Abstract
Nitrogen-doped hollow carbon spheres (NHCSs) are well prepared by using Cu2O microspheres as a hard template and 3-aminophenol formaldehyde resin polymer as carbon and nitrogen precursors. The thickness of the carbon shell can be easily controlled in the range of 15–84 nm by simply adjusting the weight ratios of the precursors to Cu2O microspheres, and the Cu2O templates can also be further reused. Physicochemical characterization demonstrates that the obtained NHCSs possess a well-developed hollow spherical structure, thin carbon shell and high nitrogen doping content. Due to these characteristics, when further utilized as electrodes for supercapacitors, the NHCSs with the carbon shell thickness of 15 nm show a high capacitance of 263.6 F g−1 at 0.5 A g−1, an outstanding rate performance of 122 F g−1 at 20 A g−1 and an excellent long-term cycling stability with only 9.8% loss after 1000 cycles at 5 A g−1 in 6 M KOH aqueous electrolyte. This finding may push forward the development of carbon materials, exhibiting huge potential for electrochemical energy storage applications.
Highlights
A er self-polymerization of 3-aminophenol formaldehyde resin, followed by carbonization and etching template, all obtained Nitrogen-doped hollow carbon spheres (NHCSs) mainly inherit the spherical structure with smooth surfaces, and the diameters of the carbon spheres are almost unchanged compared with the Cu2O templates
When the amount of 3-aminophenol gradually increases, the thickness of NHCSs display monotonic increase with more 3-aminophenol and formaldehyde applied in the experiments, and the hollow structure of the NHCS with the larger thickness is more and more difficult to be destroyed during the etching template process. (Fig. S1, Electronic supplementary information (ESI)†)
According to the above results, we can conclude that the content of 3aminophenol and formaldehyde in synthesis system plays a key role on the morphology and the thickness of the NHCSs
Summary
NHCSs have been prepared by means of various synthetic approaches, including the Chemical Vapor Deposition (CVD), electric arc and template methods.[16,17,18,19,20,21,22] Among them, the template method has attracted people's attention due to its advantages such as simple operation and low cost. The hard template method is simple and effective way to prepare NHCSs. the templates currently used are mainly SiO2 nanoparticles and polymer latex particles,[26,27] these templates are non-recyclable, which increases the cost of hard template method to synthesize NHCSs in some certain cases. It is realized that the synthesis with an adjustable thickness of carbon shell can effectively improve the dielectric loss characteristics and increase matching characteristic impedance of NHCSs, resulting in enhancing electrochemical performances. We present a simple and effective strategy to synthesize NHCSs with the well-preserved spherical morphology, carbon shell thickness-controllable and high-nitrogen content via a hard template method (Scheme 1). The fabrication process uses 3aminophenol and formaldehyde polymer resins as carbon and nitrogen precursor, and Cu2O solid spheres as hard template. NHCSs with the thinnest carbon shell as supercapacitor electrodes exhibit a high speci c capacitance of 263.6 F gÀ1 at a current density of 0.5 A gÀ1, and long-cycling experiments present good cycle stability in 6 M KOH aqueous solution
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