Electronic Supplementary Information - Infoscience · Electronic Supplementary Information Hydrogen evolution catalyzed by MoS3 and MoS2 particles ... (V dec-1) is the Tafel slope,

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Electronic Supplementary Information

Hydrogen evolution catalyzed by MoS3 and MoS2 particles

Heron Vrubel, Daniel Merki and Xile Hu*

Laboratory of Inorganic Synthesis and Catalysis, Institute of Chemical Sciences and

Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), SB-ISIC-LSCI, BCH 3305,

Lausanne, CH 1015, Switzerland

* To whom correspondence should be addressed. E-mail: [email protected]

Electronic Supplementary Material (ESI) for Energy & Environmental ScienceThis journal is © The Royal Society of Chemistry 2012

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Ohmic drop correction:

The ohmic drop correction of polarization curves has been performed according to the method

given in the literature [1-3]. The overpotential η (V) observed during an experiment is given by

equation (1):

η = a + bln j + jR (1)

where a (V) is the Tafel constant, b (V dec-1) is the Tafel slope, j (A cm-2) is the current density

and R (Ω cm2) is the total area-specific uncompensated resistance of the system, which is

assumed to be constant. The derivative of Eq. (1) with respect to current density gives Eq. (2)

from which b and R can be easily obtained by plotting dη/dj as a function of 1/j.

dηdj

=bj+ R (2)

The estimation of R allows correcting the experimental overpotential by subtracting the ohmic

drop jR according to equation (3):

ηcorr = η − jR (3)

During the calculations, the derivative dη/dj was replaced by their finite elements Δη/Δj

estimated from each pair of consecutive experimental points.

Reference

[1] D.M. Schub, M.F. Reznik, Elektrokhimiya, 21 (1985) 937

[2] N. Krstajic, S. Trasatti, Journal of Applied Electrochemistry. 28 (1998) 1291

[3] L.A. De Faria, J.F.C. Boodts, S. Trasatti, Journal of Applied Electrochemistry, 26 (1996)

1195


S3

1080 960 840 720 600 480 360 240 120 0

Binding energy (eV)

O KLL

O 1s

Mo 3p

C 1s

Mo 3d

S 2p

1080 960 840 720 600 480 360 240 120 0

S 2p

Mo 3d

C 1s

Mo 3p

O 1s

Sn 3d

Sn 3p

Binding energy (eV)

O KLL

Fig. S1. XPS survey spectra of the MoS3 particles before (top) and after (bottom) polarization.


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-0.3 -0.2 -0.1 0.0-12

-10

-8

-6

-4

-2

0

Cur

rent

den

sity

(mA/

cm2 )

Potential (V vs. RHE)

53 μg/cm2, scan 1 53 μg/cm2, scan 2 53 μg/cm2, scan 3 53 μg/cm2, scan 4 53 μg/cm2, scan 5 53 μg/cm2, scan 6

Fig. S2. Consecutive polarization curves of a freshly prepared MoS3-modified FTO electrode

(drop casting) recorded at pH = 0 (1.0 M H2SO4); scan rate: 5 mV/s.

Table S1. HER activity of drop-casted MoS3-modified FTO electrodes according to polarization measurements.

Loading (μg/cm2) log j0 (log[mA/cm2]) Tafel Slope

(mV/decade) jη=150

(mA/cm2) jη=200

(mA/cm2) 13 -4.0 60a -0.019 -0.14 27 -4.0 52b -0.056 -0.49 40 -3.7 53c -0.13 -0.79 53 -3.4 56d -0.18 -1.1 75 -2.9 61e -0.22 -1.0

a Determined at η = 140 – 196 mV; b Determined at η = 140 – 190 mV; c Determined at η = 119

– 158 mV; d Determined at η = 119 – 166 mV; e Determined at η = 112 - 158 mV.


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Table S2. HER activity of spray-casted MoS3-modified FTO electrodes according to polarization measurements.


(mV/decade) jη=150

(mA/cm2) jη=200

(mA/cm2) 18 -4.8 45a 0.040 0.47 100 -4.4 38b 0.40 2.8 200 -3.8 40c 0.73 3.6 300 -3.3 44d 1.02 3.9 400 -3.2 45e 1.03 3.9

a Determined at η = 146 - 186 mV; b Determined at η = 109 - 145 mV; c Determined at η = 110 -

134 mV; d Determined at η = 98 - 125 mV; e Determined at η = 97 - 124 mV.


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-0.3 -0.2 -0.1 0.0 0.1 0.2

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

2

Cur

rent

den

sity

(mA

/cm

2 )


a: 8 μg/cm2

b: 16 μg/cm2

c: 32 μg/cm2

d: 64 μg/cm2

e: 128 μg/cm2

baed

c

10 100-2.5

-2.0

-1.5

-1.0

-0.5

0.0

curr

ent d

ensi

ty (m

A/c

m2 )

loading (μg/cm2)

a: 150 mV overpotentialb: 200 mV overpotential

a

b

Fig. S3 (Top) Polarization curves of spray-casted MoS3-modified glassy carbon electrodes

recorded at pH = 0 (1.0 M H2SO4); scan rate: 5 mV/s. (Bottom) Loading-dependence of current

densities.


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Table S3. HER activity of spray-casted MoS3-modified glassy carbon electrodes according to polarization measurements.


