacrylonitrile (PAN) as the metal and carbon precursor to get Zn(Ac)₂ core-enriched precursor nanofibers. After annealing under nitrogen, the precursor nanofibers were converted to ZnO/CNFs with ZnO nanoflakes encapsulated in the core of carbon nanofibers. In the constructed architecture, carbon nanofibers can avoid the direct exposure of ZnO to the electrolyte and preserve the structural and interfacial stabilization of ZnO nanoflakes. Meanwhile, the flexible entangled carbon nanofibers can accommodate temperate porosities thus providing the pore channel for electrolyte ions and maintain the structural and electrical integrity of the ZnO/CNF electrode during the charge–discharge processes. By loading different contents of ZnO, the microstructures of CNFs were changed, and the textural parameters significantly affected their electrochemical properties as electrodes. As a result, the ZnO/CNF electrodes exhibit high specific capacitance (216.3, 212.7, 208.8 and 172.5 F g⁻¹ at 1, 5, 10, and 50 A g⁻¹, respectively) and extremely excellent cycling performance at high current density (only 5.41% capacitance loss after 2000 cycles at a high rate of 10 A g⁻¹), with promising energy densities of 29.76 kW h kg⁻¹, over a power density range of 2.5–30 kW kg⁻¹. The ZnO/CNFs simultaneously exhibit excellent capacity retention. These encouraging results indicate great potential applications of ZnO/CNFs in developing energy storage devices with high energy and power densities.