Large-Area High-Quality AB-Stacked Bilayer Graphene on h-BN/Pt Foil by Chemical Vapor Deposition

Qian, Yongteng,Kang, Dae Joon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.34

<P>Large-area, high-quality bilayer graphene (BLG) has attracted great interest because of its immense potential for many viable applications. However, its growth is still greatly limited owing to its small size and low carrier mobility. In this article, we report the successful growth of large-area, high-quality AB-stacked BLG on hexagonal boron nitride (h-BN)/Pt foil by chemical vapor deposition (CVD). Optical microscopy and scanning electron microscopy observations reveal the formation of uniform and continuous BLG films with sizes of up to 500 μm, which are 4-5 times larger than those reported elsewhere for CVD-grown BLG films. A large carrier mobility of up to 9000 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP> is observed for the BLG films grown on h-BN/Pt foils under ambient conditions. We also propose a plausible growth mechanism of BLG growth on h-BN/Pt foils. Our findings will contribute for the better understanding of the fundamental BLG physics and the development of BLG-based devices.</P> [FIG OMISSION]</BR>

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation

Qian, Yongteng,Kang, Dae Joon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.38

<P>Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 μA cm<SUP>-2</SUP>, resulting in an ultrahigh power density of 6.22 mW cm<SUP>-2</SUP>. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.</P> [FIG OMISSION]</BR>

A stable and highly efficient visible-light-driven hydrogen evolution porous CdS/WO₃/TiO₂ photocatalysts

Qian, Yongteng,Yang, Mengke,Zhang, Fangfang,Du, Jimin,Li, Kaidi,Lin, Xialing,Zhu, Xinrui,Lu, Yayun,Wang, Weimin,Kang, Dae Joon Elsevier 2018 Materials characterization Vol.142 No.-

<P><B>Abstract</B></P> <P>It is well known that both catalytic efficiency and stability are the two important parameters of photocatalysts for visible-light-driven hydrogen production reactions. However, light-driven hydrogen evolution based applications still suffer from sluggish reaction kinetics due to the lack of high-performance photocatalysts. In this paper, we successfully synthesized a ternary porous CdS/WO<SUB>3</SUB>/TiO<SUB>2</SUB> photocatalyst with high efficiency and stability via two-stage approach. The as-prepared samples are characterized by XRD, FESEM, EDS, TEM, XPS, and UV–Vis, respectively, which illustrated that the CdS and WO<SUB>3</SUB> moieties are in-situ formed inside the porous TiO<SUB>2</SUB>. Particularly, the photocatalytic hydrogen (H<SUB>2</SUB>) evolution rate of such ternary 8% CdS/WO<SUB>3</SUB>/TiO<SUB>2</SUB> (molar ration of CdS:WO<SUB>3</SUB>:TiO<SUB>2</SUB> = 8:8:100) photocatalyst ranges up to 2106 μmol h<SUP>−1</SUP> g<SUP>−1</SUP> under visible-light irradiation, which is higher than that of pure TiO<SUB>2</SUB> and other binary (CdS/TiO<SUB>2</SUB> and WO<SUB>3</SUB>/TiO<SUB>2</SUB>) porous photocatalysts. The superior H<SUB>2</SUB> evolution efficiency can be attributed to the coexistence of CdS and WO<SUB>3</SUB> in porous TiO<SUB>2</SUB> which can promote the interfacial charge transfer and separation as well as extend the light absorption up to the visible range.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly efficient and stable photocatalytic activity of CdS/WO<SUB>3</SUB>/TiO<SUB>2</SUB> photocatalysts were synthesized by a two-step method. </LI> <LI> CdS and WO<SUB>3</SUB> inlaid on porous TiO<SUB>2</SUB> can extend the light absorption and enhance photogenerated electron-hole pairs separation. </LI> <LI> The porous structure can provide more reaction active sites and improve photoproduced-electrons and holes transport speed. </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced electrochemical performance of porous Co-doped TiO₂ nanomaterials prepared by a solvothermal method

