Mater. Res. Lett. 1 (2013) 1–9
Supporting Information
Optimizing Hybridization of 1T and 2H Phases in MoS2 Monolayers to Improve
Capacitances of Supercapacitors
Lianfu Jianga,b[+], Shengli Zhangb[+], Sergei A. Kulinichc, Xiufeng Songb,
Junwu Zhud, Xin Wangd,Haibo Zenga,b*
Fig. S1. Partial s, p, and d densities of states (DOS) for 1T (b) and 2H (a) MoS2, where all Fermi
energies are set at zero.
Computational Method：The density functional theory (DFT) calculations were performed using the
Vienna ab initio simulation package (VASP). The core-valence interaction was described by the
projector-augmented-wave (PAW) method. The generalized gradient approximation of Perdew-BurkeErnzerhof (GGA-PBE) was used to account for the exchange-correlation functional. The plane-wave
energy cutoff was set to 400 eV. A vacuum region of 20 Å was employed for all the systems to avoid
interaction of periodic images. The force convergence criterion was set to 0.01 eV/Å for optimization.
In order to analyze the stabilities of the 1T, 2H and 2H+1T MoS 2 NSs, we calcualted system energy
with a large supercell9×9 with same atom numbers for the 1T, 2H and 2H+1T MoS2 models.
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Figure S2. (a) SEM images of pristine MoS2 crystal, with inset showing a higher-magnification image
of layered structure (scale bar in the inset is 1 µm). (b) LiXMoS2 after intercalation with Li cations
followed by exposure in the air for 3 days. (c) SEM image shows wrinkled and multiporous freezedried monolayer MoS2 NSs. (d) Cross-sectional SEM image of ultrathin MoS2 NSs, the film was
prepared by filtering a diluted suspension through a mixed cellulose ester membrane with 0.22 µmsized pores .
Figure S3. (a-p) AFM images of typical monolayer-MoS2 NSs deposited on a mica substrate. The
height distribution shows an average thickness around 0.8 nm (based on 100 NSs). 95% of the NSs
were found to be monolayers, confirming that monolayered MoS2 material was successfully obtained
(insets are corresponding height distributions of the NSs in the AFM images).
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Figure S4. (a-h) AFM images of few-layered MoS2 NSs deposited on Si/SiO2 substrates. Based on 100
NSs measured, it was found that 90% of few-layered NS have more than two layers, with their
thickness distribution being between 1 nm and 40 nm (insets are corresponding height distributions of
the NSs in the AFM images).
Figure S5. (a) Low-magnification SEM image of as-exfoliated wrinkled and multiporous freeze-dried
ultrathin MoS2 NSs. (b) Low-magnification TEM image of randomly-stacked monolayer-MoS2 NSs. The
insert is a corresponding SAED pattern. (c,d) HRTEM images of strongly-disordered (inside the basal
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plane) MoS2 NSs. Only short-range ordering of nano-domains is observed in certain regions, because
during the Li-intercalation process the phase transformation from 2H to 1T occurred, which distorted
and strained the crystal structure.
Figure S6. XRD patterns of few-layer-MoS2 NSs (red) and pristine 2H-hybridized MoS2 powder
(black).
Figure S7. Table 1. XPS peak positions measured for as-exfoliated MoS2 NSs, after drying at 60 oC for
12 h, and those of pristine 2H-hybridized MoS2 powder.
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Figure S8. (a) XPS survey spectrum of monolayer MoS2 NSs after drying at 60 oC for 12 h. (b)
Narrow-scan XPS oxygen spectrum showing the binding energies of oxygen (O1s) located at 530.0 eV
and 532.0 eV and attributed to Mo(IV)−O in MoO2 and the adsorbed water on the surface of MoS2 NSs.
The characteristic peaks observed around 169 eV arise from the microscale oxidized states of sulfur
atoms. (c-d) Narrow-scan XPS spectra showing Mo 3d, S 2s, and S 2p core level peaks of MoS2 NSs
dried at 60 oC for 12 h and pristine MoS2 powder. The 2H and 1T phases are represented by pink and
green lines, respectively. The results indicate that the MoS2 NSs obtained via Li intercalation consist of
two distinct phases and microscale oxygen-incorporated in the NSs. During annealing, the 2H phase
can be restored, which can be followed by Raman and XPS measurements.[1-3]
Figure S9. Table 2. Content of 1T phase in annealed monolayers as a function of annealing
temperature.
