| 研究課題/領域番号 |
16F16049
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| 研究機関 | 国立研究開発法人物質・材料研究機構 |
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研究代表者 |
葉 金花 国立研究開発法人物質・材料研究機構, 国際ナノアーキテクトニクス研究拠点, MANA主任研究者 (90230630)
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| 研究分担者 |
CHANG KUN 国立研究開発法人物質・材料研究機構, 国際ナノアーキテクトニクス研究拠点, 外国人特別研究員
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| 研究期間 (年度) |
2016-04-22 – 2018-03-31
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| キーワード | Hydrogen evolution / Photocatalysis / Non-precious metal / Monolayer / Direct exfoliation |
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| 研究実績の概要 |
This project aims at developing the new routes of high-yield production of transition metal dichalcogenide (TMDCs) monolayers with high quality and stability, and exploring their application for solar hydrogen evolution and overall water splitting.
In the past year, a novel strategy of engineering the lateral size of TMDC (MoS2 and WS2) crystals in the nanoscale to increase the fraction of edges was achieved. The proposed bulk TMDCs could be directly exfoliated in polar micromolecular solvents, even in pure water, to produce monolayer MoS2 and WS2 nanosheets in high yield. These exfoliated MoS2 (WS2) monolayers exhibited superior cocatalytic performance in the photocatalytic hydrogen evolution reaction (HER).
On the other hand, we first provided a facile and effective strategy with lithium molten salts to accurately control the different phases of MoS2 precursor at different calcination temperature. With the subsequent hydrolysis reaction of lithium salts, the precursors can be high-efficiently and swimmingly exfoliated into 2H or 1T phased monolayer MoS2. During the subsequent catalytic hydrogen evolution test, we also found the unexpected results between electro- and photo-catalytic reactions, in particular the latter of which suggest us to necessarily consider the match abilities of electronic energy level for MoS2 with proper photoharvester semiconductors.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Focusing on the proposed research plan, we have achieved the scalable synthesis of monolayer transition metal disulfides (TMDCs) and target control of phase transformation. Current results indicated that through engineering the edges of bulk TMDCs to create more exposed edge fractions, the designed bulk TMDCs can be easily exfoliated into monolayers by a simple ultrasonic method, even in the water; besides, through lithium molten salts, we can accurately control the different phases of MoS2 precursor at different calcination temperature. During the HER activity test, both 1T and 2H monolayer MoS2 and WS2 exhibited the high catalytic H2 activity, not only in electrocatalytic HER but also being as cocatalysts in photocatalytic HER. However, our research demonstrated that when as the cocatalysts over photoharvester semiconductors, the semiconductors also play the important role in the H2 evolution activity. Due to the semiconducting property for 2H-MoS2 but metallic property for 1T-MoS2, it suggests us to necessarily consider the match abilities of electronic energy level for MoS2 with proper photoharvester semiconductors.
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| 今後の研究の推進方策 |
Monolayer MoS2 with more exposed active sites is known as the most active non-precious metal HER catalyst reported in acid. However, their overall electrode activity is still limited, as generally only a small fraction of sites (edge sites) contibute to the reaction rate. How to activate the inert basal plane of MoS2 to significantly enhance its catalytic HER activity has become a great challenge in the following work.
In general, there are mainly two prospective ways to realize: i) phase-transformation engineering - from semiconducting 2H phase to metallic 1T phase. As we mentioned before, 1T-MoS2 has a metallic property and highly catalytic H2 activity. However, the metastable phase for 1T-MoS2 need us to explore more effective way to realize its stable structure and high activity. ii) re-organization of inert sulfur atoms - creating more active sites within inert basal plane. Through the previous reports on MoS2 based HER catalysts, it is found that the catalytic H2 activity of MoS2 with an amorphous counterpart is usually higher than that of crystalline form. The latest research indicated that the disordered structure of sulfur atoms and partial S-vacancies existed in the plane of MoS2, which would facilitate the activity of inert sulfurs. Nevertheless, exposed defects of amorphous forms simultaneously decrease the conductivity of MoS2 itself, which extremely restrict the electron mobility and decrease its catalytic activity. Thus, a comprehensive consideration of maximizing the synergistic activity for MoS2 HER is significantly important.
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