Boosting Charge Separation and Transfer by Plasmon-Enhanced

Subscriber access provided by University of Chicago Library

Boosting charge separation and transfer by plasmon enhanced MoS2/BiVO4 p-n heterojunction composite for efficient photoelectrochemical water splitting Qingguang Pan, Chi Zhang, Yunjie Xiong, Qixi Mi, Dongdong Li, Liangliang Zou, Qinghong Huang, Zhiqing Zou, and Hui Yang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00170 • Publication Date (Web): 13 Apr 2018 Downloaded from http://pubs.acs.org on April 15, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

1 2 3 4 5

Boosting charge separation and transfer by plasmon enhanced MoS2/BiVO4 p-n heterojunction composite for efficient photoelectrochemical water splitting Qingguang Pana,b,c, Chi Zhanga, Yunjie Xionga,b,c, Qixi Mib, Dongdong Lia, Liangliang Zoua, Qinghong Huanga, Zhiqing Zoua, Hui Yanga,b*

6 7

a

8

Zhangjiang Hi-Tech Park, PuDong, Shanghai 201210, China.

9

b

School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.

10

c

University of Chinese Academy of Sciences, Beijing 100039, China.

11

*Corresponding author. E-mail: [email protected]

12

ABSTRACT

13

The poor separation and significant recombination of electron-hole pairs and slow transfer mobility of

14

charge carriers limit the performance of BiVO4 for photoelectrochemical (PEC) water splitting. To

15

ameliorate the above problems, a novel integrated Ag-embedded MoS2/BiVO4 p-n heterojunction ternary

16

composite electrode is fabricated and applied. Surface plasmon resonance (SPR) of Ag nanoparticles (NPs)

17

by the near-field electromagnetic enhancement or abundant hot electrons injection and p-n heterojunction

18

of MoS2/BiVO4 by the built-in electrical potential synergistically boost the electron-hole pair separation,

19

transfer properties and suppress the recombination of the electron-hole pairs. Consequently, the

20

BiVO4-Ag-MoS2 electrode among four of the BiVO4-based electrodes achieves the largest photocurrent

21

density of 2.72 mA cm-2 at 0.6 V vs. RHE, which is 2.44 times higher than that of pure BiVO4 electrode

22

(0.79 mA cm-2), and possesses the largest IPCE of 51% at 420 nm. This work proposes a worthy design

23

strategy for a plasmon enhanced p-n heterojunction for efficient PEC water splitting.

24

Keywords: BiVO4; p-n heterojunction; SPR; charge separation; carrier transfer; water splitting

25

Introduction

26

Exploring new methods of utilizing solar energy is essential to solve problems associated with the energy

27

crisis, sustainability and environmental emissions of our society. One of the best pathways of harvesting

28

solar energy is photoelectrochemical (PEC) water splitting via semiconductor electrodes, which has the

29

grand prospect of exploiting photon energy to drive reactions directly from water to storable hydrogen

30

energy.1 Recently, a promising candidate, monoclinic scheelite bismuth vanadate (m-BiVO4) with a direct,

31

low band gap energy (Eg) of ~2.4 eV, has been a research hotspot because of its capable photoactivity in

32

the visible light region for PEC water splitting.2

Shanghai Advanced Research Institute, Chinese Academy of Sciences, No.99, Haike Road,

33

BiVO4 presents the following virtues: nontoxicity, inexpensiveness, and chemical stability.2 However,

34

several issues need to be addressed, including poor separation of electron-hole pairs,2 slow charge-carrier

35

transfer mobility, short carrier diffusion lengths and significant recombination of electron-hole pairs,3

ACS Paragon Plus Environment

1

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 19

1

which have limited the performance of BiVO4 for PEC water splitting. Owing to suffering from these

2

problems, BiVO4 is not able to reach its theoretical maximum photocurrent density of 7.5 mA cm-2.4

3

Recently, various strategies have been investigated to improve the performance of BiVO4, for example,

4

shortening the charge-carrier transfer length by morphology control,5 increasing the active surface ratio by

5

crystal facet studies,6-7 broadening the spectral absorption by metal ion doping,3, 8-9 enhancing oxygen

6

evolution kinetics by oxygen evolution catalyst loading,3, 5, 10 improving the charge separation and transfer

7

by heterojunction engineering,11-14 and restraining the electron-hole pair recombination by noble metal

