Supporting Information

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1 Electronic Supplementary Material (ESI) for hemomm. This journal is The Royal Society of hemistry 215 Supporting Information 2H 1T Phase Transition and Hydrogen Evolution Activity of MoS 2, MoSe 2, WS 2 and WSe 2 Strongly epends on the MX 2 composition Adriano Ambrosi a, Zdeněk Sofer b and Martin Pumera a * a ivision of hemistry & iological hemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore , Singapore Fax: (65) ; pumera@ntu.edu.sg b Institute of hemical Technology, epartment of Inorganic hemistry, Technická 5, Prague 6, zech Republic 1

2 Experimental Section Materials MoS 2, WS 2, MoSe 2 and WSe 2 bulk powder (< 2 μm), and tert-butyllithium (1.7M in pentane) were obtained from Aldrich, zech Republic. Hexane was obtained from Lach-ner, zech Republic. Argon ( % purity) was obtained from SIA, zech Republic. Sulphuric acid (95-98%), N,Ndimethylformamide (MF), and platinum on graphitized carbon (2 wt% Pt on Vulcano graphitized carbon) were purchased from Sigma Aldrich, Singapore. Apparatus Voltammetric experiments were performed using a three-electrode configuration. A platinum wire served as an auxiliary electrode, while an Ag/Agl wire served as a reference electrode. All electrochemical potentials in this paper are stated versus Ag/Agl reference electrode. All voltammetric measurements were performed on a μautolab type III electrochemical analyzer (Eco hemie, The Netherlands) connected to a personal computer and controlled by General Purpose Electrochemical Systems Version 4.9 software (Eco hemie). X-ray photoelectron spectroscopy (XPS) was performed with a Phoibos 1 spectrometer and a monochromatic Mg X-ray radiation source (SPES, Germany). oth survey and high-resolution spectra for 1s were collected. Raman spectra were obtained by using a confocal micro-raman LabRam HR instrument from Horiba Scientific in backscattering geometry with a detector, a nm Ar laser and a 1x objective mounted on a Olympus optical microscope. The calibration is initially made using a silicon reference at 52 cm -1 and gives a peak position resolution of less than 1 cm -1. Scanning Transmission Electron Microscopy (STEM) images were obtained by using Jeol 21 TEM (Jeol, Japan) operating at 2 kv. Procedures Exfoliation of TMs has been carried out by suspension of 3 g of the bulk powder in 2 ml of 1.7 M t-butyllithium in pentane. The solution has been stirred for 72 h at 25 under argon atmosphere. The Li-intercalated material has then been separated by suction filtration under argon atmosphere and the intercalation compound was washed several times with hexane (dried over Na). The separated TM with intercalated Li was placed in water (1 ml) and repeatedly centrifuged (18 g). Obtained material was dried in vacuum oven at 5 for 48 hours prior the further use. Further characterization of the four TM materials in the bulk state and after exfoliation is provided in supporting information (see Figures S5, S6 and S7 for XPS analysis). Electrochemical measurements. ispersions of all materials were prepared in N,Ndimethylformamide (MF) at concentration of 5 mg/ml. 3 µl aliquot from each dispersion was deposited on a previously polished glassy carbon electrode (G) and let it dry for about 2 min at 2

3 room temperature. Polarization curves to investigate catalytic abilities towards hydrogen evolution reaction (HER) were obtained in.5 M H 2 SO 4 with scan rate of 2 mv/s. Planar resistivity measurements were conducted by depositing 1 μl of the material suspension (prepared at 1 mg/ml concentration in water) onto the interdigitated electrode (Au-IE) (width 1 μm; spacing 5 μm. The electrode was then dried under a lamp for 3 min, leaving a randomly deposited material film on the interdigitated area bridging the two Au electrode bands. Resistivity (Ohm) vs frequency (Hz) curves were obtained applying an A potential of 1 mv. Resistivity values for comparison were taken at the fixed frequency of.15 Hz. A 1 nm 2 nm 2 nm 2 nm Figure S1. Low-resolution TEM pictures of A) MoS 2, ) MoSe 2, ) WS 2 and ) WSe 2. 3

