supporting information for · working electrode, saturation mercury reference electrode (sce) and...

S1

Supporting information for Manuscript ID: EE-ART-12-2012-024343

Visible Light Driven Overall Water Splitting with Cocatalyst/BiVO4 Photoanode

Assisted with the Minimized Bias

Chunmei Ding, Jingying Shi, Donge Wang, Zhijun Wang, Nan Wang, Guiji Liu, Fengqiang Xiong, Can Li* 5

State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023,

China

Dalian National Laboratory for Clean Energy, Dalian, 116023, China

University of Chinese Academy of Sciences, China

10

Experimental details---------------------------------------------------------------------------------------Page S2-6

Fig. S1 Cyclic voltammetric scan of 0.2 M sodium borate solution (pH 9) containing Co2+

--------------S6

Fig. S2 I-t curves for electrodeposition process of BiVO4 and CoBi -----------------------------------------S6

Fig. S3 (a) XRD and (b) UV-vis of BiVO4 and CoBi/BiVO4 electrodes--------------------------------------S7 15

Fig. S4 (a) SEM images of the electrodeposited film before (a) and after calcination (b, c)---------------S8

Fig. S5 A scheme of the setup for the PEC water spliting reaction and gas evolution determination-----S9

Fig. S6 SEM images of CoBi/BiVO4 electrode and the EDX element mapping result--------------------S10

Fig. S7 (a) XRD pattern, (b) SEM image and (c) EDX of CoBi film on FTO substrate------------------S11

Fig. S8 LSV of (a) BiVO4 and CoBi/BiVO4 photoanodes under AM 1.5G illumination without a shuttle 20

and (b) CoBi film under choped light irradiation---------------------------------------------------------------S12

Fig. S9 LSV of bare BiVO4 photoanode under frontside and backside irradiation------------------------S13

Fig. S10 LSV of CoBi/BiVO4 photoanode with different deposition times of CoBi-----------------------S14

Fig. S11 Comparison of CoBi/BiVO4 and CoPi/BiVO4 system ----------------------------------------------S15

Fig. S12 LSV of CoBi/BiVO4 photoanode in a two-electrode system vs. Pt--------------------------------S16 25

Fig. S13 Time courses of gas evolution for CoBi/BiVO4 electrode under 0.9 V, 0.2 V and the control

experiments of bare BiVO4, CoBi/BiVO4 in Na2SO4, CoBi/BiVO4 in dark condition---------------------S17

Fig. S14 I-t curves and ABPE of CoBi/BiVO4 under different biases vs. Pt--------------------------------S18

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical PhysicsThis journal is © The Owner Societies 2013

S2

Experimental details

1. Materials

All chemicals were analytical grade and were used as purchased without further purification. Solutions

were prepared using high purity water (Millipore Milli-Q purification system, resistivity > 18 MΩ·cm).

The FTO (fluorine-doped tin oxide) conductive glass was purchased from Nippon Sheet Glass Company 5

(Japan) and was ultrasonic cleaned with acetone, ethanol and deionized water for 20 min each in

sequence prior to use.

2. Fabrication of BiVO4 and CoBi/BiVO4 electrodes

BiVO4 electrodes were prepared by electrodeposition followed by an annealing procedure similar with

that reported by Seabold et al.1 Typically, 3.5 g VOSO4.xH2O (≥ 98.5%, Shanghai Chemical) and 2.4 g 10

Bi(NO3)3.6H2O (≥ 99%, Sinopharm Chemical) were dissolved in 425 mL 0.75 M HNO3 solution. The

pH value was raised to 5.1 with 102.5 g sodium acetate (≥ 99%, Tianjin Kemiou Chemical) and then

adjusted to 4.7 with concentrated HNO3 (65% ~ 68%, Tianjin Kemiou Chemical) and H2O. A CH

Instruments 760D potentiostat was used for the electrodeposition and all subsequent electrochemical

studies. The electrodeposition was carried out potentiostatically at 1.9 V vs. Ag/AgCl for 40 min at 15