8

deposition.15-16 To meliorate the poor separation of electron-hole pairs, improve the transfer properties and

9

restrict the recombination of electron-hole pairs, BiVO4-based heterojunctions have attracted scientific

10

attention. For example, various heterojunctions, such as Al-doped ZnO/BiVO4,12 CuWO4/BiVO4,13 and

11

WO3/BiVO4,14 have been constructed. These heterojunctions are composed with two n-type semiconductors

12

with matching band gaps bonded to build a highly efficient heterostructure, in which the most suitable

13

structure is a staggered band gap type (type-II).17 Based on the above considerations, it is more effective for

14

PEC water splitting to apply a p-n-type semiconductor heterojunction with a built-in electrical potential

15

whose direction from an n-type semiconductor to a p-type semiconductor than the n-n-type semiconductor

16

heterojunction, besides benefiting from type-II heterojunctions.18

17

For the p-n-type semiconductor heterojunction, electrons and holes move in the opposite directions by

18

the built-in electrical potential from the diffusion of electrons and holes in the space-charge region to

19

achieve separation of electron-hole pairs and attain robust transfer properties. For example, BiOI/BiVO4,18

20

BiOCl/BiVO4,19 Co3O4/BiVO4,20 NiO/BiVO4,10 and Cu2O/BiVO4

21

p-n-type heterojunction as the efficient architectures to enhance PEC performance; however, these p-type

22

materials don’t deliver a broad-spectrum absorption due to large band gap energy. Considering that

23

two-dimensional few-layered molybdenum disulfide (MoS2) nanosheets are a feasible material for

24

heterojunctions, they not only exist suitable band gap energy with a direct Eg of ~1.9 eV to absorb visible

25

light and match with BiVO4, but also exhibit an ultrahigh specific surface area and numerous exposed

26

active edge sites, in contrast to bulk MoS2 with an indirect Eg of 1.3 eV.22-24 Recently, the MoS2-based

27

composite electrodes for the PEC water splitting have been reported25-26 and MoS2/BiVO4 has been utilized

28

for photocatalytic oxidation and reduction with theoretical support proving its feasibility.23, 27-28 However,

29

MoS2/BiVO4 has been rarely studied for PEC water splitting.

21

have been identified BiVO4-based

30

Furthermore, Ag nanoparticles (NPs) with surface plasmon resonance (SPR) could serve as antennas to

31

control the location of generated charge carriers and localize the optical energy distribution by near-field

32

electromagnetic enhancement or abundant hot electrons injection for PEC water splitting.15, 29-33 In this

33

work, we design a novel integrated Ag-embedded MoS2/BiVO4 p-n heterojunction ternary composite

34

electrode. This electrode possesses a nanoporous n-type BiVO4 using a modified electrodeposition and

35

annealing route to prepare a high specific surface area and shorten diffusion lengths for photoexcited charge

36

carriers. BiVO4 and MoS2 construct a p-n heterojunction to boost its poor electron-hole separation and

37

transport properties using the built-in electrical potential. Simultaneously, the enhanced PEC performance

38

of BiVO4 for the BiVO4-Ag-MoS2 electrode would be verified by the synergistic effect of the p-n

39

heterojunction and SPR of Ag NPs. This work might prompt further exploration of diverse plasmon

40

enhanced p-n heterojunctions devoted to PEC water splitting and photocatalysis.


2

Page 3 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

Experimental section

2

Preparation of the BiVO4-Ag electrodes: The BiVO4 electrodes were fabricated by electrochemical

3

deposition and annealing processes using a modified method that was initially demonstrated by T. W. Kim

4

and K. S. Choi in 2014.5 Ag NPs were synthesized by a revised method described by Aleksey Ruditskiy and

5

Younan Xia in 2016.34 The detailed fabrication process of BiVO4 and Ag NPs are presented in the

6

supporting information (SI).

7

Ag NPs-decorated BiVO4 electrodes were prepared using an electrophoretic deposition process. Anodic

8

deposition was potentiostatically performed at 2 V vs. fluorine-doped tin oxide (FTO) counter electrode at

9

room temperature for 4-8 min with a two-electrode system to deposit Ag NPs. Then, the BiVO4-Ag

10

electrodes were rinsed with distilled water and dried under ambient environment.

