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. 2016 Feb 10:7:10672.
doi: 10.1038/ncomms10672.

Pure and stable metallic phase molybdenum disulfide nanosheets for hydrogen evolution reaction

Xiumei Geng  1 , Weiwei Sun  1 , Wei Wu  1 , Benjamin Chen  2 , Alaa Al-Hilo  1 , Mourad Benamara  3 , Hongli Zhu  4 , Fumiya Watanabe  1 , Jingbiao Cui  5 , Tar-Pin Chen  1
Affiliations

Pure and stable metallic phase molybdenum disulfide nanosheets for hydrogen evolution reaction

Xiumei Geng et al. Nat Commun. .

Abstract

Metallic-phase MoS2 (M-MoS2) is metastable and does not exist in nature. Pure and stable M-MoS2 has not been previously prepared by chemical synthesis, to the best of our knowledge. Here we report a hydrothermal process for synthesizing stable two-dimensional M-MoS2 nanosheets in water. The metal-metal Raman stretching mode at 146 cm(-1) in the M-MoS2 structure, as predicted by theoretical calculations, is experimentally observed. The stability of the M-MoS2 is associated with the adsorption of a monolayer of water molecules on both sides of the nanosheets, which reduce restacking and prevent aggregation in water. The obtained M-MoS2 exhibits excellent stability in water and superior activity for the hydrogen evolution reaction, with a current density of 10 mA cm(-2) at a low potential of -175 mV and a Tafel slope of 41 mV per decade.

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Figures

Figure 1
Figure 1. Morphology of M-MoS2 and phase identification of M-MoS2 and S-MoS2.
(a) SEM image of M-MoS2 showing the nanosheet structures. Scale bar, 100 nm. (b) Raman shift of M-MoS2 and S-MoS2. (c,d) High-resolution X-ray photoelectron spectroscopy (XPS) spectra of Mo 3d (c) and S 2p (d) for M-MoS2 and S-MoS2.
Figure 2
Figure 2. Morphology and property of M-MoS2 and S-MoS2.
(a) As-prepared M-MoS2 and S-MoS2 in water. (b) Suspension of M-MoS2 and S-MoS2 in water. (c) Ultraviolet–visible absorption of M-MoS2 and S-MoS2. (d) HRTEM image of M-MoS2. The region indicated by the squares is enlarged to show the atomic structure of M-MoS2. Scale bar, 1 nm.
Figure 3
Figure 3. Raman and structural characterization to investigate the stability of M-MoS2.
(a) Raman shift of M-MoS2 stored for 90 days at room temperature. (b) XRD patterns of wet M-MoS2, dry M-MoS2 and wet S-MoS2. (c) Low-resolution TEM image of M-MoS2. Scale bar, 10 nm. (d) HRTEM image of M-MoS2. The region indicated by the square is enlarged to show the layered structure of M-MoS2. Scale bar, 2 nm. (e) Line scan of the HRTEM image indicated by the blue line in d, indicating a layer-to-layer spacing of 0.65 nm.
Figure 4
Figure 4. HER activity of the synthesized MoS2 nanosheets.
(a) Polarization curves of the M-MoS2 and S-MoS2 nanosheets. (b) Corresponding Tafel plots obtained from the polarization curves. The Tafel slopes were ∼41 and ∼135 mV per decade for M-MoS2 and S-MoS2, respectively. (c) Polarization curves of the M-MoS2 nanosheets after 1 and 1,000 cycles of continuous operation. (d) Nyquist plots of M-MoS2 and S-MoS2.
Figure 5
Figure 5. Schematic illustrations of the evolution process of M-MoS2 from MoS3.
(a) One MoS3 cluster with S2− and S2−. (b) Combination of two MoS3 clusters with the breaking of S2−. (c) Several MoS3 cluster forming MoS2 with S2− in the centre and MoS3 with S2− at the edge. (d) Stable M-MoS2 crystal structure.
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