70 °C without stirring in a three-electrode cell with FTO working electrode, Ag/AgCl (saturated KCl)

reference electrode and Pt counter electrode (2 cm × 4 cm). The solution seemes to be slightly turbid

after electrodeposition at 70 °C. The adhension of the deposited film to FTO is better when the solution

is heated and the solution turned completely turbid if the temprature is higher than 70 °C. The

as-deposited films were rinsed and then annealed at 500 °C for 1 h in air with a ramping rate of 2 °C 20


S3

min-1

. Then it was immerged in 1 M KOH solution under stirring for 20 min to remove the V2O5

impurity.

BiVO4 electrodes were loaded with CoBi cocatalyst via electrodeposition method carried out in 0.2 M

sodium borate buffer solution (pH 9) containing 30 μM Co2+

. Fresh solution was prepared for each

experiment by dissolving Co(NO3)2.6H2O (≥ 99%, Sinopharm Chemical) to 0.2 M sodium borate 5

solution (H3BO3 and Na2B4O7.10H2O, ≥99.5%, Sinopharm Chemical). The sodium borate buffer was

prepared by mixing 800 mL 0.05 M Na2B4O7 solution with 200 mL 0.2 M H3BO3 solution. A small

amount of precipitate was observed following the dissolution of Co2+

source. Prior to use, this solution

was passing through a 0.45 μm syringe filter to remove the microprecipitates. From the cyclic

voltammetric scans of the solution, Co2+

was oxidized at 0.59 V vs. SCE (Fig. S1). So the deposition of 10

CoBi was carried out in a three-electrode cell at 0.59 V with BiVO4 working electrode, saturation

mercury reference electrode (SCE) and Pt counter electrode (2 cm × 4 cm). The loading amount of

CoBi was controled by the deposition time and the electric charge passed per geometric area, the

deposition amount of CoBi on BiVO4 was 10 μC cm-2

(the corresponding depostion time was around 5 s

and loading amount of Co was 0.01 wt % determined by ICP) unless otherwise stated. For comparison, 15

CoBi were electrodeposited on FTO substrate via the same procedure.

The I-t profile for the electrodeposition of BiVO4 and CoBi were given in Fig. S2.

For comparison, CoPi cocatalyst was loaded on BiVO4 electrode via PEC deposition as described

previously which was reported to be the most efficient loading method for CoPi cocatalyst2,3

. The

loading amount of CoPi was also optimized.. 20


S4

3. Characterizations of the electrodes

The prepared samples were characterized by X-ray powder diffraction (XRD) on a Rigaku

D/Max-2500/PC powder diffractometer using Cu Kα radiation (operating voltage: 40 kV, operating

current: 200 mA, scan rate: 5° min-1

). The UV−visible diffuse reflectance spectra (Fig. S3c) were

recorded on a UV-visible spectrophotometer (JASCO V-550) and calibrated by Kubelka-Munk method. 5

The morphologies and energy dispersive X-ray (EDX) of the electrodes were examined by a Quanta 200

FEG scanning electron microscope (SEM) equipped with an energy dispersive spectrometer

(accelerating voltage of 20 kV). X-ray photoelectron spectroscopy (XPS) measurements were performed

using a VG ESCALAB MK2 spectrometer with monochromatized Al Kα excitation (12.0 kV, 240 W).

4. PEC measurements 10

The photocurrents, EIS (Electrochemical Impedance Spectroscopy), IPCE (Incident Photon-to-current

Efficiency), MS (Mott-Schottky) measurement were performed in a three-electrode setup with Pt

counter electrode (2 cm × 3 cm) and SCE reference electrode with a scanning rate of 20 mV s-1

. For

photocurrent measurement, the light source was a 300 W Xe lamp with an optical filter (Kenko, L-42;

λ > 420 nm) unless otherwise stated, the light intensity at the surface of the electrode is 400 mW cm-2

. 15

Prior to measurement, the areas of electrodes were fixed by insulating cement.