11

Construction of the BiVO4-MoS2 and BiVO4-Ag-MoS2 heterojunction electrodes: Similarly, the

12

BiVO4-MoS2 and BiVO4-Ag-MoS2 heterojunction electrodes were prepared using an electrophoretic

13

deposition process. Anodic deposition was potentiostatically conducted at 1 V vs. FTO electrode, and the

14

BiVO4-based electrodes were used as a counter electrode at room temperature for 1-5 min with a

15

two-electrode system to deposit the layered MoS2 nanosheets purchased from Nanjing Jcnano Co., Ltd.

16

Then, the BiVO4-MoS2 and BiVO4-Ag-MoS2 electrodes were rinsed with distilled water and dried under

17

ambient environment. Finally, the electrodes were annealed in 10% H2/N2 at 350 °C for 2 h with a ramping

18

rate of 2 °C per min to ensure that the MoS2 nanosheets tightly contacted with the BiVO4-based electrodes.

19

Characterization: The purity and crystallinity of BiVO4 was determined by X-ray diffraction (XRD,

20

Bruker AXS D8 Advance) with Cu Kα radiation (λ= 1.5418 Å). The morphologies of the samples were

21

examined by field-emission scanning electron microscopy (SEM, Hitachi Situation-4800) at an accelerating

22

voltage of 5 kV. Elemental compositions were determined by energy dispersive X-ray spectroscopy (EDX,

23

EDX detector on the Hitachi Situation-4800). Transmission electron microscopy (TEM, JEOL 2100F)

24

images were obtained at an accelerating voltage of 200 kV. The layered MoS2 nanosheets on the Si

25

platform were confirmed by atomic force microscopy (AFM, NT-MDT). The valence states of the elements

26

were determined by X-ray photoelectron spectroscopy (XPS, PHI 5400) using Mg Kα radiation (1253.6

27

eV). All XPS spectra were calibrated to C 1s = 284.8 eV. UV-vis spectra were recorded using a Cary 5000

28

UV-vis-NIR spectrophotometer in diffuse reflectance mode.

29

Photoelectrochemical measurements: All PEC water splitting reaction measurements were carried out

30

with an electrochemical workstation (CHI 760E, CH Instruments Inc.) using a standard three-electrode

31

system with a flat quartz window cell. The as-prepared BiVO4-based electrodes were used as the working

32

electrode, an Ag/AgCl (4 M KCl) electrode was used as the reference electrode, and platinum foil was used

33

as the counter electrode in a 0.1 M potassium phosphate buffer with and without 1 M Na2SO3 solution (pH

34

7). The illumination measurements were conducted under simulated AM 1.5G solar illumination with a 500

35

W xenon lamp, and the light intensity was calibrated to 100 mW cm−2 by the standard reference of a

36

Newport 91150 silicon solar cell. The linear scanning voltammetry (LSV) curves were obtained with a scan

37

rate of 10 mVs-1. The Mott-Schottky experiments were conducted using a setting frequency of 1000 Hz in

38

the dark. Electrochemical impedance spectroscopy (EIS) measurements were conducted under AM 1.5G

39

(100 mW cm-2) illumination from 100 kHz to 1 Hz. The entire working electrodes were illuminated through

40

the back of the FTO glass. Incident photo-to-current conversion efficiency (IPCE) was measured on a


3


Page 4 of 19

1

commercial monochromator amplifier assembly (Zolix Solar Cell Scan 100) in a three-electrode cell at 0.6

2

V vs. the reversible hydrogen electrode (RHE) from 380 to 600 nm from a Xe arc lamp referenced to a

3

calibrated standard Si solar cell at room temperature. The gas products were measured using an online gas

4

chromatograph (GC9860, Shanghai Fanwei Equipment Co., Ltd) and before the equipment for testing, air

5

was thoroughly purged by argon (Ar) for 1 h.

6

Results and Discussion

7

Figure 1. Electron microscopic characterization of the BiVO4, BiVO4-MoS2, BiVO4-Ag and

8

BiVO4-Ag-MoS2 electrodes. SEM top-view images of (a) BiVO4, (b) BiVO4-MoS2, (c) BiVO4-Ag, (e)

9

BiVO4-Ag-MoS2 and cross-sectional views image of (d) BiVO4; (f) SEM image of BiVO4-Ag-MoS2 and

10

the corresponding SEM-EDX elemental mapping images for S, Mo, Ag, Bi, V, O; (g) TEM (inset is

11

HRTEM) image of Ag NPs, (h) TEM image of MoS2 and (i) AFM image of MoS2.

