Nitrogen-doped carbon dots anchored NiO/Co3O4 ultrathin nanosheets as advanced cathodes for hybrid supercapacitors
Graphical abstract
Introduction
With the gradual consumption of fossil fuel, the development of energy storage devices has become global concerns [1], [2]. As one of the prime choices, supercapacitors have elicited a great scientific interest by virtue of their desirable power density and fast charge–discharge rate [3], [4], [5]. Whereas, the poor energy density of supercapacitors severely hinder their use in energy storage systems [6], [7], [8]. Accordingly, numerous efforts have been dedicated to improve the energy density of supercapacitors without decreasing the power density of them. More recently, hybrid supercapacitors consisting of a capacitive electrode and a battery-like electrode are able to deliver much higher energy density than conventional supercapacitors due to the larger specific capacities of the battery-type materials [9], [10], [11]. Transition metal oxides are demonstrated to be superior battery-type electrode materials on account of their naturtal abundance and environmental friendliness [12]. Among these materials, NiO with ultrahigh theoretical capacity and Co3O4 with long cycling life have elicited the extensive interest as redox-active electrodes for supercapacitors [13], [14], [15]. Compared with the corresponding individual constituents, the effective combination of NiO and Co3O4 could offer competitive advantages for the increment of electrochemical activity [16]. However, the major obstacles for NiO/Co3O4 composites are their low specific surface area and poor electrical conductivity owing to their semiconductor nature. These disadvantages would lead to a lower specific capacity of NiO/Co3O4 composites and severely confine their further development in supercapacitors.
In order to overcome the above obstacles, integrating conductive carbon and constructing nanostructured materials are considered as plausible methods to optimize the electrochemical properties of NiO/Co3O4 [1], [17]. Recently, carbon dots, as a new type of zero-dimensional carbonaceous materials, have become the focus in the field of basic research owing to their diverse physicochemical properties and beneficial attributes, such as low production cost, good dispersion in solvent, and excellent surface grafting ability [18], [19]. It is found that carbon dots can provide a favorable interface for the interaction between electrolyte and electrodes, thus improving the specific capacities and cycle stabilities of the electrode materials. The emergence of carbon dots have exhibit exciting prospects in the energy conversion and storage fields [20]. On the other hand, attributing to the higher specific surface area, more exposed active sites and larger degree of anisotropy, ultrathin two-dimensional nanostructures offer superior charge storage characteristics for the electrode materials and have attracted increasing interest in electrochemical energy storage systems [21], [22]. Unfortunately, few study has been reported on carbon dots anchored NiO/Co3O4 two-dimensional nanostructures for energy storage applications. Herein, we developed an advanced cathode of ultrathin NiO/Co3O4 nanosheets supported nitrogen-doped carbon dots (NCDs) for hybrid supercapacitors. The NiO/Co3O4/NCDs ultrathin nanosheets were successfully synthetized through a hydrothermal-calcination two-step strategy, which realize simultaneous boosts in specific capacity (976.3 C g−1, 1 A g−1) and cycle stability (95.7% retention, 10,000 cycles). Meanwhile, a corresponding hybrid supercapacitor device based on NiO/Co3O4/NCDs ultrathin nanosheets and reduced graphene oxide (RGO)/NCDs shows a high energy density of 41.6 Wh kg−1 at 800 W kg−1 with excellent cycling stability (no decay after 10,000 cycles at 10 A g−1), suggesting the high application potential of NiO/Co3O4/NCDs ultrathin nanosheets for energy storage systems.
Section snippets
Synthesis of NiO/NCDs and Co3O4/NCDs composites
The chemicals were of analytical level and used without further purification. The NCDs were fabricated by a hydrothermal method according to our previous work [23]. For the preparation of NiO/NCDs composites, NCDs powder and Ni(Ac)2·4H2O (0.5 g) were dissolved in 35 mL of deionized water. The mixed solution was stirred for 30 min and then transferred to a 50 mL polytetrafluoroethylene (PTFE) autoclave. After reaction at 180 °C for 10 h, the precursor was washed with deionized water and ethanol,
Results and discussion
The crystal structures of NiO/NCDs-2 and NiO/Co3O4/NCDs composites were firstly characterized by XRD (Fig. 1). The diffraction pattern of NiO/NCDs-2 composites corresponds to the cubic structure of NiO (JCPDS 65–5745). Because of the poor crystallinity and low amount of NCDs, the characteristic peaks of NCDs can not be found in NiO/NCDs-2 [25]. With the increase of cobalt salt content, new characteristic diffraction peaks corresponding to cubic Co3O4 (JCPDS 42–1467) become more pronounced.
Conclusion
To sum up, the NiO/Co3O4/NCDs ternary composites have been successfully prepared by an effective hydrothermal-calcination two-step strategy. An ultrathin graphene-like porous architecture can be generated after combination Co3O4 with NiO/NCDs composites. Benefitting from the particular structure and ternary composition, the NiO/Co3O4/NCDs composites possess an enhanced specific capacity (976.3 C g−1 at 1 A g−1) and a splendid cycling stability (4.3% loss after 10,000 cycles). The hybrid
CRediT authorship contribution statement
Zhenyuan Ji: Writing - original draft, Methodology, Conceptualization. Kai Liu: Investigation, Validation. Na Li: Methodology, Validation. Hongyan Zhang: Validation. Wenyao Dai: Investigation, Software. Xiaoping Shen: Writing - review & editing, Methodology. Guoxing Zhu: Writing - review & editing. Lirong Kong: Formal analysis, Software. Aihua Yuan: Formal analysis, Resources.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Financial support from the National Natural Science Foundation of China (51602129 and 21875091) and the Young Talents Training Program of Jiangsu University.
References (53)
- et al.
Nano Energy
(2018) - et al.
Energy Storage Mater.
(2017) - et al.
J. Power Sources
(2013) - et al.
Energy Storage Mater.
(2019) - et al.
Electrochim. Acta
(2013) - et al.
Mater. Today
(2019) - et al.
Appl. Catal. B
(2018) - et al.
Adv. Colloid Interface Sci.
(2018) - et al.
J. Colloid Interface Sci.
(2019) - et al.
Electrochim. Acta
(2020)
Chem. Phys. Lett.
Electrochim. Acta
Sol. Energy Mat. Sol. C
Appl. Surf. Sci.
Carbon
Chem. Eng. J.
Energy Storage Mater.
J. Alloys Compd.
Electrochim. Acta
Chem. Eng. J.
J. Alloys Compd.
Chem. Eng. J.
Chem. Eng. J.
Electrochim. Acta
Chem. Eng. J.
Adv. Sci.
Cited by (43)
Recent advances of carbon dots based emerging materials for supercapacitors applications
2024, Journal of Energy StorageAssembly of high-performance nickel–cobalt supercapacitors modified with heteroatomic polymer carbon
2024, Applied Surface ScienceCo-doped SnS microsphere decorated carbon nanofiber flexible films for supercapacitor applications
2023, Journal of Alloys and Compounds