(mV/decade) jη=150

(mA/cm2) jη=200

(mA/cm2) 26 -4.6 43a 0.083 0.95 77 -4.4 40b 0.26 2.5 129 -4.2 39c 0.48 4.4 180 -4.1 39d 0.49 4.1 231 -3.9 41e 0.58 3.5

a Determined at η = 139 - 175 mV; b Determined at η = 125 - 159 mV; c Determined at η = 112 -

153 mV; d Determined at η = 113 -151 mV; e Determined at η = 107 - 144 mV.

-0.3 -0.2 -0.1 0.0 0.1 0.2-40

-35

-30

-25

-20

-15

-10

-5

0

5

Cur

rent

den

sity

(mA

/cm

2 )


MoS3, no MWCNT MoS3 : MWCNT = 1 : 1 MoS3 : MWCNT = 1 : 2

Fig. S4 Polarization curves of spray-casted MoS3-modified glassy carbon electrodes, with

MWCNT as additive, recorded at pH = 0 (1.0 M H2SO4); scan rate: 5 mV/s. The loading of

MoS3 is always 130 μg/cm2.


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Fig. S5 The home-made working electrode filled with conductive graphite powder.


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-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2-7

-6

-5

-4

-3

-2

-1

0

1

MoS3 particles drop-casted on FTO (ca. 16 μg).Consecutive polarization curves in 1.0 M H2SO4 (Ti counter electrode not separated).

DM4-10-Tcell Ti

Cur

rent

den

sity

(mA

/cm

2 )


scan 1 scan 2 scan 3 scan 4 scan 5 scan 6

Fig. S6 Consecutive polarization curves of a freshly prepared MoS3-modified FTO electrode

(drop casting) recorded at pH = 0 (1.0 M H2SO4); scan rate: 5 mV/s. Ti electrode was used as a

counter electrode.


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238 236 234 232 230 228 226 224 222

Binding energy (eV)

Mo 3d3/2

231.6

Mo 3d5/2

228.55

172 170 168 166 164 162 160 158 156

Experimental data I 2p3/2

I 2p1/2

II 2p3/2

II 2p1/2

Curve fitting

Binding energy (eV)

Fig. S7 XPS spectra of the MoS3-modified electrode after five minutes of electrolysis. (Top) Mo

spectrum; (bottom) S 2p spectrum.


S11

238 236 234 232 230 228 226 224 222

Binding energy (eV)

Mo 3d5/2

228.55

Mo 3d3/2

231.6

172 170 168 166 164 162 160 158 156


I 2p1/2

II 2p3/2

II 2p1/2

Curve fitting

Binding energy (eV)

Fig. S8 XPS spectra of the MoS3-modified electrode after ten minutes of electrolysis. (Top) Mo



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237.6 235.8 234.0 232.2 230.4 228.6 226.8 225.0 223.2

Binding energy (eV)

Mo 3d5/2

228.3

Mo 3d3/2

231.4

172 170 168 166 164 162 160 158 156


I 2p1/2

II 2p3/2

II 2p1/2

Curve fitting

Binding energy (eV)

Fig. S9 XPS spectra of the MoSx species prepared by reduction of MoS3 with NaBH4. (Top) Mo



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-0.4 -0.3 -0.2 -0.1 0.0 0.1-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

Cur

rent

den

sity

(mA

/cm

2 )

Potential (V vs RHE)

MoSx - from reduction by NaBH

4

MoS3

Fig. S10 Polarization curves of FTO electrodes modified by MoSx species prepared by reduction

with NaBH4, and by MoS3 particles recorded at pH = 0 (1.0 M H2SO4); scan rate: 5 mV/s. The

electrodes were made using the same loading of catalysts and drop casting.


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240 238 236 234 232 230 228 226 224 222

Binding energy (eV)

Mo 3d5/2

228.8

Mo 3d3/2

231.9

170 168 166 164 162 160 158


I 2p1/2

II 2p3/2

II 2p1/2

Curve fitting

Binding energy (eV)


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Fig. S11 XPS spectra and electron diffraction pattern of the MoS3-350 particles. The Mo/S ratio

is 1:3.1. For S 2p region; binding energies (eV): doublet I: 2p3/2, 162.0; 2p1/2, 163.2; doublet II:

2p3/2, 163.3; 2p1/2, 164.5.


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240 238 236 234 232 230 228 226 224 222

Binding energy (eV)

Mo 3d3/2

231.8

Mo 3d5/2

228.7

S 2s

170 168 166 164 162 160 158

Experimental data S2- 2p3/2

S2- 2p1/2

Curve fitting

Binding energy (eV)


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Fig. S12 XPS spectra and electron diffraction pattern of the MoS2-650 particles. The Mo/S ratio

is 1:2.


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238 236 234 232 230 228 226 224 222

Binding Energy (eV)

Mo 3d5/2

228.55

Mo 3d3/2

231.65


S19

174 172 170 168 166 164 162 160 158 156

Binding energy (eV)

162.3

163.5

S 2p1/2

S 2p3/2

Fig. S13 (Top) TEM image (left) and electron diffraction pattern of commercial MoS2 particles.

(Middle) XPS Mo spectrum of commercial MoS2 particles. The spectrum shows a peak at lower

binding energies, which is the S 2s peak. (Bottom) XPS S spectrum of commercial MoS2

particles. The S/Mo ratio is 2.1 for MoS2 particle.


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Electronic Supplementary Information - Infoscience · Electronic Supplementary Information Hydrogen evolution catalyzed by MoS3 and MoS2 particles ... (V dec-1) is the Tafel slope,