【公開日：2023.08.01】【最終更新日：2023.05.11】
課題データ / Project Data
課題番号 / Project Issue Number
22SH0011
利用課題名 / Title
One-step hydrothermal synthesis of manganese oxide nanosheets with graphene quantum dots for high-performance supercapacitors
利用した実施機関 / Support Institute
信州大学
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）物質・材料合成プロセス/Molecule & Material Synthesis（副 / Sub）-
【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）革新的なエネルギー変換を可能とするマテリアル/Materials enabling innovative energy conversion
キーワード / Keywords
supercapacitors, graphene oxide
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)
WANG Zhipeng
所属名 / Affiliation
Jiangxi Normal University
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
利用形態 / Support Type
（主 / Main）共同研究/Joint Research（副 / Sub）-
利用した主な設備 / Equipment Used in This Project
報告書データ / Report
概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)
With the increasing demands of energy storage and conversion (ESC) devices to address fossil fuel shortages and environmental concerns, many efforts have been made to develop new ESC devices with excellent energy and power densities as well as long lifetime in order to achieve the future development of low-carbon and sustainable economy . Among them, supercapacitors (SCs) have attracted great research attention in recent years due to their fast charge and discharge rate, high power density, long durability, and environmental friendliness. However, low energy density of SCs limited their wider applications. According to the equation of SC energy density, E=1/2CV2, in which C means the specific capacitance that relates to the electrode materials, and V is the operation voltage that involves the electrolytes, there are two strategies for improving the energy density. One of the approaches is to choose the electrolyte with wider voltage window for SCs, e.g. organic electrolytes, or ionic liquids. But, organic electrolytes are usually hazardous and flammable, while ionic liquids are too expensive. Thus, researchers prefer to search for electrode materials with high specific capacitance that can work in aqueous electrolytes.
実験 / Experimental
In the typical synthesis procedure, a certain amount of KMnO4 (0.5-4.0 mmol) was mixed with 1 mg mL-1 GO aqueous solution (75 mL) under stirring to form a homogenous solution. Next, the total solution was transferred into a stainless-steel autoclave with a capacity of 100 mL, sealed and heated at 180℃ for 1 h. Then the autoclave was cooled to room temperature naturally. Next, the resulting product was firstly filtered through Buchner funnel to obtain the upper solid and the lower filtrate containing GQDs. Subsequently, the solid product was obtained by freeze-drying for 24 h, which is referred as the composite of MnO2/GQDs (named as GQDs@MnO2), and further utilized as the SC electrode. For a comparison, the KMnO4 solution without GO was also hydrothermally reacted at the same conditions. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images were captured by using SU-8020 (Hitachi, Japan) and Merlin Compact (ZEISS, Germany), and JEM-2100 (JEOL, Japan), respectively. X-ray diffractometer (XRD) was performed by using the Rigaku diffractometer with Cu Kα radiation source at scanning rate of 4o min-1 to determine the phase of the products. Raman spectrum was obtained through LabRAM HR Evolution (Horiba, France) Raman spectroscopy with a laser of 514 nm. X-ray photoelectron spectroscopy (XPS) was obtained by using Thermo Scientific K-Alpha electron spectrometer with a monochromatic Al Kα as the X-ray source. The FT-IR spectrum was obtained by using FTIR-spectrometer Spectrum One (PerkinElmer, USA). Photoluminescence (PL) was recorded with a fluorospectrophotometer-F97 (Lengguang, China). Atomic force microscope (AFM) image was carried out by using DI MultiMode-8 (Bruker, USA). Thermogravimetric analysis (TGA) was performed on TG-6300 (Seiko, Japan).
結果と考察 / Results and Discussion
MnO2 is considered to be one of the promising electrode materials for supercapacitors thanks to its ultra-high theoretical capacitance value, but its actual electrochemical performance is not ideal due to its low electrical conductivity and poor stability. Herein, we find that the supercapacitor performance of graphene quantum dots (GQDs)@MnO2 composite is superior to that of the pure MnO2 electrode. The GQDs@MnO2 composite is obtained by a highly efficient one-step hydrothermal method, in which KMnO4 reacts with graphene oxide to produce MnO2 nanosheets anchored with GQDs in a short time. The GQD@MnO2 electrode presents high specific capacitance of 246 F g-1 at a scan rate of 1 mV s-1 in Na2SO4 electrolyte, and the as-assembled asymmetric supercapacitor (GQDs@MnO2//activated carbon) exhibits superior energy density of 29.9 Wh kg-1 at power density of 538.0 W kg-1, and good cycling performance (81.3% retention after 8000 cycles) that was far better than that of pure MnO2-based supercapacitor. The excellent supercapacitor performance of GQDs@MnO2 composite results from its enhanced electrical conductivity, good wettability and abundant available contact sites for aqueous electrolyte, which are ascribed to the intrinsic high electrical conductivity as well as the quantum confinement and edge effects of GQDs.
図・表・数式 / Figures, Tables and Equations
その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)
Y. Zhu, Z. Huang, X. Huang, Y. Li, H. Li, B. Zhou, J. Liu, K. Xu, M. Wang, H. Ogata, G.J.H. Melvin, J. Ortiz-Medina, W. Gong, Z. Wen, M. Terrones, M. Endo, Z. Wang, Journal of Energy Storage 62, (2023) 106948.
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)
-
Yangjun Zhu, One-step hydrothermal synthesis of manganese oxide nanosheets with graphene quantum dots for high-performance supercapacitors, Journal of Energy Storage, 62, 106948(2023).
DOI: https://doi.org/10.1016/j.est.2023.106948
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