12

The columnar particles of BiVO4 with a thickness of 1.2 µm (Figure 1e) were prepared on FTO substrates

13

from SEM top-view images of BiVO4 electrode, as well as the electrodes decorated with MoS2, Ag and


4

Page 5 of 19

1

Ag/MoS2 (Figure 1a-c and e). Ag NPs, as indicated by the red dashed arrow (Figure 1c, e), are dispersed on

2

the BiVO4 electrodes with a mean size of 50 nm (Figure 1g), which presents a lattice spacing of 0.14 nm

3

corresponding to the (220) planes of Ag (JCPDS #01-1164) (Figure 1g inset image). MoS2 layered structure

4

of ~ 1 nm confirmed by TEM (Figure 1h) and AFM (Figure 1i), as indicated by the blue dashed rectangle

5

(Figure 1b, e), are decorated on the BiVO4 and BiVO4-Ag electrodes to construct MoS2/BiVO4

6

heterojunction. However, the part of the layered MoS2 nanosheets aggregated when the composite

7

electrodes were annealed in 10% H2/N2 at 350 °C for 2 h, but there are still the few-layered MoS2 sheets

8

even after they aggregate (Figure 1f). The elemental mapping images for S, Mo, Ag, Bi, V, O of the

9

BiVO4-Ag-MoS2 electrode were verified by EDX from SEM image (Figure 1f), and the signals of the

10

different elements are clearly observed. (a)

(b) Ag 3d5/2

Intensity (a.u.)

Intensity (a.u.)

BiVO4

20

30

40

50

60

(c)

376

374

372

370

(d)

366

S 2p3/2

229.0 eV

232.1 eV 226.2 eV S 2s

228

226

S 2p1/2

Intensity (a.u.)

Mo 3d3/2

230

368

Binding Energy (eV)

Mo 3d5/2

232

267.8 eV

Ag 3d3/2 273.8 eV

2θ

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


164

Binding Energy (eV)

161.8 eV

162.8 eV

163

162

161

160

Binding Energy (eV)

11

Figure 2. (a) XRD pattern of BiVO4. Vertical lines indicate the JCPDS diffraction peaks of FTO (blue) and

12

monoclinic scheelite BiVO4 (red, JCPDS #14-0688). XPS spectra of (b) the Ag 3d peaks (c) Mo 3d peaks

13

and (d) S 2p peaks of the BiVO4-Ag-MoS2 electrodes

14

The purity and highly crystalline nature of the nanoporous monoclinic scheelite structure were confirmed

15

by sharp peaks of XRD pattern (Figure 2a), along with SnO2 peaks originating from FTO substrate. Figure

16

2b, c and d display XPS spectra of Ag 3d, Mo 3d and S 2p for the BiVO4-Ag-MoS2 electrode, respectively.

17

The characteristic Ag 3d3/2 and 3d5/2 peaks are located at 273.8 and 267.8 eV, which corresponds to metallic

18

Ag with a surface concentration of 3%. And the Mo 3d3/2, Mo 3d5/2, S 2p1/2, and S 2p3/2 peaks are located at

19

232.1, 229.0, 162.8, and 161.8 eV, respectively, which are lower than those of the values reported for pure


5


1

MoS2 (232.5, 229.3, 163.3, and 162.3 eV, respectively).35 The binding energies of the BiVO4-Ag-MoS2

2

electrode decrease comparing to those of pure MoS2 due to the formation of the MoS2/BiVO4 p-n

3

heterojunction.28 In the corresponding survey scan (Figure S1), the Bi 4f, V 2p and O 1s peaks for the

4

BiVO4-Ag-MoS2 electrode agree with previous reports.2 E (V vs. RHE)

E (V vs. RHE) 0.2

(a)

0.4

0.6

0.8

1.0

1.2

0.2

1.4

5

(b) J (mA cm-2)

-2

J (mA cm )

3 2 1 0 -0.6

-0.4

1.0

1.2

1.4

-0.2

0.0

0.2

0.4

0.6

4 3 2

0 -0.6

0.8

in the dark -0.4

(d)

ηtrans (%)

0.98%

1.0

0.79%

0.5

0.4

0.6

0.8

1.0

0.8

60 40

0.4

0.6

100

1.0

1.2

4

IPCE (%)

( αhv)2

(f)

80

IPCE (%)

0.0 2.4 2.6 Eg (eV)

