Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, China
Nano-Micro Conference, 2017, 1, 01025
Published Online: 14 October 2017 (Abstract)
Advanced materials for electrocatalytic andphotoelectrochemical water splitting are central to the area of renewable energy. Recently, two dimensional layered materials of MX2 (M: Mo, W; X:S, Se, etc.) have emerged as a new kind of catalysts for such applications. Our group have reported the direct synthesis of high-quality, domain size tunable, strictly monolayer MoS2 flakes on commercially available Au foils by a chemical vapor deposition (CVD) method. The nano-sized triangular MoS2 flakes on Au foils are proven to be excellent electrocatalysts for hydrogen evolution reaction (HER), featured by a rather low Tafel slope (61 mV/dec) and a relative high exchange current density (38.1 μA/cm2). The excellent electron coupling between MoS2 and Au foils is considered to account for the extraordinary HER activity . Furthermore, via a facile all-CVD approach, we have also demonstrated the direct growth of monolayer MoS2 on graphene (MoS2/Gr) over Au foils [2,3]. A dramatic decrease of the bandgap from ~2.20 to ~0.30 eV was detected at the domain edge of MoS2 within a lateral distance of ~6 nm, as evidenced by STM/STS observations. The edges of monolayer MoS2 nano-sheets were thus served as narrow-gapquantum wires, which can greatly facilitate the electrocatalytic property of MoS2 in HER . Meanwhile, we also synthesized either MoS2/WS2 or WS2/MoS2 vertical heterostructures on Au foils by a growth-temperature-mediated, selective two-step CVD strategy. Relative enhancement or reduction in the photocatalytic activities were observed for MoS2/WS2 and WS2/MoS2 in HER under illumination, respectively. This is explained from the type-II band alignment of the MoS2/WS2 stack that enables effective electron-hole separation and fast electron transfer kinetics, as well as directional electron flow from electrode to catalytically active sites . The abovementioned efforts are expected to establish the internal relationship between the metallic edge states of MoS2 and its HER performances, as well as the advantage of MX2/MX2 vertical stacks in photocatalytic HER applications.
 J. P. Shi; D. L. Ma; G.-F. Han; Y. Zhang; Q. Q. Ji; T. Gao; J. Y. Sun; X. J. Song; C. Li; Y. S. Zhang; X.-Y. Lang; Y. F. Zhang; Z. F. Liu, Controllable Growth and Transfer of Monolayer MoS2 on Au Foils and Its Potential Application in Hydrogen Evolution Reaction. ACS Nano. 8, 10196–10204 (2014). doi:10.1021/nn503211t
 J. P. Shi; M. X. Liu; J. X. Wen; X. B. Ren; X. B. Zhou; Q. Q. Ji; D. L. Ma; Y. Zhang; C. H. Jin; H. J. Chen; S. Z. Deng; N. S. Xu; Z. F. Liu; Y. F. Zhang, All Chemical Vapor Deposition Synthesis and Intrinsic Bandgap Observation of MoS2/Graphene Heterostructures. Advanced Materials. 27, 7086–7092 (2015). doi:10.1002/adma.201503342
 J. P. Shi; Q. Q. Ji; Z. F. Liu; Y. F. Zhang, Recent Advances in Controlling Syntheses and Energy Related Applications of MX2 and MX2/Graphene Heterostructures. Advanced Energy Materials. 6, 1600459 (2016). doi:10.1002/aenm.201600459
 J. P. Shi; X. B. Zhou; G.-F. Han; M. X. Liu; D. L. Ma; J. Y. Sun; C. Li; Q. Q. Ji; Y. Zhang; X. J. Song; X.-Y. Lang; Q. Jiang; Z. F. Liu; Y. F. Zhang, Narrow-Gap Quantum Wires Arising from the Edges of Monolayer MoS2 Synthesized on Graphene. Advanced Materials Interfaces. 3, 1600332 (2016). doi:10.1002/admi.201600332
 J. P. Shi; R. Tong; X. B. Zhou; Y. Gong; Z. P. Zhang; Q. Q. Ji; Y. Zhang; Q. Y. Fang; L. Gu; X. N. Wang; Z. F. Liu; Y. F. Zhang, Temperature-Mediated Selective Growth of MoS2/WS2 and WS2/MoS2 Vertical Stacks on Au Foils for Direct Photocatalytic Applications. Advanced Materials. 28, 10664–10672 (2016). doi:10.1002/adma.201603174
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