The EIS was recorded on an IM6ex electrochemical workstation (Germany, Zahner Company) from

100 mHz to 10 kHz at 0.4 V vs. SCE using a 140 W Xe lamp with an optical filter (λ > 420 nm) as light

source.

The MS plots were measured on a PARSTAT2273 electrochemical workstation (Princeton Applied 20

Research) in 0.2 M sodium borate (pH 9) electrolyte.


S5

IPCE was measured using a monochromator (CROWNTECH QEM24-D 1/4 m Double) and the light

intensity of each wavelength was measured using a hand-held optical power meter (Newport 70260,

USA). IPCE values were calculated according to equation (1)4:

A

i

N j( )/Felectron fluxIPCE( )

photon flux P ( )/E( )

(1)

where j(λ) is the measured photocurrent (A), Pi(λ) is the incident light intensity (W) for each wavelength, 5

NA is the Avogadro constant, F is the Faraday constant and E(λ) is the photon energy calculated by hc/λ.

5. Measurements of H2 and O2 evolution and Applied Bias Photon-to-current Efficiency

PEC water splitting reactions were carried out in a two-electrode cell connected to a closed gas

circulation and evacuation system (Fig. S5). Typically, BiVO4 (2 cm × 3 cm) working electrode and Pt

counter electrode (3 cm × 3.5 cm) with a distance of 2 cm were immerged in 85 mL electrolyte. The 10

system was thoroughly degassed and then irradiated by a 300 W Xe (λ > 420 nm) from the backside of

BiVO4 electrode. The electrochemical cell was maintained at 15 ± 2 °C by a cooling water bath during

the reaction. Evolved O2 and H2 were analyzed by an online gas chromatograph with thermal

conductivity detector (Agilent GC 7890, 5A zeolite column and Ar carrier gas).

The measurement of ABPE (Applied Bias Photon-to-current Efficiency) was performed in the same 15

two-electrode system as mentioned above under simulated AM 1.5G solar light irradiation (100 mW

cm-2

, Newport Sol3A Class AAA Solar simulator). The ABPE value was calculated according to the

equation (2)4,5

:

100%

)(mW/cm P

)V-V (1.23)(mA/cm jABPE

AM1.5G

2

b2

i (2)


S6

in which j (mA cm-2

) is the measured photocurrent density, Vb is the bias between the working

electrode and counter electrode and Pi is the incident light intensity (100 mW cm-2

).

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

C

urr

en

t/m

A

Potential vs SCE/V

0.2 0.4 0.6 0.8-0.05

0.00

0.05

0.10

Cu

rre

nt/

mA

Potential vs SCE/V

0.59 V vs. SCE

Fig. S1 Cyclic voltammetric scan of 0.2 M sodium borate solution at pH 9 containing 30 μM Co2+

in a

three-electrode cell with a FTO working electrode, saturation mercury electrode (SCE) reference 5

electrode and Pt counter electrode.

0 5 10 15 20 25 30 35 400.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 5 61.44

1.48

1.52

1.56

Curr

ent density/(

mA

cm

-2)

Time/min

(a) (b)

Curr

ent density/(A

cm

-2)

Time/s

Fig. S2 The current-time profile for electrodeposition process of (a) BiVO4 and (b)CoBi


S7

350 400 450 500 550 600 650 7000.0

0.5

1.0

1.5

2.0

2.5

(a)In

ten

sity/(

a.u

.)

10 20 30 40 50 60

2 theta/o

(b)

(c)

F(R

)

Wavelength/nm

BiVO4

CoBi /BiVO

4

Fig. S3 (a) The XRD pattern of BiVO4 electrode on FTO substrate (the peaks noted by * are FTO

signals), (b) standard monoclinic BiVO4 XRD pattern (PDF# 14-0688), and (c) UV-visible diffusion

spectra of BiVO4 and CoBi/BiVO4 electrodes.