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Figure S10. (a) CV curves of electrode based on 2H-hybridized-MoS2 monolayers (1T-2H monolayers
anealled at 300 oC for 2h in Ar/H2 ) at different scan rates ranging from 5 to 75 mV s-1. (b)
Galvanostatic charge/discharge voltage profiles of the same electrode at various current densities
ranging from 0.5 A g-1 to 5 A g-1. (c) Specific capacitance of the same electrode as a function of
current density. (d) Cycle life of the same electrode at current density of 1 A g-1 in 6 M KOH electrolyte.
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Figure S11. (a) CV curves of electrode based on few-layer-MoS2 NSs at different scan rates ranging
from 5 to 75 mV s-1. (b) Galvanostatic charge/discharge voltage profiles of the electrode at various
current densities ranging from 0.5 A g-1 to 8 A g-1. (c) Specific capacitance of the electrode based on
few-layer NSs as a function of current density. (d) Cycle life of the electrode based on few-layer-MoS2
NSs at a current density of 1 A g-1 in 6 M KOH electrolyte.
Figure S12. Electrochemical characterization of the electrode based on pristine MoS2 as reference. (a)
CV curves of the electrode at different scan rates ranging from 5 to 80 mV s-1. (b) Discharge voltage
profiles at various current densities ranging from 0.5 to 5 A g-1. (c) Calculated capacitance of the
electrode as a function of current density. (d) Capacitance cycling performance of the electrode at
acurrent density of 1 A g-1 in 6 M KOH electrolyte.
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Figure S13. Nitrogen adsorption and desorption isotherms of monolayer MoS2 NSs and pristine MoS2.
The specific surface areas of monolayer MoS2 NSs and pristine MoS2 are calculated as 63.2 m2•g-1 and
5.107 m2•g-1, respectively. The insert shows a uniform pore size distribution in the monolayer MoS2
NSs within the range of 3-8 nm as determined by the BJH method.
Figure S14. EIS of pristine MoS2, few-layer MoS2 and monolayer-MoS2 NSs (the inset is the enlarged
low-frequency region). The Nyquist plots of the EIS for pristine MoS 2, few-layer MoS2 and monolayer
MoS2 NSs, according to analysis of Nyquist plots: there is nearly no Nyquist‘s arc in the high-frequency
region and the short Warburg region on the Nyquist plots, which could also explain the hybridized
monolayer-MoS2 NSs have a high intrinsic conductivity. In the low-frequency region the Nyquist plot
shows that the ion diffusion in the electrolyte is more facilitated compared with other two
electrodes.[4-6]
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Characterization. The samples were characterized in a Bruker D8 Advance diffractometer (Cu Kα
radiation, λ=1.5418 Ȧ , 0.1oper second.). Field-emission scanning electron microscope (FESEM)
images were obtained on a field emission scanning electron microscopy, Hitach, SU8010).
Transmission electron microscopy (TEM) images and corresponding SAED were achieved on a Tecnai
G2 F30 S-TWIN operated at an acceleration voltage of 300 kV in TEM mode. HAADF STEM imaging
was performed using Titan G2 80-200 w/ ChemiSTEM, FEI TEM/STEM with double spherical aberration
(Cs) correctors (CEOS GmbH, Heidelberg, Germany), the acceleration voltage was set to 120 kV which
is the lowest voltage with effective Cs correctors in the system. Nitrogen sorption isotherms and BET
surface area were measured at 77 K with a quantachrome NOVA (USA) surface area and porosimetry
analyzer at 77 K. X-ray photoelectron spectroscopic (XPS) measurements were performed on a PHI
QuanteraⅡspectrometer. All spectra were taken using a Al Kα microfocused monohromatized source
(1486.6 eV) with a resolution of 0.6 eV and a 400 μm spot size. The MoS 2 samples were measured on
Pt foil, and Pt4f7/2 was taken as reference at 70.98 eV. AFM data were obtained in Bruker Multimode 8
Atomic Force Microscope in scanasyst-air mode with standard cantilevers with spring constant of 0.4
N/m, back side 100 nm Al coating and tip curvature <10 nm. The sample was deposited on a micro
substrate and dried overnight at room temperature. Raman spectra were measured with an InVia
Raman microscope (Renishaw) at excitation laser wavelength of 532 nm.
Electrochemical measurements. For electrochemical measurements, the working electrodes were
fabricated by mixing the samples, acetylene black and a polytetrafluorene-ethylene (PTFE) binder in a
mass ratio of 80 : 15: 5. A small amount of DI-water was added and the mixture was stirred to
produce a homogeneous paste. The slurry was filled into the nickel foam substrate (1 cm×1 cm, the
Ni foam is treated with a 3 M HCl solution to remove the possible oxide layer on the surface) followed
by drying at 60 OC for 12 h and then press under the pressure of 10 MPa to make electrodes. The
average mass loadings of the active material are 8.5 mg cm-2 on the current collector.
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