MOFs-derived niobium oxide nanoparticles/carbon nanofiber hybrid paper as flexible binder-free electrode for solid-state asymmetric supercapacitors

Abstract

For the first time, a bottom-up approach was adopted to prepare free-standing orthorhombic Nb2O5-anchored carbon nanofibers (Nb2O5 @CNFs) hybrid paper via in-situ solvothermal synthesis of Nb-metal organic framework@CNFs hybrid and subsequent pyrolysis process. The nanocrystalline Nb2O5 decorated on the CNF surfaces improved the charge storage performance through synergistic effect between porous CNFs (EDLC) and Nb2O5 (pseudocapacitance). Moreover, the high surface area and core-shell structure of Nb2O5 @CNF hybrid reduce diffusion limitations and facilitate ionic transport. The Nb2O5 @CNF hybrid paper as a binder-free electrode delivered greater specific capacitance of 633.6 F/g (975.7 F/cm3) in 1 M H2SO4, compared to Li2SO4 electrolyte (524.3 F/g) at 0.5 A/g. However, the Nb2O5 @CNF electrode showed better cycling stability in neutral Li2SO4 electrolyte than in acidic H2SO4 electrolyte. The solid-state asymmetric supercapacitor (ASC) based on Nb2O5 @CNF paper and activated carbon (AC) electrodes delivered higher energy density of 62.1 Wh kg−1 at 292.7 W kg−1 in Li2SO4 electrolyte due to a wider working potential window (0–1.5 V), compared to H2SO4 electrolyte (55 Wh kg−1). The Li2SO4-based ASC cell is also capable of producing an energy density of up to 45.6 Wh kg−1, even at a high-power density of up to 5853.6 W kg−1. The as-assembled ASC demonstrated low self-discharge rate as well as excellent bending stability, indicating its excellent prospects in real-life applications.