【公開日：2025.06.10】【最終更新日：2025.05.04】

課題データ / Project Data

課題番号 / Project Issue Number

24SH0014

利用課題名 / Title

Performance Tuning of Hemp-Derived Activated Carbon Electrodes in Aqueous Electrolytes for Supercapacitor Applications

利用した実施機関 / Support Institute

信州大学 / Shinshu Univ.

機関外・機関内の利用 / External or Internal Use

外部利用/External Use

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）計測・分析/Advanced Characterization（副 / Sub）物質・材料合成プロセス/Molecule & Material Synthesis

【重要技術領域 / Important Technology Area】（主 / Main）次世代ナノスケールマテリアル/Next-generation nanoscale materials（副 / Sub）マテリアルの高度循環のための技術/Advanced materials recycling technologies

キーワード / Keywords

ナノカーボン/ Nano carbon,ナノ多孔体/ Nanoporuous material,電子顕微鏡/ Electronic microscope,未利用資源の有効利用技術/ Technologies for effective utilization of unused resources,赤外・可視・紫外分光/ Infrared/visible/ultraviolet spectroscopy,赤外・可視・紫外分光/ Infrared/visible/ultraviolet spectroscopy

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

Winadda Wongwiriyapan

所属名 / Affiliation

School of Integrated Innovative Technology, King Mongkut's Institute of Technology Ladkrabang

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

Michiko Obata,Masatsugu Fujishige,Kenji Takeuchi

利用形態 / Support Type

（主 / Main）共同研究/Joint Research（副 / Sub）,機器利用/Equipment Utilization

利用した主な設備 / Equipment Used in This Project

SH-101：電界放出型走査電子顕微鏡
SH-004：光電子分光装置
SH-001：ダブル球面収差補正付透過型電子顕微鏡
SH-002：走査型透過電子顕微鏡
SH-009：レーザラマン分光装置

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

This manuscript investigates the synthesis and electrochemical performance of hemp-derived activated carbon (HAC) for supercapacitor electrode applications. HAC was prepared through NaOH chemical activation and its electrochemical characteristics were evaluated using three different electrolytes: acidic (H₂SO₄), neutral (Na₂SO₄), and basic (KOH). The specific surface area of HAC was found to be exceptionally high, measuring 2612 m²/g, surpassing that of commercially available AC. Surface analysis revealed the presence of oxygen functional group, which provided additional pseudocapacitive active sites. When employing 1 M H₂SO₄ as the electrolyte, HAC demonstrated a maximum specific capacitance of 594 F/g (302.4 F/cm³) at a current density of 0.3 A/g. Notably, the HAC electrode exhibited significantly higher energy density and power density, reaching values of 82 Wh/kg (135.7 mWh/cm³) and 188 W/kg (311 mW/cm³), respectively, when compared to commercial AC. These results highlight the potential of HAC as a cost-effective and high-performance electrode material, particularly when paired with H₂SO₄ as the electrolyte due to their ideal micropore/mesopore ratio for H₂SO₄ electrolyte access.

実験 / Experimental

Synthesis of hemp-derived activated carbon The synthesis of HAC was performed using a chemical activation method with NaOH. Initially, raw hemp fibers (husk and bast mixed together as received after harvest) were cut into small pieces and sieved using a 250 μm mesh. Subsequently, the sieved hemp fibers were dried at 80°C for a duration of 12 hours. The carbonization process was carried out to obtain biochar under a nitrogen atmosphere with a flow rate of 0.5 L/min, employing a ramping rate of 5 °C/min, and a temperature of 500 °C for 2 hours.  For the activation process, a mixture was prepared consisting of 1 g of biochar and NaOH at a weight ratio of biochar to NaOH 1:4. The mixture was subjected to heating at a rate of 5 °C/min under an argon atmosphere with a flow rate of 0.5 L/min, reaching a temperature of 720 °C and maintaining it for 1 hour. The resulting product was a black powder. Subsequently, the black powder was treated with 1 M HCl at 100 °C for a duration of 4 hours. The product was washed with deionized water until the pH reached 7, followed by drying at 100 °C for 12 hours. The biochar production yield after pyrolysis was approximately 35.5%, and subsequently, the activated carbon yield after the activation process was approximately 11.4% of the original hemp fibers.

