A team of researchers from Canada and China recently developed a new method to utilize doped carbon obtained from bamboo in silicon carbide and nitrogen-based supercapacitors. This research is published in Chemical Engineering Journal.
Study: Bamboo-derived carbon material inherently doped with SiC and nitrogen for flexible supercapacitors. Image Credit: OHishiapply/Shutterstock.com
Carbon as the Pivot Material in the Electrodes of Supercapacitors
Among various energy storage systems, supercapacitors are promising candidates as energy storage devices, owing to excellent charge/discharge capability, high-power density, and exceptional stability.
Carbon materials are highly available and cost-effective electrode materials, especially for electrochemical double-layer capacitors (EDLCs) because of their high surface, efficient charge storage capability, favorable pore-size distribution with hierarchical architecture for rapid ion transport, relatively moderate electrical conductivity, and chemical and thermal stability.
They provide an excellent platform for inducing heteroatoms or functional groups and defects to enhance the active sites for efficient charge storage and effective modulation of their electronic and chemical characteristics.
Bamboo: A Natural Source of Carbon materials
As environmental concerns are growing, bio-renewable carbon materials along with non-complex synthetic routes are highly sought. The natural bamboo has garnered substantial focus due to highly interconnected ionic channels, inherent silicon dioxide contents, and nitrogen-containing functional groups with a constant chemical composition consisting of lignin, cellulose, and hemicellulose, and others. Naturally, it contains self-doped hierarchically porous carbon materials.
Also, it has rich silicon dioxide contents which act as a natural host for the successful doping of silicon carbide species as well as for creating a porous architecture and suitable morphology along with inherent nitrogen-containing functional groups.
Silicon Carbide: Advantages and Limitations in Electrodes Materials
Silicon carbide (SiC) is a potential electrode material for energy storage applications due to its high chemical and thermal stability under harsh conditions, excellent conductivity, and durability. Moreover, SiC facilitates the faradaic redox reaction during the charge/discharge process.
However, only surface active SiC species contribute to the total capacitance, while most of the under-surface species hardly take part in the electrochemical process, leading to relatively low capacitance. As a solution to this issue, dual or multi heteroatom doping has garnered considerable focus.
Many pieces of research have demonstrated that the synergistic effect of heteroatom doping enhances the overall capacitance of the electrode material. Hence, nitrogen-containing functional groups such as pyrrolic-N species as the electrochemically active sites are found to trigger the pseudo-capacitance of the electrode material. Moreover, pyrrolic-N species tend to increase the wettability and conductivity of the carbon matrix due to the generation of a more polarized surface, thus resulting in the better transfer of electrolyte ions into the porous structure of the carbon matrix.
How was the Electrode Material Fabricated?
Two types of bamboo viz. drocalamopsis and pubsescens were ground and carbonized at high temperature to obtain two bamboo-based carbon materials viz. SNC-1 and SNC-2, respectively. Then, the respective inactivated carbon materials were activated using potassium hydroxide (KOH) to achieve activated carbon materials viz. SNAC-1 and SNAC-2. Activated carbon material obtained from natural wood was termed NAC.
To fabricate the anodes, SNAC-1, SNAC-2, SNC-1, SNC-2, and NAC were separately mixed with acetylene black and polyvinylidene fluoride (PVDF), followed by coating onto nickel foam and drying.
What was the Result?
Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM ) analysis show that the SNAC-1 has a straw-shape with two 2D plates like morphology Moreover, it shows the presence of inherent interconnected ionic channels with a rectangular plate-like morphology and highly porous structure, which facilitates the diffusion and transfer of the electrolyte ions.
The XRD patterns show that the peak intensity ratios (ID/IG) of SNAC-1 (1.04) and SNAC-2 (0.98) are higher than NAC (0.94) and lower than SNC-1 (1.17). These results indicate that despite the insertion of structural defects by the inherent SiO2 functional groups, the degree of graphitization of the carbon material is improved due to the activation process with the assistance of KOH and SiO2 nanoparticles.
The inductively coupled plasma mass spectrometry (ICP-MS) analysis demonstrates that SNAC-1 contains high silicon species (31.12 mg/g) as compared to that of SNAC-2 (21.49 mg/g), SNC-1 (16.24 mg/g), and SNC-2 (15.54 mg/g) SiO2 contents, respectively. N2 adsorption-desorption isotherms show that SNAC-1 has a high BET surface area of 1789 m2/g compared to SNAC-2 (1732 m2/g), SNC-1 (227 m2/g), and SNC-2 (196 m2/g). The high BET surface area indicates high charge storage capability for EDCLs.
The linear symmetric curves in galvanostatic charge/discharge (GCD) indicate that the SNAC-1 possesses good reversibility and excellent specific capacitance (369 F/g at 0.5 A/g) as compared to SNAC-2 (271 F/g at 0.5 / g), SNC-1 (158 F/g at 0.5 A/g), SNC-2 (73 F/g at 0.5 A/g), and NAC (232 F/g at 0.5 A/g).
The SNAC-1 delivers the highest electrochemical surface area under the cyclic voltammetry CV curves, implying the highest specific capacitance of 257 F/g at 5 mV/s as compared to SNAC-2 (220 F/s), NAC (221 F/s), SNC-1 (140 F/s), and SNC-2 (98 F/s).
The electrochemical impedance spectroscopy (EIS) analysis demonstrates that the SNAC-1 electrodes possess enhanced electrochemical performance than the SNAC-2. From the Nyquist plot, SNAC-1 has very low resistance (0.54 Ω) as compared to SNAC-2 (0.74 Ω), SNC-1 (1.56 Ω), SNC-2 (1.75 Ω), and NAC (1.10 Ω).
Thus, this work illustrates the potential future applications of bamboo-based bio-carbons as energy storage devices and also provides an effective method for the preparation of SiC and pyrrolic-N dual-doped carbon materials.
S. Abbas, C. Lin, Z. Hua, Q. Deng, H. Huang, Y. Ni, S. Cao, X. Ma, Bamboo-derived carbon material inherently doped with SiC and nitrogen for flexible supercapacitors, Chemical Engineering Journal, 2021, 133738, ISSN 1385-8947. https://www.sciencedirect.com/science/article/pii/S1385894721053122?via%3Dihub