Qian, Yongteng,Du, Jimin,Kang, Dae Joon Elsevier 2019 Microporous and mesoporous materials Vol.273 No.-

<P><B>Abstract</B></P> <P>Highly porous nanostructures having large specific surface areas are very desirable for electrochemical supercapacitors to achieve a large energy storage capacity. We synthesized porous Co-doped TiO<SUB>2</SUB> nanostructures with an average diameter of 450 nm through a simple solvothermal method by using tetrabutyl titanate and cobalt acetate as precursors and polystyrene beads as templates. The optimized 7% Co-doped TiO<SUB>2</SUB> nanostructures-based supercapacitor electrodes exhibited a specific capacitance of 352 F g<SUP>-1</SUP> at a current density of 0.5 A g<SUP>−1</SUP> while retaining a capacity of 97.2% after 3000 cycles. This excellent electrochemical performance may be ascribed to the synergistic effects originating from conductivity enhancement of TiO<SUB>2</SUB> through optimized Co-doping and larger specific surface areas rendered by structural porosity, when compared to the undoped TiO<SUB>2</SUB> samples. Our results suggest that porous Co-doped TiO<SUB>2</SUB> nanostructures can be explored for potential electrochemical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of porous Co-doped TiO<SUB>2</SUB> nanostructures by a simple sol–gel method. </LI> <LI> Conductivity enhancement of TiO<SUB>2</SUB> through optimized Co-doping. </LI> <LI> More charge transfer pathways and reaction active sites owing to porosity. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Controlled synthesis of nanoplate, nanoprism and nanopyramid-shaped CdSe decorated on porous TiO₂ photocatalysts for visible-light-driven hydrogen evolution

Yang, Mengke,Qian, Yongteng,Du, Jimin,Yuan, Sijie,Wang, Sijia,Zhu, Xinrui,Lin, Xialing,Li, Kaidi,Li, Sujuan,Kang, Dae Joon Elsevier 2018 Ceramics international Vol.44 No.11

<P><B>Abstract</B></P> <P>Herein, we report a successful synthesis of porous TiO<SUB>2</SUB> monoliths decorated with unique nanoplate, nanoprism, and nanopyramid-shaped CdSe particles through a mild selenylation of CdO embedded inside porous TiO<SUB>2</SUB> monoliths via a hydrothermal method in a very controlled manner. Compared with pure TiO<SUB>2</SUB>, as-synthesized CdSe/TiO<SUB>2</SUB> photocatalyst not only enhances light absorption but also leads to a highly efficient charge-carrier separation. Particularly, the nanoplate-shaped 7% CdSe/TiO<SUB>2</SUB> photocatalyst (molar percentages of CdSe to TiO<SUB>2</SUB> is 7:100) exhibits an exceptional hydrogen evolution rate up to 3650 μmol h<SUP>−1</SUP> g<SUP>−1</SUP> without resorting to any noble-metal co-catalysts under visible-light irradiation owing to synergistic effects envisaged by a rational material design. Our results may provide a useful strategy to develop a highly-efficient visible-light-driven hydrogen production system via water splitting.</P>

Porous NiCo2S4 Networks as Electrodes for Electrochemical Supercapacitors

Jimin Du,Kaidi Li,Yongteng Qian,Mengke Yang,Huiming Wang,Wen He,Viyada Harnchana 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.12

Porous NiCo2S4 networks have been successfully synthesized by a facile one-pot solvothermal method without the use of any surfactant or template. Crystal structure, morphology, composition and surface area of the as-synthesized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and Brunauer– Emmet–Teller techniques. Owing to their porous nature and small crystalline size, the as-prepared NiCo2S4 networks based supercapacitor electrodes showed a high specific capacitance of 1250 F · g-1 at 1 A · g-1, and excellent cycling stability with the retention capacity of 70.3% after 5000 cycles in the KOH aqueous solution electrolyte.