δ-MnO2/holey graphene hybrid fiber for all-solid-state supercapacitor

Abstract

δ-MnO₂/holey reduced graphene oxide (HRGO) fiber electrodes with good flexibility and enhanced electrochemical performance were prepared by depositing δ-MnO₂ on the surface of the holey reduced graphene oxide fibers. HRGO-650 was obtained by soaking graphene oxide in a 0.5 M H₃PO₄ solution for 12 h followed by calcining it at 650 °C for 2 h in N₂. The loose curling manganese oxide nanosheets are reassembled on the surface of the HRGO-650 fiber freely, causing the close contact between the manganese oxide nanosheets and the graphene nanosheets. The prepared δ-MnO_2(4.0)/HRGO fiber electrode shows a larger specific capacitance (245 F g⁻¹) at a current density of 1 A g⁻¹ in the 1 M Na₂SO₄ electrolyte. An all-solid-state fiber supercapacitor was assembled by two intertwined δ-MnO_2(4.0)/HRGO fiber electrodes, both of which are solidified in a H₃PO₄–polyvinyl alcohol (PVA) gel electrolyte. This all-solid-state δ-MnO_2(4.0)/HRGO fiber supercapacitor not only shows good flexibility, but also gives enhanced capacitive performance. The optimal all-solid-state δ-MnO_2(4.0)/HRGO fiber supercapacitor obtains a high area-specific capacitance (16.3–16.7 mF cm⁻²) at a current density of 0.05 mA cm⁻², enhanced rate capability (64% capacitance retention from 0.05–0.6 mA cm⁻²), and relative good stability (80% of initial capacitance values after 1000 cycles). This method is expected to improve the conductivity and capacitance for all-solid-state carbon-based fiber supercapacitor with good flexibility and light weight.