中央研究院 原子與分子科學研究所

Employing direct Z-scheme semiconductor heterostructures in photocatalysis offers efficient charge carrier separation and isolation of both redox reactions, thus beneficial to reduce CO₂ into solar fuels. Here, a ZnS/ZnIn₂S₄ heterostructure, comprising cubic ZnS nanocrystals on hexagonal ZnIn₂S₄ (ZIS) nanosheets, is successfully fabricated in a single-pot hydrothermal approach. The composite ZnS/ZnIn₂S₄ exhibits microstrain at its interface with an electric field favorable for Z-scheme. At an optimum ratio of Zn:In (~ 1:0.5), an excellent photochemical quantum efficiency of around 0.8% is reached, nearly 200-fold boost compared with pristine ZnS. Electronic levels and band alignments are deduced from ultraviolet photoemission spectroscopy and UV-Vis. Evidence of the direct Z-scheme and carrier dynamics is verified by photo-reduction experiment, along with photoluminescence (PL) and time-resolved PL. Finally, diffuse-reflectance infrared Fourier transformed spectroscopy explores the CO₂ and related intermediate species adsorbed on the catalyst during the photocatalytic reaction. This microstrain-induced direct Z-scheme approach opens a new pathway for developing next-generation photocatalysts for CO₂ reduction.

Nonnoble metal catalysts are low-cost alternatives to Pt for the oxygen reduction reactions (ORRs), which have been studied for various applications in electrocatalytic systems. Among them, transition metal complexes, characterized by a redox-active single-metal-atom with biomimetic ligands, such as pyrolyzed cobalt–nitrogen–carbon (Co–N x /C), have attracted considerable attention. Therefore, we reported the ORR mechanism of pyrolyzed Vitamin B12 using operando X-ray absorption spectroscopy coupled with electrochemical impedance spectroscopy, which enables operando monitoring of the oxygen binding site on the metal center. material design strategies for high-performance electrocatalysts for fuel cell applications. Furthermore, the charge transfer mechanism between the catalyst and reactant enables further Co–O species formation. These experimental findings, provide insight into metal active-site geometry and structural evolution during ORR, which could be used for developing material design strategies for high performance electrocatalysts for fuel cell applications.

In this study, a self-capping vaporliquid-solid reaction is proposed to fabricate large-grain, continuous MoS2 films. An intermediate liquid phase-Na2Mo2O7 is formed through a eutectic reaction of MoO3 and NaF,followed by being sulfurized into MoS2. The as-formed MoS2 seeds function as a capping layer that reduces the nucleation density and promotes lateral growth. By tuning the driving force of the reaction, large mono/bilayer (1.1 mm/200 μm) flakes or full-coverage films (with a record-high average grain size of 450 μm) can be grown on centimeter-scale substrates. The field-effect transistors fabricated from the full-coverage films show high mobility (33 and 49 cm2V-1s-1 for the mono and bilayer regions) and on/off ratio (1 ~ 5 × 108) across a 1.5 cm × 1.5 cm region.

當前綠能與儲能等研究領域中，設計高導電金屬有機骨架聚合物(MOF)是極具應用潛力的主題。本研究藉由設計銅硫(–Cu–S–)n二維平面於MOF結構之策略來實現高導電MOF之特性。利用水熱法，有機配基6,6’-dithiodinicotinXic acid因原位裂解S–S鍵形成6-mercaptonicotinic acid (1,6-Hmna)與6-mercaptonicotinate (6-mn)，並與硝酸銅反應合成MOF化合物{[Cu2(6-Hmna)(6-mn)]·NH4}n。經各種材料分析發現該化合物具(–Cu–S–)n二維平面結構、低活化能（6 meV）、小帶隙（1.34 eV）、及高電導率（10.96 S cm−1）等特性，適用於電池、熱電、超級電容器等相關領域。本研究是由中研院化學所呂光烈、中研院原分所陳貴賢、台大凝態科學中心林麗瓊與台北科大化工系曾添文等教授共同合作，以及台大凝態科學中心林倫年、台灣科大應用科技研究所陳瑞山與清大工程與系統科學系陳福榮等教授協同合作成果，論文已於近期發表於 Nature Communications 期刊  (2019, 10, 1721) 。

Carbon-doped SnS₂ (SnS₂-C) metal dichalcogenide nanostructure has been synthesized using a hydrothermal technique, which exhibits a highly active and selective photocatalytic conversion of CO₂ to hydrocarbons under visible-light, attaining a photochemical quantum efficiency of above 0.7%. The SnS₂ -C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO₂ reduction under visible light.

In this study, copper nanoparticles (Cu-NPs) decorated graphene oxide (Cu/GO) has been used to enhance photocatalytic CO2 reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (~4-5 nm) in GO hybrid predominately enhance the photocatalytic activity of GO, which is primarily due to the suppression of electron-hole pair recombination, further reduction of GO's bandgap, and modification of their work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. Strong metal-support interaction is also proposed to play some role in the selection of reactions and products.  More than 60 times enhancement in CO2 to fuel catalytic efficiency has been demonstrated using Cu/GO-2 (10 wt% Cu) comparative to that using pristine GO; or 240 times enhancement comparative to P25.