結果と考察 / Results and Discussion

The morphological structure of HAC and AB520Y electrodes was characterized by FE-SEM. The image reveals that the HAC electrodes exhibit a sponge-like appearance with a porous structure that covers the entire surface. In comparison, AB520Y shows a more solid, smoother surface.  The microstructure of HAC and AB520Y is investigated using TEM. Both HAC and AB520Y exhibit a porous structure as fine and bright spots in the TEM images. In comparison, HAC has smaller and denser pores, which is in accordance with the porosity analysis (Figure 1).
The crystal structure characteristics of AB520Y and HAC are further confirmed with the X-ray diffraction (XRD) technique. The broad (002) diffraction peak at 2θ about 15–30° is attributed to amorphous carbon structures, while the weak and broad (101) diffraction peak of graphite structure is observed at 2θ about 40–50°. Raman spectra obtained from HAC and AB520Y exhibit prominent peaks at approximately 1333 and 1594 cm^-1. The peak at 1333 cm^-1 corresponds to the D band, associated with sp³-bonded carbon atoms present in defects and disorder structures. The peak at 1594 cm^-1 corresponds to the G band, indicating sp²-bonded carbon atoms in hexagonal graphitic rings. The intensity ratio of the D band to the G band, represented as I_D/I_G, provides valuable information about the structural properties of the samples. In the case of HAC, the I_D/I_G is measured to be 0.84, whereas for AB520Y, the I_D/I_G is found to be 1.13. The lower I_D/I_G value observed in HAC indicates a more ordered structure that ensure its low electrical resistance during charge-discharge process (Figure 1).
The surface chemistry of HAC and AB520Y was characterized by XPS. Comparing the two samples, HAC exhibits a higher atomic percentage of oxygen and nitrogen, measuring 7.97% and 1.23%, respectively, while AB520Y shows slightly lower values of 6.67% for oxygen and 0.73% for nitrogen. The deconvolution of the C 1s peak reveals four distinct peaks with binding energies at 284.5, 286.4, 287.8, and 289.1 eV, corresponding to different carbon species; C-C/C=C in aromatic rings, C-OH for epoxy and alkoxy groups, C=O for carbonyl groups, and O=C-OH carboxylate carbon, respectively. The relative percentages of these oxygen functional groups are higher in HAC compared to AB520Y. The higher presence of oxygen functional groups, albeit in relatively low concentrations, in HAC suggests the incorporation of hydrophilic species on the materials surface. These oxygen-rich-functional groups contribute to the hydrophilic properties of the electrodes, promoting better electrolyte wetting and enhancing ion accessibility during charge and discharge processes. Additionally, these functional groups are expected to provide additional specific capacitance to the supercapacitor, potentially enhancing its overall performance (Figure 2).
Next electrochemical performance was investigated. The CV curves exhibit a relatively rectangular shape, indicative of a dynamically reversible process, excepted for 1 M Na₂SO₄ electrolyte. Furthermore, the electrode demonstrates pseudocapacitive behaviour, characterized by a pair of redox-reduced peaks originating from rapid and reversible reactions occurring on the surface of the active material. Notably, HAC measured in 1M H₂SO₄ electrolyte exhibits the highest specific capacitance, as evidenced by its largest enclosed curve area, followed by 3M KOH and 1M Na₂SO₄, respectively. The calculated specific capacitances of HAC in 1M H₂SO₄, 3M KOH and 1M Na₂SO₄ electrolytes at a scan rate of 5 mV/s are 571 F/g (290.7 F/cm³), 413 F/g (252.3 F/cm³), 240 F/g (189.4 F/cm³), respectively. In comparison, AB520Y shows a significantly smaller enclosed curve area, suggesting a lower specific capacitance resulting from a lower surface area according to porosity analysis (292 F/g (219.3 F/cm³) at 5 mV/s). Moreover, when measured in 1M H₂SO₄ electrolyte, HAC demonstrates pseudocapacitive characteristics within the potential range of 0-0.6 V, which are suggested to be attributed to the incorporation of oxygen functional groups on the electrode surface (Figure 3).
The GCD curves of HAC displayed an almost symmetrical triangle with a small voltage drop when measured in 1M H₂SO₄ and 3M KOH, indicating highly reversible properties. These curves show a nearly linear correlation between potential and time, clearly demonstrating the electrochemical double-layer characteristics of the electrode. In contrast, HAC measured in 1M Na₂SO₄ exhibited a much larger voltage drop, indicating the high electrical resistance of the electrode, which resulted in lower charge storage efficiency. The charge storage efficiency of HAC in 1M H₂SO₄, 3M KOH, and 1M Na₂SO₄ were approximately 65%, 59% and 22%, respectively.  The slight variation of slope caused by the pseudocapacitive nature of oxygen functional groups on the surface of the electrode. This is attributed to the charge storage through the process of adsorption/desorption at the interface of the electrode and electrolyte. The sharp drop at the beginning of the discharging segment was a voltage drop due to the intrinsic electrical resistance of materials. The specific capacitances of HAC in 1M H₂SO₄, 3M KOH and 1M Na₂SO₄ electrolytes at a current density of 0.3 A/g are 594 F/g (302.4 F/cm³), 436 F/g (266.3 F/cm³), and 304 F/g (239.9 F/cm³), respectively.  Notably, the specific capacitance of HAC in 1M H₂SO₄ is the highest, with a value almost 2 times higher than that of AB520Y measured in the same electrolyte (295 F/g (221.5 F/cm³) at 0.3 A/g). The highest specific capacitance may be attributed to the presence of oxygen-functional groups, a high surface area, and an optimum pore size (Figure 3).  

図・表・数式 / Figures, Tables and Equations

 Figure 1. FE-SEM and TEM images of (a,c) HAC and (b,d) AB520Y. (e) XRD patterns and (f) Raman spectra of HAC and AB520Y electrodes.

Figure 2  (a) XPS survey spectra of HAC and AB520Y electrode material. High-resolution C1s XPS spectra of (b) HAC and (c) AB520Y

Figure 3 (a) Cyclic voltammetry curves of HAC electrode in different electrolytes and AB520Y electrode in 1M H₂SO₄ electrolyte at scan rate 5 mV/s. (b) galvanic charge-discharge curves of HAC electrode in different electrolytes and AB520Y electrode in 1M H₂SO₄ electrolyte at current density 0.3 A/g. 

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

The authors are also thankful to the Nanotechnology and Material Analytical Instrument Service Unit (NMIS), College of Materials Innovation and Technology (CMIT), KMITL, for their valuable assistance. Furthermore, the authors acknowledge the support received from Eastern Spectrum Group Co., Ltd., in providing the hemp raw fiber for this study.

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

1. Kanisorn Klangvijit, Optimizing Electrochemical Performance: A Study of Aqueous Electrolytes with Hemp-Derived Activated Carbon for Supercapacitors, ACS Omega, 10, 6601-6614(2025).
   DOI: 10.1021/acsomega.4c07518
   

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

特許 / Patents

特許出願件数 / Number of Patent Applications：0件
特許登録件数 / Number of Registered Patents：0件