0.4

0.8

E (V vs. RHE)

0.5

0.6

0.6

0

1.2

1.0

0.8

0.4

100

E (V vs. RHE) 1.0

0.2

20

0.49% 0.2

0.0

80

1.50%

0.0 0.0

-0.2

E (V vs. Ag/AgCl)

2.0

1.5

ABPE (%)

0.8

5

E (V vs. Ag/AgCl)

(e)

0.6

7

1

in the dark

(c)

0.4

6

4

Absorbance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 19

60

2 0 500 550 600 Wavelength (nm)

40 20

0.2

0

0.0 400

450

500

550

600

650

400

Wavelength (nm)

450

500

550

600

Wavelength (nm)

5

Figure 3. PEC performance of the BiVO4 (black), BiVO4-MoS2 (green), BiVO4-Ag (red) and

6

BiVO4-Ag-MoS2 (blue) electrodes. LSV curves in the dark (dashed lines) or under AM 1.5G (100 mW cm-2)

7

illumination (solid lines) in 0.1 M phosphate buffer (pH 7) (a) without and (b) with 1 M Na2SO3 as a hole

8

scavenger. (c) ABPE curves calculated from (a) LSV curves. (d) Surface charge transfer efficiency (ηtrans)

9

calculated from (a, b) LSV curves. (e) UV-vis absorption spectra (inset is the corresponding Tauc plot of

10

the BiVO4 electrode) and (f) IPCE spectra collected at an incident wavelength range from 380 to 600 nm


6

Page 7 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

(inset shows the wavelength range from 500 to 600 nm) at 0.6 V vs. RHE in 0.1 M phosphate buffer (pH 7).

2

The significance of the BiVO4 electrodes decorated with MoS2, Ag and Ag/MoS2 were confirmed by the

3

systemic PEC performance of the BiVO4-based electrodes in 0.1 M phosphate buffer (pH 7) within and

4

without 1 M Na2SO3 aqueous solution as a hole scavenger, in the dark or under AM 1.5G illumination

5

(Figure 3). Figure 3a compares LSV curves of the BiVO4, BiVO4-MoS2, BiVO4-Ag and BiVO4-Ag-MoS2

6

electrodes in 0.1 M phosphate buffer (pH 7). The pure BiVO4 electrode reveals photocurrent densities of

7

0.79 and 2.14 mA cm-2 at 0.6 and 1.23 V vs. RHE, respectively, that are much larger than those in previous

8

reports5,

9

increased active areas. Both the BiVO4-Ag and BiVO4-MoS2 electrodes display larger photocurrent

10

densities than that of the pure BiVO4 electrode under the same conditions due to the decoration with Ag

11

NPs or MoS2. The photocurrent densities of the BiVO4-Ag-MoS2 electrode are the highest among all the

12

BiVO4-based electrodes, reaching 2.72 and 4.02 mA cm-2 at 0.6 and 1.23 V vs. RHE, respectively, which

13

are 3.44 and 1.88 times comparing to those of the pure BiVO4 electrode. The optimal contents of the Ag

14

NPs and MoS2 were chosen based on the results (Figure S2), and the optimal deposition time of Ag NPs

15

and MoS2 were 6 min and 3 min, respectively. All the electrodes used for testing were prepared under the

16

optimal deposition time. Examining the photocurrent density for sulfite oxidation can provide information

17

on the PEC performance of the BiVO4-based electrodes irrespective of its poor water oxidation kinetics

18

because sulfite oxidation is kinetically and thermodynamically easier than water oxidation. In sulfite

19

oxidation, the rate of charge transfer to the electrolyte interface is very quick, and thus, surface

20

recombination of charges can be considerable negligible. Thus the PEC performance were further measured

21

containing 1 M Na2SO3 as a hole scavenger (Figure 3b). Surface charge transfer efficiency of sulfite

22

oxidation [ηtrans (Na2SO3)] are close to 100%,2, 5 as confirmed in Figure S3, and the photocurrent densities

23

of the BiVO4-based electrodes are stable under potentiostatic conditions containing 1 M Na2SO3 as a hole

24

scavenger, however, the photocurrent densities of the BiVO4-based electrodes gradually decay without 1 M

25

Na2SO3. A comparison of the results (Figure 3a) reveals that the BiVO4-Ag-MoS2 electrode possesses the

26

largest photocurrent densities of 4.16 and 5.94 mA cm-2 at 0.6 and 1.23 V vs. RHE, respectively (Figure

27

3b).

