Elsevier

Materials Letters

Volume 174, 1 July 2016, Pages 249-252
Materials Letters

Bio-inspired hollow activated carbon microtubes derived from willow catkins for supercapacitors with high volumetric performance

https://doi.org/10.1016/j.matlet.2016.03.063Get rights and content

Highlights

  • Hollow activated carbon microtubes (HACMs) are prepared from willow catkins for the first time.

  • The HACMs show high surface area of 1107 m2 g−1 and concentrated pore size distribution.

  • The HACMs electrode exhibits high gravimetric capacitance of 306 F g−1 and outstanding volumetric capacitance of 303 F cm−3.

Abstract

A novel bio-inspired hollow activated carbon microtubes (HACMs) was prepared from low-cost, renewable biomass willow catkins by low temperature pre-carbonization combined with KOH chemical activation and used as supercapacitor electrode materials. The as-prepared HACMs exhibit hollow fiber-like structure with thin wall thickness of less than 1 µm, high microporosity surface area (997 m2 g−1) and concentrated pore size distribution (1–2 nm). The electrochemical measurement results demonstrate that the HACMs electrode materials have high gravimetric capacitance of 306 F g−1 superior to most of the previously reported activated carbons and outstanding volumetric capacitance of 303 F cm−3.

Introduction

Considering the ever-growing demands in energy storage systems, miniaturized portable electric devices with high volumetric performances, it is urgently needed to minimize the volume of devices [1], [2]. Among energy storage systems, supercapacitors have attracted considerable attention due to their fast charge-discharge characteristics, high power density and long cycling stability. Activated carbons (ACs) are widely used as electrode materials for supercapacitors based on their high specific surface area (SSA), low-cost and environmental compatibility. Generally, ACs with well-developed porosity and high SSA often lead to high gravimetric capacitance. However, the volumetric capacitance of ACs is rather low due to the high porosity [3].

Activated carbon fibers (ACFs) have many advantages over the ACs such as micropores-dominated characteristic and micropores open directly to the exterior. Among the ACFs, a kind of specific carbon fibers with hollow structure has attracted researchers' attention greatly [4]. Due to the unique structure, hollow activated carbon fibers (HACFs) possess larger surface area and higher ion adsorption-desorption rate, which is more preferable for energy storage application. Herein, we used willow catkins as precursor to prepare HACMs. The as-synthesized HACMs possessed hollow fiber-like structure, high microporosity surface area, concentrated pore size distribution (PSD) but low porosity that results in high volumetric capacitance. The HACMs were proved to be a promising candidate for supercapacitors electrode materials.

Section snippets

Preparation of HACMs

In a typical process, a certain amounts of feed willow catkins (WCs) was washed with deionized water repeatedly to remove adherent soil and impurities, dried at 100 °C overnight. Then, the WCs was pre-carbonized at 500 °C for 2 h, fully mixed with KOH at the mass ratio of 1:1 and followed by evaporating water at 80 °C. The mixture was pyrolyzed in a nickel crucible at 700 °C for 1 h under nitrogen flow. After being cooled to room temperature, the annealed samples were washed with 1 M HCl and deionized

Results and discussion

Fig. 1a and b shows the SEM images of the carbonized WCs, the samples are exhibited long hollow tubular-like structure with coarse surface and covered by large amounts of spherical granules. The wall thicknesses are less than 1 µm while the outer diameters are less than 10 µm. The morphology of the samples was derivative from the pristine biomass (inset in Fig. 1a and Fig. S1). Fig. 1c and d show that the HACMs still retain original hollow configuration while small amounts of the samples collapse

Conclusions

In summary, bio-inspired HACMs has been fabricated by pre-carbonization and KOH activation of biomass willow catkins. The obtained HACMs exhibit hollow fiber-like structure with thin wall thickness, resulting in high microporosity surface area (997 m2 g−1) and concentrated PSD (1–2 nm) but low pore volume. HACMs are proved to be a promising candidate for supercapacitors with high gravimetric capacitance of 306 F g−1 and superb volumetric capacitance of 303 F cm−3.

Acknowledgments

This work was financially supported by the Natural Science Foundation of Shanxi Province (No. 2012011219-3).

References (8)

  • C. Long et al.

    Carbon

    (2015)
  • X. Du et al.

    Bioresour. Technol.

    (2013)
  • K. Wang et al.

    Electrochim. Acta

    (2015)
  • M. Sevilla et al.

    Energy Environ. Sci.

    (2014)
There are more references available in the full text version of this article.

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