S8

500 nm

(a)

500 nm

(b)

100 nm

(c)

Fig. S4 SEM images of the electrodeposited film before (a) and after calcination (b, c)


S9

Fig. S5 A scheme of the setup for the PEC water spliting reaction and gas evolution determination


S10

Co K

B KV K

Bi M

100 nm

Fig. S6. SEM images of CoBi/BiVO4 electrode and the corresponding EDX maps investigated in the

Bi M, V K, Co K, B K transition.


S11

amorphous CoBi film

Inte

nsity/(

a.u

.)

(a)

10 20 30 40 50 60 70

2 theta/o

SnO2 PDF# 46-1088

100 nm

(b)

Fig. S7 (a) XRD pattern, (b) SEM image and EDX histogram of CoBi film electrodeposited on FTO

substrate 5


S12

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6-0.1

0.0

0.1

0.2

0.3

0.4

(a)

-0.23 V

Cu

rre

nt

de

nsity/(

mA

cm

-2)

Potential vs. SCE/V

1 CoBi/BiVO

4-borate-light

2 BiVO4-borate-light

3 CoBi/BiVO

4-borate-dark

4 BiVO4-borate-dark

-0.55 V 3, 4

1

2

Cu

rre

nt

de

nsity/

(mA

cm

-2)

Potential vs. SCE/ V

(b)

Fig. S8 (a) LSV scans of BiVO4 and CoBi/BiVO4 photoanodes under Am 1.5G illumination without a

shuttle and (b) LSV scan of CoBi film under 300 W Xe lamp (λ > 420 nm) chopped light irradiation;

Scanning rate: 20 mV s-1

; Electrolyte: 0.2 M sodium borate (buffered at pH 9)

5


S13

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6-0.2

0.0

0.2

0.4

0.6

0.8

1.0

2

off

Cu

rre

nt

de

nsity/(

mA

cm

-2)

Potential vs. SCE

1 BiVO4-backside illumination

2 BiVO4-frontside illumination

on

1

Fig. S9 (a) LSV scans of bare BiVO4 photoanode under frontside and backside irradiation. Electrolyte:

0.2 M sodium borate electrolyte (pH 9); Light source: 300 W Xe lamp (λ > 420 nm); (b) A scheme of the

setup for PEC water splitting reactions.

5


S14

-0.2 0.0 0.2 0.4 0.6

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 10 100 120 140 160 180 200

1.0

1.2

1.4

1.6

1.8

g

fedc

Curr

en

t d

en

sity/(

mA

/cm

2)

Cu

rre

nt

de

nsity/(

mA

cm

-2)

Potential vs. SCE/V

a 4 s

b 8 s

c 2 s

d 15 s

e 50 s

f 200 s

g 0 s

(a)

offon

ba

(b)

Deposition time of CoBi/s

0.43 V vs. SCE

Fig. S10 (a) LSV scans of CoBi/BiVO4 photoanode with different deposition times of CoBi under

chopped light illumination and (b) the comparison of the photocurrent density at 0.43 V vs. SCE with

different deposition time of CoBi. Electrolyte: 0.2 M sodium borate electrolyte (pH 9); Light source: 300

W Xe lamp (λ > 420 nm). 5

10


S15

0.2 0.4 0.6 0.8 1.0 1.2 1.4

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

3

Curr

ent density/(

mA

/cm

2)

Potential vs. RHE/V

CoBi/BiVO

4-borate

BiVO4-borate

CoPi/BiVO4-phosphate

BiVO4-phosphate

(a)offon

1

4

2

3

1

4

2

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

(b)

4

2

3

Curr

ent density/(

mA

/cm

2)

Time/h

1 CoBi/BiVO

4-borate

2 BiVO4-borate

3 CoPi/BiVO4-phosphate

4 BiVO4-phosphate

1

Fig. S11 (a) Linear sweep voltammetric scans and (b) amperometric i-t curves at 1.175 V vs. RHE of

bare BiVO4 and CoPi/BiVO4 electrodes in 0.2 M sodium phosphate (buffered at pH 7), and bare BiVO4

and CoBi/BiVO4 electrodes in 0.2 M sodium borate (buffered at pH 9) electrolyte; Light source: 300 W

