N-doped hollow mesoporous carbon spheres by improved dissolution-capture for supercapacitors

doi:10.1016/j.carbon.2019.09.091

Carbon

Volume 156, January 2020, Pages 523-528

https://doi.org/10.1016/j.carbon.2019.09.091 Get rights and content

Abstract

N-doped hollow mesoporous carbon sphere (N-HMCS) has attracted increasing attention as supercapacitor materials due to its rich mesoporous structure, large cavity, high surface area and suitable N-doping, etc. Herein, an improved dissolution-capture method is applied for preparation of N-HMCS using 3-aminophenol-formaldehyde (AF) resin spheres as carbon precursor. In this process, AF resin spheres preparation, mesoporous silica coating, dissolution-capture are implemented by one-pot process without multiple separation operation, which is beneficial for large-scale preparation. Mesoporous silica shell is in-situ coated on the surface of AF resin spheres, and AF oligomer, which is dissolved in N, N-dimethylformamide, is captured by mesopores on the silica shell. The obtained N-HMCS exhibits a relatively regular spherical shape, carbon shell with rich mesoporous, high surface area and nitrogen doping. As electrode materials in supercapacitor, the N-HMCS shows outstand performance with a high capacitance and a good capacitance retention, indicating its excellent promising in energy storage.

Graphical abstract

N-doped hollow carbon spheres with high performance in supercapacitor benefiting from its relative uniform and dispersed spherical morphology, carbon shell with rich mesoporous, high surface area and nitrogen doping are prepared by improved dissolution-capture using 3-aminophenol-formaldehyderesin spheres as carbon precursor avoiding resin sphere preparation and multiple separation operation.

Introduction

The gradual depletion of the accessible fuel-deposits caused by continuous increase in the consumption of fossil fuels has arouse widely attention [1]. It is of significance to develop high-efficient and economical energy storage systems as supplementary energy to fossil fuels [2]. As electrochemical energy storage devices, supercapacitors have been of great interest in a large number of applications, including hybrid electric vehicles, portable electronics, etc. [3] It is in critical need to develop advanced supercapacitor with high performance to keep up with the explosive market growth. The supercapacitor capacitance is directly dependent on the features of the electrode materials and exploiting nanostructured electrode materials with large surface area and high specific capacitance are essential.

Recently, as the electrode materials in supercapacitors, porous carbon materials have attracted much attention owing to high surface area, various shapes, morphology, pore size distributions and modifiable surface [4,5]. Especially, advanced hollow mesoporous carbon spheres (HMCS) have been widely explored as supercapacitor electrodes due to their excellent electrochemical performance, which is attributed to their nano-scaled shell thickness, rich mesoporous structure, large cavity and well-defined spherical structure [[6], [7], [8]].

There are many effective strategies for preparation of HMCS, including template methods or modified Stöber process, etc. In template methods, a sacrificial inner core is always required and mesopores are created on the carbon shell by addition of silica oligomers [9,10]. However, preparation and removal of template make operation complex and increase the cost. Modified Stöber process is also well accepted by synthetic chemists, by which inner cavities and porous structures are created and tuned by adjusting resin polymerization rate and silica source hydrolysis rate [[11], [12], [13]]. The Stöber process usually needs fewer steps compared with hard template method. However, the obtained HMCS through Stöber process shows low surface area and ununiform poor pore distribution. Although much progress has been made for preparation of HMCS, such as preparing HMCS by dissolving 3-aminophenol-formaldehyde resin (AF) [14] and silica additive [10], it is necessary to develop facile and efficient method for preparation of HMCS.

In our recent work, we have developed a dissolution-capture strategy to prepare HMCS. In that strategy, polystyrene spheres have been used as a core and carbon precursor to get carbon spheres by coating a mesoporous silica shell followed by dissolving, capturing, crosslinking and so on [15,16]. However, a pre-separation step is required, which makes operation complex. At the same time, low carbon residue, inert surface, and limited surface area and porosity restrict its performance promotion.

Resorcinol-Formaldehyde resin has been one of the common carbon sources for carbonaceous materials due to its easy preparation, low cost and relative high carbon residue [17]. Herein, an improved dissolution-capture strategy was developed to prepare nitrogen doping HMCS (N-HMCS) using AF resin sphere as carbon precursor. In this process, synthesis of AF resin spheres, coating silica, dissolution and capture are carried out in a one-pot process, avoiding pre-separation steps and improving the operational efficiency. The use of AF resin spheres not only leads to relative high carbon residue, but also achieves in-situ nitrogen doping. The excellent characteristics of spherical morphology, large cavity, high surface area, rich mesoporous structure and nitrogen doping are favorable for rapid diffusion of charge or ions, resulting in an obviously increased supercapacitor performance for N-HMCS.

Section snippets

Results and discussion

The N-HMCS is synthesized by an improved dissolution-capture method as illustrated in Scheme 1. Firstly, AF resin spheres are prepared through poly-condensation of 3-aminophenol and formaldehyde based on Stöber method. Then AF resin spheres are coated with mesoporous silica shell using hexadecyl trimethyl ammonium bromide (CTAB) as surface active agent and tetraethoxysilane (TEOS) as silica precursor to obtain AF@SiO₂. Subsequently, the AF resin spheres inside the silica shell are dissolved by

Conclusion

In summary, the N-HMCS with relative spherical morphology, large surface area, pore volume, rich mesoporous structure and nitrogen doping have been successfully synthesized through an improved dissolution-capture strategy. In this improved approach, batch addition in one-pot is adopted, which avoids the separation steps, greatly simplifies operation, and is beneficial to large-scale use. AF resin spheres act as carbon and nitrogen precursors to achieve nitrogen doping in carbon framework,

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work. They declare that they do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgements

We thank the Beijing National Laboratory for Molecular Sciences, Hebei One Hundred-Excellent Innovative Talent Program (III) (SLRC2017034), Hebei Province Introduction of Foreign Intelligence Projects (2018), National Natural Science Foundation of China (21676070).

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N-doped hollow mesoporous carbon spheres by improved dissolution-capture for supercapacitors

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusion

Declaration of competing interest

Acknowledgements

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