electronic supplementary information - edge-exposed mos2

Electronic supplementary Information

Edge-exposed MoS2 nano-assembled structures as an efficient electrocatalyst for hydrogen evolution reaction

Dong Young Chunga,b, Seung-Keun Parkc, Young-Hoon Chunge, Seung-Ho Yua,b, Dong-Hee Lime, Namgee Junge, Hyung Chul Hame, Hee-Young Parke, Yuanzhe Piaoc,d, Sung Jong Yooe* and Yung-Eun Sunga,b*

Electronic Supplementary Material (ESI) for NanoscaleThis journal is © The Royal Society of Chemistry 2013

SI1. TEM images of spherical MoS2

Figure S1. Low magnified HR TEM of MoS2 sphere.


SI2. SEM images and EDS results.

Figure S2. SEM images and EDS results of (a) MoS2 nanosphere and (b) MoS2 nanosheet


SI3. Raman images.

Figure S3. Raman images and EDS results of (a) bulk MoS2, (b) MoS2 nanosphere and (c)

MoS2 nanosheet


SI4. XANES analysis

Figure S4 First derivatives of XANES results to confirm the oxidation state of Mo.

From the derivatives on the XANES spectra, there are no significant changes in the onset and

edge of the normalized absorbance profiles, which means that the oxidation states of each Mo

is similar. The oxidation states of sphere and sheet samples could be estimated 4+ due to the

oxidation state of Mo on bulk MoS2 is 4+.


SI5. EXAFS analysis reuslts.

Table S1. EXAFS fitting parameters.

Mo-S interatomic distance (Å) /

Debye-Waller factor (σ2 / Å2)

Coordination number (N)

Mo-Mo interatomic distance(Å) / Debye-Waller factor (σ2 / Å2)

Coordination number (N)

R factor

(%)

Bulk 2.4249 ± 0.0114

/ 0.0032

5.98 3.1614 ± 0.0121

/ 0.0030

5.97 0.059

Nano-assembled sphere

2.4004 ± 0.0131

/ 0.0025

3.74 3.1589 ± 0.0089

/ 0.0104

3.35 0.020

Nanosheet

2.4033 ± 0.0102

/ 0.0022

4.43 3.1644 ± 0.0145

/ 0.0039

4.39 0.015


SI6. Coordination number calculation for EXAFS analysis.

Figure S5. Quantification of nearest neighbor atoms with Mo K edge absorption (a) Mo edge

and (b) S edge. The large (gray), and the small (yellow) spheres represent Mo and,

respectively. Solid red line indicates the absorption Mo atom.


SI7. Effect of Heat treatment

Figure S6. HER activities of synthesized MoS2 sample before/after heat trearment

As reported that the heat treatment affects the edge site in REF is important issue, however

we expect that edge deformation through heat treatment is minor effect in our cases. The

removal of impurity enhanced the activity of our samples. Residual organic molecules in the

sources of sulfur may block the surface which can deactivate the HER activity.


SI8. DFT analysis.

Spin-polarized density functional theory calculations were performed using the Vienna ab

initio Simulation Package (VASP)1-4 with the projector-augmented wave (PAW)5, 6 method.

Electron exchange-correlation functionals were represented with the generalized gradient

approximation (GGA), and the model of Perdew, Burke and Ernzerhof (PBE)7 was used for

the nonlocal corrections. A kinetic energy cutoff of 300 eV was used with a plane-wave basis

set. MoS2 nanoparticle structures were derived from a bulk MoS2 (space group of R3m with

the lattice constant of 3.16 Å) determined by Schonfeld et al.8 An orthorhombic supercell of

22 × 22 × 15 Å was used for MoS2 nanoparticles with a vacuum space of 12.0 Å. As shown

in Figure 5 in manuscript, two types of MoS2 nanoparticles were considered: S-terminated

and Mo-terminated. The integration of the Brillouin zone was carried out for the Γ-point only.

In order to mimic the effect of bulk MoS2 without the edge effect, a trigonal supercell of 6.33

× 6.33 × 15.00 Å with periodic boundary conditions was used with a vacuum space of 11.9 Å.

The Brillouin zone integration of the trigonal structure was conducted using a 8×8×1

Monkhorst-Pack grid9 with the Γ-point included and first-order Methfessel-Paxton smearing10

with a width of 0.1 eV. All atoms were fully relaxed and optimized until total energy change

upon two steps of the electronic self-consistent loop less than 10-4 eV.

The adsorption energy (Eads) of atomic hydrogen is defined as Eads = EMoS2+H – EMoS2 – EH2 / 2,

where EMoS2+H, EMoS2, and EH2 are the total energies of MoS2 systems with adsorbed H, bare

MoS2 systems, and a gas phase H2 molecule. A negative adsorption energy indicates that

adsorption is exothermic (stable) with respect to the free gas phase hydrogen.


Figure S7. Optimized structures of S edge terminated MoS2 nanoparticles wuth adsorbed H

and adsorption energies depending on adsorption sites

(1) Kresse, G.; Hafner, J., Ab initio molecular dynamics for liquid metals. Physical

Review B 1993, 47, 558-561.

(2) Kresse, G.; Hafner, J., Ab initio molecular-dynamics simulation of the liquid-metal

amorphous-semiconductor transition in germanium. Physical Review B 1994, 49, 14251-

14269.

(3) Kresse, G.; Furthmüller, J., Efficient iterative schemes for ab initio total-energy

calculations using a plane-wave basis set. Physical Review B 1996, 54, 11169-11186.

(4) Kresse, G.; Furthmüller, J., Efficiency of ab-initio total energy calculations for metals

and semiconductors using a plane-wave basis set. Computational Materials Science 1996, 6,

15-50.

(5) Blöchl, P. E., Projector augmented-wave method. Physical Review B 1994, 50,


17953-17979.

(6) Kresse, G.; Joubert, D., From ultrasoft pseudopotentials to the projector augmented-

wave method. Physical Review B 1999, 59, 1758-1775.

(7) Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized gradient approximation made

simple. Physical Review Letters 1996, 77, 3865-3868.

(8) Schonfeld, B.; Huang, J. J.; Moss, S. C., ANISOTROPIC MEAN-SQUARE

DISPLACEMENTS (MSD) IN SINGLE-CRYSTALS OF 2H-MOS2 AND 3R-MOS2. Acta

Crystallographica Section B-Structural Science 1983, 39, 404-407.

(9) Monkhorst, H. J.; Pack, J. D., Special points for Brillouin-zone integrations. Physical

Review B 1976, 13, 5188-5192.

(10) Methfessel, M.; Paxton, A. T., High-precision sampling for Brillouin-zone integration

in metals. Physical Review B 1989, 40, 3616-3621.


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