Xe lamp (λ > 420 nm); Scanning rate: 20 mV/s. 5


S16

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

dark

Curr

ent density/(

mA

cm

-2)

Voltage vs. Pt/V

light

CoBi/BiVO

4

Fig. S12 LSV scans of CoBi/BiVO4 photoanode in a two-electrode system with Pt as counter electrode

and reference electrode. Electrolyte: 0.2 M sodium borate electrolyte (pH 9); Light source: 300 W Xe

lamp (λ > 420 nm).


S17

0 1 2 3 40

1

2

3

4

0 1 2 3 40

1

2

3

4

5

0 1 2 3 40

2

4

6

8

10

0 1 2 3 40

50

100

150

0 1 2 3 40.0

0.5

1.0Time/h

CoBi/BiVO

4 0.2 V vs. Pt

e/2

H2

O2

Gas e

volu

tion/

mol

(a)bare BiVO

4 0.6 V vs. Pt

e/2

H2

O2

Time/h

Gas e

volu

tion/

mol

(c)

(d)

(e)

(c)

(b)

CoBi/BiVO

4 0.6 V vs. Pt

Na2SO

4 e/2

H2

O2

Time/h

Gas e

volu

tion/

mol

Time/h

e/2

H2

O2

CoBi/BiVO

4 0.9 V vs. Pt

Gas e

volu

tion/

mol CoB

i/BiVO

4 1 V vs. Pt

dark e/2

H2

O2

Time/h

Gas e

volu

tion/

mol

Fig. S13 Time courses of gas evolution (square dots: H2, triangular dots: O2) and the theoretical H2

evolution amounts e/2 (solid lines) with CoBi/BiVO4 electrode under (a) 0.2 V, (b) 0.9 V vs. Pt in 0.2 M

sodium borate (pH 9) and the control experiments of (c) CoBi/BiVO4 in 0.2 M Na2SO4 (pH 9), (d) bare

BiVO4 and (e) CoBi/BiVO4 in dark condition under a bias of 1 V in 0.2 M sodium borate (pH 9). Light 5

source: 300 W Xe lamp (λ > 420 nm).


S18

0 5 10 15 20 25 30

0.2

0.4

0.6

0.8

1.0

1.2

0.3 0.4 0.5 0.60.1

0.2

0.3

0.4

0.5

0.6

0.7

0.3 V

0.4 V

0.6 V

C

urr

en

t d

en

sity

/(m

A c

m-2)

Time/min

(a) (b)

AB

PE

/%Voltage/V

1min

30 min

ABPE

Fig. S14 Amperometric i-t curves of CoBi/BiVO4 photoanode under different biases vs. Pt counter

electrode in 0.2 M sodium borate electrolyte (pH 9) and the corresponding ABPE (Applied Bias

Photon-to-current Efficiency) calculated by the average photocurrent during 1 min and 30 min

illumination. Light source: AM 1.5G sun light simulater. 5

References for ESI

1 Seabold, J. A. and Choi, K., J. Am. Chem. Soc., 2012, 134, 2186-2192.

2 Zhong, D. K., Choi, S. and Gamelin, D. R., J. Am. Chem. Soc., 2011, 133, 18370-18377. 10

3 Zhong, D. K., Cornuz, M., Sivula, K., Gr A Tzel, M. and Gamelin, D. R., Energy Environ. Sci., 2011, 4, 1759-1764.

4 Chen, Z. B., Jaramillo, T. F., Deutsch, T. G., Kleiman-Shwarsctein, A., Forman, A. J., Gaillard, N., Garland, R., Takanabe,

K., Heske, C., Sunkara, M. and Others, J. Mater. Res., 2010, 25, 3-16.

5 Jia, Q., Iwashina, K. and Kudo, A., PNAS, 2012, 109, 11564-11569.

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