Embedding partial sulfurization of iron-cobalt oxide nanoparticles into carbon nanofibers as an efficient electrode for the advanced asymmetric supercapacitor

In this paper, a series of partially sulfurized iron-cobalt oxide (FCOS) nanoparticles were embedded in carbon nanofibers (FCOS@CNF) via a simple electrospinning method and followed by a hydrothermal sulfurization process. The sulfurization degree of iron-cobalt oxide nanoparticles can be further controlled by tuning the hydrothermal reaction time. The self-supported FCOS@CNF samples with hierarchical nanostructure can not only effectively prevent the detaching of the FCOS nanoparticles but also provide abundant electrochemical active sites. When used as a supercapacitor electrode, the FCOS@CNF-10 electrode presents a high specific capacitance (1039 F.g(-1) at 1 A.g(-1)), a good rate performance (over 69.4% of capacitance retention from 1 to 15 A.g(-1)), and a long cycle lifespan (88.3% of capacitance retention after 4000 cycles at 10 A.g(-1)). A unique (FCOS@CNF-10//F-RGO) asymmetric supercapacitor device was assembled using the FCOS@CNF-10 sample as the positive electrode and the freeze-dried reductive graphene oxide (F-RGO) as the negative electrode. The hybrid device exhibits excellent electrochemical properties, including a high specific capacity, a long cycle life (86% after 5000 cycles at 10 A.g(-1)), and a maximum energy density of 24.2 Wh.kg(-1)@725.4 W.kg(-1).

Automated summary

In this study, partially sulfurized iron-cobalt oxide nanoparticles were embedded in carbon nanofibers via electrospinning and hydrothermal sulfurization. The resulting FCOS@CNF samples with hierarchical nanostructure exhibited high specific capacitance, good rate performance, and long cycle lifespan when used as supercapacitor electrodes.