【公開日：2025.05.01】【最終更新日：2025.02.21】

課題データ / Project Data

課題番号 / Project Issue Number

23NM5195

利用課題名 / Title

Ultra-High Surface Area Carbon Materials Design for Energy Storage

利用した実施機関 / Support Institute

物質・材料研究機構 / NIMS

機関外・機関内の利用 / External or Internal Use

内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）加工・デバイスプロセス/Nanofabrication（副 / Sub）計測・分析/Advanced Characterization

【重要技術領域 / Important Technology Area】（主 / Main）量子・電子制御により革新的な機能を発現するマテリアル/Materials using quantum and electronic control to perform innovative functions（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

2D heterostructures, Na ion capacitor, Energy storage

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)

Lok Kumar Shrestha

所属名 / Affiliation

物質・材料研究機構

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 Fujii

利用形態 / Support Type

（主 / Main）技術補助/Technical Assistance（副 / Sub）,機器利用/Equipment Utilization

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

NM-202：硬X線光電子分光分析装置（HAX-PES/XPS）
NM-648：FE-SEM+EDX [SU8000]

報告書データ / Report

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

The 2D WO₃/WSe₂ electrode demonstrates exceptional Na+ storage, with a specific capacitance of 378.1 F g⁻¹ at 1 A g⁻¹, excellent rate capability, and long-lasting cycling durability over 10,000 cycles. The full cell comprising WO₃/WSe₂ as the negative and MnSe/MnSe₂ as the positive electrode achieved a peak energy density of 82.1 Wh kg⁻¹ at a power density of 1873.5 W kg⁻¹, along with high-rate capability and long-cycle durability.

実験 / Experimental

　Synthesis of WSe2 nanoflakesWSe2 nanoflakes were grown on CF substrate through the selenization of WO3. A typical synthesis protocol involves two steps. The first is the synthesis of WO3 nanostructures on CF using the hydrothermal method, according to our previous report. 0.025 M Na2WO4.2H2O was dissolved in 30 mL DI water under constant magnetic stirring for 110 min to get a transparent solution. Afterward, 3 M HCl solution was added dropwise until the pH of the solution turned to ~3. At this stage, the transparent solution turns to a slight yellow. After stirring for 15 min, 0.05 M NaCl was added to the reaction solution, and then the whole solution was transferred to a 40 mL Teflon-lined stainless steel autoclave. The well-cleaned and dried piece of CF substrate (2 X 2) cm was placed into the Teflon liner, and then the autoclave was kept for hydrothermal reaction in an oven at 180 ºC for 12 h. Subsequently the autoclave cooled to room temperature, the CF substrate with deposited material was removed and washed several times with DI water and ethanol and dried in a vacuum oven at 70 ºC overnight.              The selenization of WO3 on CF to prepare WSe2 nanoflakes was performed at four different temperatures, 600 ºC, 700 ºC, 800 ºC, and 900 ºC. The piece of WO3 on CF was placed in one quartz boat at the center of the tube furnace, and a second quartz boat with 0.5 gm Se powder was kept on the front side of the tube furnace under N2 gas flow 100 sccm. The temperature of the tube furnace was varied from 600 – 900 ºC with a heating rate of 10 ºC min-1 for 2h. The N2 gas carries Se vapors to the surface of WO3 where WSe2 nanoflake growth occurs. When the tube furnace was naturally cooled down slowly to room temperature, WSe2 nanoflakes on CF were collected.
　Synthesis of MnSe nanowires　 MnSe nanowires were directly grown on CF substrate through a one-pot hydrothermal method. Se (0.1 gm) powder was dissolved in 30 mL of DI water using a bath sonicator for 10 min and kept for constant stirring on a magnetic stirrer. 0.1 gm NaBH4 was added to the Se powder solution, followed by 0.05 M MnCl2.4H2O. The reaction solution was kept stirring for another 10 min and then transferred to a 40 mL Teflon-lined stainless steel autoclave. The well-cleaned and dried piece of CF substrate (2 X 2) cm was placed into the Teflon liner, and then the autoclave was kept for hydrothermal reaction in an oven at 180 ºC for 12 h. When the autoclave cooled to room temperature, the CF substrate with deposited material was removed and washed several times with DI water and ethanol and dried in a vacuum oven at 70 ºC overnight.

結果と考察 / Results and Discussion

　The 2D WO₃/WSe₂ heterostructures were directly grown on carbon fiber substrate as described above and characterized using SEM/EDS. Scanning electron microscopy (SEM) was used to analyze the surface morphology of prepared materials, offering insights into the assembly of nanosheets on carbon fiber (CF). Following the selenization process, WO₃ stacked sheets were transformed into ultrathin nanoflakes, as depicted in Figure 1b-n. Notably, the CF substrate appeared radially covered with arrays of WO₃/WSe₂ nanoflakes, with each 2D nanosheet distinctively separated and firmly adhering to the CF. Both WO₃/WSe₂-1 and WO₃/WSe₂-2 exhibited similar ultrathin nanoflake morphologies (Figure 1b-e). At high magnification, it became clear that each nanoflake was separated, forming a star-like nanoarchitecture having lateral size 500 to 700 nm and a thickness of less than 5 nm. These nanoflakes effectively alleviate the stacking of Se-W-Se layers, facilitating facile Na-ion transport. The ultrathin appearance of these nanoflakes suggests that the presence of WO₃ in the material, i.e., heterophase, dynamically influences nanoflake thickness reduction. Such ultrathin nanoflakes hold promise as electrodes ASIC, offering a large electroactive surface area, superior stability, and plenty of interspace for Na-ion access, enhancing charge storage properties and overall electrochemical performance. Comparatively, the nanoflake thickness of WSe₂-3 (Figure 1f-g) appeared larger, suggesting that temperature has kinetic influences on nanoflake thickness. Further increase in selenization temperature for WSe₂ -4(Figure 1h-i) resulted in a gradual decrease of nanoflake size and an increase in thickness, indicating that high-temperature selenization promotes nanoflake miniaturization, ultimately leading to the formation of dense nanosheets. Energy dispersive X-ray spectroscopy (EDS) (Figure 1j-n) mapping images for WO₃/WSe₂-2, revealing the consistent dispersal of W, Se, and O elements on conductive CF substrate. 

図・表・数式 / Figures, Tables and Equations

Figure 1 a) Two-step synthesis protocol of the WO₃/WSe₂ heterostructures on CF. low-and high-magnification FESEM images of WO₃/WSe₂ heterostructures, b-c) WO₃/WSe₂-1, d-e) WO₃/WSe₂-2, f-g) WSe₂-3 and h-i) WSe₂-4. j-n) FESEM-EDS mapping images for W, Se, C, and O elements in WO₃/WSe₂-2.

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

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. Pragati A. Shinde, Unveiling the Nanoarchitectonics of Interfacial Electronic Coupling in Atomically Thin 2D WO₃/WSe₂ Heterostructure for Sodium‐Ion Storage in Aqueous System, Advanced Functional Materials, 34, (2024).
   DOI: https://doi.org/10.1002/adfm.202406333
   

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