Oxygen-vacancy Bi2O3 nanosheet arrays with excellent rate capability and CoNi2S4 nanoparticles immobilized on N-doped graphene nanotubes as robust electrode materials for high-energy asymmetric supercapacitors

In this paper, we constructed oxygen vacancy-containing Bi2O3 nanosheet arrays (OV-Bi2O3 NSAs) with typical mesoporous structures and CoNi2S4 nanoparticles (CoNi2S4 NPs) grown on N-doped graphene nanotubes (N-GNTs) through facile approaches. The as-fabricated OV-Bi2O3 NSAs and CoNi2S4 NPs were specifically used as advanced freestanding negative and positive electrodes, respectively, for application in asymmetric supercapacitors (ASCs). The introduction of ample vacancies to Bi2O3 NSAs can not only enhance their electronic conductivity and donor density but also ameliorate their surface features, which greatly enables the transport of electrolyte ions and electrons, giving rise to rapid redox processes at the Bi2O3/electrolyte interfaces. Benefiting from the introduction of the oxygen vacancies and the particular morphologies, as well as the synergistic contributions of various components in the nanohybrid electrode, the N-GNTs@OV-Bi2O3 NSA electrode delivers a substantially appreciable specific capacitance of 643 F g(-1) at 1 A g(-1) coupled with exceptional rate capability. Moreover, the as-synthesized N-GNTs@CoNi2S4 NP electrode also presents an ultrahigh specific capacitance of 2142 F g(-1) at 2.5 A g(-1). More importantly, the assembled N-GNTs@OV-Bi2O3 NSAs//N-GNTs@CoNi2S4 NP asymmetric supercapacitor with an expanded operation voltage of 1.6 V yields a maximum specific energy density of 86.6 W h kg(-1) at a power density of 1.6 kW kg(-1) and outstanding cycling characteristics (85% capacitance retention after 10000 cycles). This study underscores the potential significance of both incorporating oxygen vacancies into metal compounds and integrating the conductive skeleton with the active materials as a strategy for augmenting the electrochemical performances of the electrode materials.