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Hyeon, Yuhwan,Jung, Su-Ho,Jang, Wonseok,Kim, Mansu,Kim, Byung-Sung,Lee, Jae-Hyun,Nandanapalli, Koteeswara Reddy,Jung, Namgee,Whang, Dongmok American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.5
<P>In MoS<SUB>2</SUB>-carbon composite catalysts for hydrogen evolution reaction (HER), the carbon materials generally act as supports to enhance the catalytic activity of MoS<SUB>2</SUB> nanosheets. The carbon support provides a large surface area for increasing the MoS<SUB>2</SUB> edge site density, and its physical structure can affect the electron transport rate in the composite catalysts. However, despite the importance of the carbon materials, direct observation of the effects of the physical properties of the carbon supports on the HER activity of MoS<SUB>2</SUB>-carbon composite catalysts has been hardly reported. In this work, we conduct an experimental model study to find the fundamental and important understanding of the correlation between the structural characteristics of carbon supports and the HER performance of MoS<SUB>2</SUB>-carbon composite catalysts using surface-modified graphitic carbon shell (GCS)-encapsulated SiO<SUB>2</SUB> nanowires (GCS@SiO<SUB>2</SUB> NWs) as support materials for MoS<SUB>2</SUB> nanosheets. The surface defect density and the electrical resistance of GCS@SiO<SUB>2</SUB> NWs are systematically modulated by control of H<SUB>2</SUB> gas flow rates during the carbon shell growth on the SiO<SUB>2</SUB> NWs. From in-depth characterization of the model catalysts, it is confirmed that the intrinsic catalytic activity of MoS<SUB>2</SUB>-carbon composites for the HER is improved linearly with the conductance of the carbon supports regardless of the MoS<SUB>2</SUB> edge site density. However, in the HER polarization curve, the apparent current density increases in proportion to the product of the number of MoS<SUB>2</SUB> edge sites and the conductance of GCS@SiO<SUB>2</SUB> NWs.</P> [FIG OMISSION]</BR>
Low-temperature wafer-scale growth of MoS<sub>2</sub>-graphene heterostructures
Kim, Hyeong-U,Kim, Mansu,Jin, Yinhua,Hyeon, Yuhwan,Kim, Ki Seok,An, Byeong-Seon,Yang, Cheol-Woong,Kanade, Vinit,Moon, Ji-Yun,Yeom, Geun Yong,Whang, Dongmok,Lee, Jae-Hyun,Kim, Taesung Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.470 No.-
<P><B>Abstract</B></P> <P>In this study, we successfully demonstrate the fabrication of a MoS<SUB>2</SUB>-graphene heterostructure (MGH) on a 4 inch wafer at 300 °C by depositing a thin Mo film seed layer on graphene followed by sulfurization using H<SUB>2</SUB>S plasma. By utilizing Raman spectroscopy and high-resolution transmission electron microscopy, we have confirmed that 5–6 MoS<SUB>2</SUB> layers with a large density of sulfur vacancies are grown uniformly on the entire substrate. The chemical composition of MoS<SUB>2</SUB> on graphene was evaluated by X-ray photoelectron spectroscopy, which confirmed the atomic ratio of Mo to S to be 1:1.78, which is much lower than the stoichiometric value of 2 from standard MoS<SUB>2</SUB>. To exploit the properties of the nanocrystalline and defective MGH film obtained in our process, we have utilized it as a catalyst for hydrodesulfurization and as an electrocatalyst for the hydrogen evolution reaction. Compared to MoS<SUB>2</SUB> grown on an amorphous SiO<SUB>2</SUB> substrate, the MGH has smaller onset potential and Tafel slope, indicating its enhanced catalytic performance. Our practical growth approach can be applied to other two-dimensional crystals, which are potentially used in a wide range of applications such as electronic devices and catalysis.</P> <P><B>Highlight</B></P> <P> <UL> <LI> Practical growth for 2D MoS<SUB>2</SUB>-graphene heterostructure (MGH) was introduced. </LI> <LI> Low-temperature sulfurization of Mo thin film was realized by H<SUB>2</SUB>S plasma. </LI> <LI> As-grown MoS<SUB>2</SUB> film on graphene naturally contains large number of active sites. </LI> <LI> The MGH was shown enhanced electrocatalytic performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>