Hollow N-doped carbon @ O-vacancies NiCo2O4 nanocages with a built-in electric field as high-performance cathodes for hybrid supercapacitor

Delicate design of nanostructured electrode materials with built-in electric field effect can make them have satisfactory electrochemical performance through the synergistic effects. Here, we prepare an advanced electrode material, a hollow N-doped carbon@O-vacancies NiCo2O4 nanocage (HNC@NiCo2O4), in which NiCo2O4 nanosheets are homogeneously grown on the N-doped carbon frame. This unique hollow nanocage can increase the contact-area between the material and electrolyte, further improving the electrochemical activities. Density functional theory simulations reveal that O-vacancies in NiCo2O4 can narrow the bandgap, which may contribute to the charge transfer dynamic of HNC@NiCo2O4 series. Meanwhile, N-doping can change the carbon-skeleton states density, thereby improving the electron-accepting capabilities for nearby NiCo2O4, and thus elevating the capacitive behaviors. Accordingly, a built-in electric field is in-situ constructed via the O-vacancies and N-doping. Due to the synergistic effect of a hollow structure and built-in electric field, as-fabricated HNC@NiCo2O4-0.45 electrode delivers noticeable specific-capacitance (966.2 F g(-1)@1 A g(-1)) and long-term endurance. Impressively, the HNC@NiCo2O4-0.45 electrode is employed to assemble a hybrid supercapacitor with the active carbon anode, which behaves a high energy-density (41.9 Wh kg(-1) at 750.4 W kg(-1)). Above results validate that the electric field modulation and nanostructure construction are important tactics to design a high-performance supercapacitor electrode. (C) 2020 Elsevier Ltd. All rights reserved.