4 A E 1 2g MoS 2 -bulk MoSe 2 -bulk E 1 2g WS 2 -bulk WSe 2 -bulk Figure S2. Raman spectra of bulk A) MoS 2, ) MoSe 2, ) WS 2 and ) WSe 2. 4

5 A MoS E 1 2g E 1 2g MoSe WS WSe Figure S3. Raman spectra of exfoliated A) MoS 2, ) MoSe 2, ) WS 2 and ) WSe 2. 5

6 A Mo IV 3d W IV 4f Mo VI 3d S 2s W VI 4f MoS 2 -bulk WS 2 -bulk Mo IV 3d W IV 4f Mo VI 3d W VI 4f MoSe 2 -bulk WSe 2 -bulk Figure S4. High-resolution XPS spectra of (left) and (right) for the bulk TM materials. 6

7 -1T -2H A -1T -2H 167 MoS 2 WS T -2H MoSe 2 WSe T -2H Figure S5. High-resolution XPS spectra of (left) and (right) of exfoliated (A) MoS 2, () WS 2 () MoSe 2 and () WSe 2. 7

8 Mo 3p A Mo 4p 7 x W 4p W 4d S 2s WS2-tu-pwd-Survey-3sc MoS 2 6WS MoSe x Mo 3p Se 3p 2 MoSe2-tu-pwd-Survey-3scans PS WSe 2 8 x W 4p W 4d Se 3p asaxp S (This string can be edited in asaxps.ef/p rintfootnote.txt) 6 2 WSe2-tu-pwd-Survey 9 6 i ndi ng E nergy (ev) Figure S6. XPS wide spectra of exfoliated TMs and atomic composition. (A) MoS 2, () WS 2 () MoSe 2 and () WSe 2. 8

9 MoS 2 ulk Mo 3p WS 2 ulk A 1 MoSe 2 ulk x Mo 3p Se 3p 2 Mo 4p MoSe2 ulk-survey x WSe 2 ulk 8 7 PS 6 4 x N 1s W 4p W 4p W 4d S 2s W 4d 2 Se 3p 2 WS2 ulk-survey WSe2 u i ndi ng E nergy (ev) asaxp S (Thi s string can be edit ed in asaxps.ef/p rintfootnote.txt) S Figure S7. XPS wide spectra of bulk TM materials. (A) MoS 2, () WS 2 () MoSe 2 and () WSe 2. 9

10 A 3/2 5/2 1/2 3/2 MoS 2 -bulk MoSe 2 -bulk /2 5/2 1/2 3/2 WS 2 -bulk WSe 2 -bulk Figure S8. High-resolution XPS spectra of (left) and (right) for the bulk TM materials. (A) MoS 2, () MoSe 2 () WS 2 and () WSe 2. 1

11 A Resistivity (Ohm x 1 6 ) Resistivity (Ohm x 1 6 ) MoSe 2 WS 2 MoS 2 WSe 2 MoSe 2 WS 2 MoS 2 WSe 2 Figure S9. Planar resistivity of MoS 2, MoSe 2, WS 2 and WSe 2 (1μg) measured with an Au-IE electrode (Width 1 μm, spacing 5 μm) applying an A potential of 1 mv. A) Resistivity values taken at the frequency of.15 Hz. Picture of a section of the Au-IE electrode before () and after () deposition of one TM material. Scale bar corresponds to 1 μm. 11

12 Overpotential (V) 1.9 b = 137 mv/dec b > 24 mv/dec.8.7 G WSe b = 85 mv/dec b = 99 mv/dec.3 b = 82 mv/dec MoSe.2 2 MoS 2 WS 2.1 b 3 mv/dec Pt log i (ma/cm 2 ) Figure S1. Tafel plots and corresponding slopes relative to the polarization curves in Figure 4. 12