Biomass-derived activated carbon materials with plentiful heteroatoms for high-performance electrochemical capacitor electrodes

doi:10.1016/j.jechem.2015.11.008

Journal of Energy Chemistry

Volume 25, Issue 1, January 2016, Pages 35-40

https://doi.org/10.1016/j.jechem.2015.11.008 Get rights and content

Abstract

Activated carbons for electrochemical capacitor electrodes are prepared from soyabean using chemical activation with KOH. The pore size is easily controllable by changing the mass ratio between KOH and carbonized product. The as-prepared materials possess a large specific surface area, unique structure, well- developed hierarchical porosity and plentiful heteroatoms (mainly O and N). Thus resulted in its high specific capacitance, good rate capacity and cycling stability. Moreover, attributing to worldwide availability, renewable nature and low-cost, activated carbon prepared from soyabean has a good potential in energy conversion and storage devices.

Graphical abstract

Activated carbons possessing unique structure, well-developed hierarchical porosity and plentiful heteroatoms (mainly O and N) are prepared from soyabean using chemical activation with KOH and applied as electrode material for electrochemical capacitors.

Introduction

Electrochemical capacitor is a promising energy storage technology for applications where high power density and long-cycle life are required. Carbon materials have attracted intense interests as electrode materials for electrochemical capacitor, because of their high surface area, electrical conductivity, chemical stability and low cost [1]. Various carbonaceous materials, including carbon aerogels [2], [3], carbon nanotubes [4], [5], graphene [6], [7], ordered mesoporous carbons (OMCs) [8], [9] have been investigated as electrode materials of EDLC. However, the preparation for these carbons requires expensive and non-renewable raw materials, a lot of time and energy, and tedious preparation procedures [10]. By contrast, porous carbon materials derived from biomass are a potential choice for the construction of electrochemical capacitor electrodes owing to its worldwide availability, renewable nature and low-cost.

Up to now, many biomasses are converted into porous carbons, such as sunflower seed shell [10], broad beans [11], Rice husks [12] and collagen fiber [13], [14]. However, the porous carbon derived from biomass usually suffers from limited capacitance. Incorporating heteroatoms (mainly N and O) into the carbon framework is an efficient approach for enhancing the capacitance performance of carbons [15]. The incorporated heteroatoms not only enhance the surface wettability of carbon material which would increase the surface area accessible to aqueous electrolyte, but also provide extra pseudo-capacitance [16], [17], [18], [19]. In order to improve the charge storage ability, an efficient strategy is to carbonize heteroatom-containing precursors directly.

Herein, a heteroatom-enriched biomass, soyabean, has attracted our attention. Soyabean, as a renewable, abundant and environmentally friendly resource, is rich in carbon, nitrogen and oxygen elements, and thus can be carbonized into heteroatom-enriched carbon materials. We employ KOH as activated agent, and the pore structure can be easily tuned by changing the ration of KOH to carbon material. Symmetrical supercapacitors have been constructed and exhibited good electrochemical performance with a specific capacitance of 248.1 F/g at current density of 0.1 A/g and excellent cycle stability with 98.75% retention of the initial specific capacitance after 10,000 cycles at a current of 1 A/g.

Section snippets

Preparation of materials

Soyabean powders received from bean milk factory was put into a quartz boat in a tubular furnace and then heated to 400 °C and maintained for 2 h under N₂ atmosphere (at a ramp of 5 °C/min). The obtained black carbonized products were impregnated with KOH solution and then dried in an electric oven at 120 °C for 12 h. The dried mixture was activated in a muffle furnace under a flow of N₂ gas at 750 °C and maintained for 2 h (at a ramp of 5 °C/min). After cooling under nitrogen flow, the

Results and discussion

The as-prepared materials are first characterized by SEM. As shown in Fig. 1(a), the sample AC-2 shows plenty cavities on surface. Fig. 1(b) shows the morphology of AC-3. It was obvious that the hole size of AC-3 is bigger than that of AC-2, which might attribute to the higher mass ratio of KOH and carbonized product. As shown in Fig. 1(c), the sample AC-4 is composed of fewer holes but micrometric curves within the texture. The sufficient amount of KOH etch carbon atom to make the holes

Conclusions

A kind of porous carbon material containing plentiful heteroatoms (mainly O and N) have been successfully prepared using Soyabean as raw materials and applied as electrode material for electrochemical capacitors. The pore size of the porous carbon materials is tunable by adjusting the alkali/carbon ratio. The sample AC-4 possesses largest specific surface area of 2251 m²/g and the highest capacitance value of 248 F/g at 0.1 A/g. What's more, it has good rate capacity (56.7% capacity retention

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Citation Excerpt :
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Biomass-derived activated carbon materials with plentiful heteroatoms for high-performance electrochemical capacitor electrodes

Abstract

Graphical abstract

Introduction

Section snippets

Preparation of materials

Results and discussion

Conclusions

J. Power Sour.

Electrochima Acta

Electrochima Acta

Carbon

Bioresour. Technol.

Appl. Energy

Microporous Mesoporous Mater.

Electrochima Acta

J. Power Sour.

Nano Energy

Synth. Met.

Adv. Mater.

Nat. Mater.

J. Phys. Chem. Lett.

Nanoscale

Adv. Funct. Mater.