Interface Engineering Based on Multinanoscale Heterojunctions between NiO Quantum Dots, N-Doped Amorphous Carbon and Ni for Advanced Supercapacitor

Energy storage ability is determined by the ion arrangement and electron transfer at the electrode–electrolyte interface, which depends on combining materials that form complex heterogeneous interfaces. Herein, we developed a nitrogen-doped (N-doped) in situ carbon-coated NiO quantum dots/Ni (∼5 nm) with multilevel heterogeneous interface as supercapacitor electrode materials by a simple method based on coordination reaction. The coated quantum dots heterojuction interfaces between NiO and Ni optimizing the electronic structures and provide a large specific surface area of 263 m2/g. This complex heterogeneous interfaces is effectively increasing the structural stability during electrochemical reactions while improving the conductivity. The N-doped carbon shell with a large surface area increases the contact site and wettability between electrode material and electrolyte, which reduces concentration polarization then improves the ionic conductivity. In addition, a synergistic effect of carbon shell and NiO quantum dots resulted in effective capacitance enhancement of composites with less redox active substances. Carbon nanotubes (CNT) were used as an electronic transmission bridge between active materials and current collector by physical mixing with electrode materials. The NiO QDs/Ni@NC-4-CNT electrode exhibited a specific capacitance of 660.1 F/g at 0.5 A/g. Assembled NiO QDs/Ni@NC-4-CNT//AC supercapacitor device exhibits a specific capacitance of 223.2 F/g at a large current density of 20 A/g. While after 5000 charge/discharge cycles at 5 A/g, a specific capacitance of up to 149.2 F/g is maintained, demonstrating that the proposed material has excellent performance for supercapacitor application.