Received: 15 Mar 2018
Accepted: 25 Mar 2018
Published online: 26 Mar 2018

Biomass-derived nitrogen-doped porous carbons (NPC) and NPC/polyaniline composites as high performance supercapacitor materials

Xizhi Wang, Xiaofei Zeng and Dapeng Cao*

State Key Laboratory of Organic-Inorganic Composites, and Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China

* Corresponding Author(E-mail) :


Currently, developing high performance supercapacitor material suitable for application in the areas which require high energy density battery, is still a great challenge. Here we use biomass poplar sawdust as precursors to prepare nitrogen-doped porous carbons (NPC) and the NPC/polyaniline (PANI) composites, and further explore its application in supercapacitor electrodes. By optimizing the carbonization temperature, we find the NPC-750 sample shows a highest specific capacitance of 362 F∙g-1 in 6 M KOH at 0.5 A∙g-1 among the four samples, due to its large specific surface area of 2149 m2·g-1, and suitable pore size distribution and high graphitization degree. Further investigations indicate that NPC/PANI composite exhibits a much higher specific capacitance of 312 F∙g-1 than 252 F∙g-1 of NPC at 5 A∙g-1, and a wider voltage range of 0-1.4 V than the one of 0-1V of NPC, as well as a much higher energy density of 15.45 Wh∙kg−1, which is 2.73 times of 5.66 Wh∙kg−1 of NPC. This work indicates that integrating porous carbon and PANI into a composite is a promising strategy for developing high performance supercapacitor electrode materials.

Table of Contents

The biomass poplar sawdust is used as precursors to prepare nitrogen-doped porous carbons (NPC) and the NPC/polyaniline (PANI) composites, and further explore its application in supercapacitor electrodes.



Keywords: Nitrogen-doped porous carbons; Energy storage and conversion; Biomass waste reutilization; Polymer composites

1. Introduction

With the fast consumption of traditional fossil fuels (e.g. coal and oil and nature gas) and the growing energy requirement of the current society, it is an urgent task to develop high efficient, inexpensive and environmentally friendly conversion technologies and energy storage systems.1, 2 Recently, development of energy storage devices such as batteries and supercapacitors has received more and more attention. Compared with traditional batteries, supercapacitor is a new type of electrochemical energy storage cell with high power density and excellent cycling stability. It can be charged–discharged in a matter of seconds and almost no pollution to the environment, and is very suitable for applying in the areas which require high power density batteries.3-8 Therefore, developing high performance supercapacitor materials is a current hot topic.

According to the different charge-storage mechanism, supercapacitors can be categorized into two categories: electrical double-layer capacitors (EDLCs) and Faradaic capacitors.9 Faradaic capacitors are primarily dominated by reversible redox reactions at the surface of the electrode materials,10 and the frequently used electrode materials contain metal oxides11, functionalized carbon powders12 and conducting polymers,13 while EDLCs store energy by accumulating electrostatic charge in the electric double layers at the electrode/electrolyte interface, and no electrochemical reaction occurs in the process.14 Activated carbon,15 carbon nanotube,16 carbon aerogels,17 graphene18,19 and carbide-derived carbons,20 have been widely considered as EDLCs electrode materials, owing to their chemical and thermal stability, high specific surface area, desirable electric conductivity and relatively low cost.5,18,21 Recently, the composite materials combining the EDLCs and Faradaic capacitance have been proposed to accomplish the performance beyond the limitations of each material,22 such as carbon/conducting polymer composites23,24 and carbon/metal oxide composites.25, 26

Currently, using metal-organic framework (MOF),18,21 biomass27-29 and other hard template30 as precursors to obtain porous carbons has been reported extensively.31,32 Compared to MOF and hard templates, biomass precursors show a lot of advantages, such as low cost, specific texture structure by natural selection and easy accessibility.29 Moreover, using biomass as precursors to obtain porous carbon can achieve reutilization of waste biomass and avoid traditional plant waste burning which often causes severe environmental pollutions and even leads to the fog and haze weather. Therefore, it is significantly important to use waste biomass as precursors to synthesize the porous carbons for supercapacitor application.

Previous investigations have reported a series of biomass-derived porous carbons and their applications in supercapacitors. Willow catkins,29 waste celtuce leaves,33 chicken eggshell membranes,34 eggplants35 and natural crab shell36 as highly accessible waste biomass sources, have been used to prepare the corresponding activated carbons by KOH activation process, and these as-synthesized samples show the capacitance of about 300 F/g in alkaline electrolytes.37 These investigations indicate that KOH is a good activating reagent,38-40 and the proper precursor, activation agent and preparation method would synergistically affect the electrochemical properties of the synthesized porous carbons.9  Although activated carbon is the most widely used materials for supercapacitor due to its high specific surface area, excellent chemical stability and high conductivity,41 most activated carbon suffers from poor rate performance because of the insufficient ion diffusion within the micropores, which limits their energy density (5–8 Whkg−1) and power density.42

Polyaniline (PANI) was considered as one of the most attractive materials due to its easy synthesis, low cost and high electrical conductivity.43,44 Recently, PANI has been widely used to prepare carbon/PANI composites for improving supercapacitor performance, especially the power and energy densities.35,45,46 Gupta et al. prepared a PANI/SWCNT composite with a specific capacitance of 463 F∙g-1.47 Li et al. reported a carbon/PANI composite with specific capacitance of 747 F∙g-1 at a current density of 0.1 A∙g-1.48 Uppugalla et al. also found that heteroatom-doped carbon (CNSO)/PANI composite yielded a higher capacitance of 372 F∙g-1 than CNSO.49 Moreover, Yu et al reported that HPC/PANI nanowire composite exhibits a voltage window of 0–1.8 V, a high energy density of 60.3 Whkg-1 and power density of 18 kWkg-1 in 1 M Na2SO4.41 All above these studies indicate that the synergistic effects between carbon materials and PANI could enhance the specific capacitance of carbon materials significantly.

In this work, we first synthesize nitrogen-doped porous carbons (NPC) by using biomass poplar sawdust as precursors. By exploring the effects of temperature on the as-synthesized samples, we screen an optimal carbon sample NPC-750 to further prepare the NPC/PANI composites by in situ polymerization of aniline on it. Then, the voltage range and energy density of the NPC/PANI composites were studied. Finally, conclusions were drawn and the discussion was addressed.  

2. Results and Discussion

Scheme 1 Schematic illustration of the preparation of poplar sawdust-derived nitrogen-doped porous carbons (NPC) and NPC/PANI Composites

Scheme 1 shows the illustration of preparation of NPC and NPC/PANI composites. First, the raw sawdust was washed by 1 M HCl and water and then dried in an oven. The dried sample was grinded into powder and mixed with KOH powder in solid phase for further carbonization at different temperatures (T=650, 700, 750, 800°C) for 3 h in argon atmosphere. The obtained carbon materials were marked as NPC-X, where X indicates the activation temperature. Subsequently, the prepared carbons were washed by 1 M HCl and water and dried in an oven. The selected NPC was further used to prepare the NPC/PANI composites by in situ polymerization of aniline monomer on NPC material. The detailed synthesis and characterization were presented in Supporting Information.