36

owing to the thermal pre-treatment to promote the crystal growth and create the probably

28

Applied bias photo-to-current efficiency (ABPE) of the BiVO4-based electrodes was calculated using

29

LSV curves (Figure 3a) with practical Faradaic efficiency for H2 evolution (see Figure 5b)5, 37 and the

30

results are plotted in Figure 3c. The BiVO4-Ag-MoS2 electrode shows a much larger PEC water splitting

31

efficiency of 1.50% at a much smaller bias voltage of 0.57 V vs. RHE, and this electrode achieves the

32

highest PEC water splitting efficiency of 2.67% at 0.53 V vs. RHE in the presence of the hole scavenger

33

(Figure S4) than others’ BiVO4-based electrodes, which is an extremely beneficial characteristic for

34

constructing a PEC diode or a tandem cell.5

35

Surface charge transfer efficiency of water oxidation [ηtrans (H2O)] was calculated from LSV curves

36

(Figure 3a, b)5, 36, 38 and were plotted in Figure 3d. ηtrans (H2O) of 67% for the BiVO4-Ag-MoS2 electrode at

37

1.23 V vs. RHE display the best performance, followed by 59% for the BiVO4-Ag electrode, 54% for the

38

BiVO4-MoS2 electrode and 43% for the pure BiVO4 electrode. In addition, charge separation efficiency

39

(ηsep) was calculated from IPCE curves with the standard solar spectrum of the electrodes and plotted

40

(Figure S5), which represents the yield of electron-hole pair separation. The BiVO4-Ag-MoS2 electrode


7


Page 8 of 19

1

achieves the greatest ηsep of 75% at 1.23 V vs. RHE, followed by 70% for the BiVO4-Ag and BiVO4-MoS2

2

electrodes, 62% for the pure BiVO4 electrode. These indicate MoS2/BiVO4 heterojunction can improve

3

surface charge transfer efficiency of PEC water splitting for electron-hole pair separation and charge carrier

4

transport at the interfaces of BiVO4 and MoS2 by the built-in potential of MoS2/BiVO4 heterojunction.

5

Moreover, electrodes decorated with Ag NPs demonstrate more superior catalysis property owing to SPR

6

effect of Ag NPs.

7

The light absorption ability and the photon-to-charge conversion efficiency of the BiVO4-based

8

electrodes are considered to evaluate the effect of incorporating Ag NPs and MoS2. The absorption edges of

9

the BiVO4 electrodes are at ~505 nm and the Eg of the BiVO4 electrode is approximately 2.46 eV from the

10

corresponding inset Tauc plots in agreement with previous report (Figure 3e).5 At wavelengths higher than

11

505 nm, the BiVO4-Ag, BiVO4-MoS2, and BiVO4-Ag-MoS2 electrodes demonstrate slightly larger

12

absorption intensity than the pure BiVO4 electrode due to the absorption from MoS2 and SPR absorption of

13

Ag NPs, because the absorption of Ag NPs covered from 300 to 650 nm and the absorption peak was

14

located at 420 nm (Figure S6a). Meanwhile, IPCE is measured to understand the photon-to-charge

15

conversion efficiency, involving photon absorption, charge-carrier excitation, electron-hole pair separation,

16

charge transport from the solid to the solid-liquid interface and interfacial charge transfer across the

17

solid-liquid interface, to provide understanding of the PEC performance of the electrodes.37 IPCE was

18

measured at 0.6 V vs. RHE in 0.1 M phosphate buffer (pH 7) (Figure 3f). The photoactive range of the

19

BiVO4-based electrodes cover 380–550 nm, slight shorter than light absorption spectra, but longer than that

20

of the pure BiVO4 electrode. Evidently, IPCE of the BiVO4-Ag-MoS2 electrode reaches 51% at 420 nm,

21

which is superior to those of the BiVO4-Ag (32%), BiVO4-MoS2 (24%) and pure BiVO4 (18%) electrodes.

22

Similarly, IPCE of the BiVO4-Ag-MoS2 electrode is ~75% at 420 nm, superior to those of the BiVO4-Ag,

23

BiVO4-MoS2 and pure BiVO4 electrodes in the presence of the hole scavenger (Figure S7). In addition,

24

APCE is used to represent the efficiency of photocurrent collected per incident photon absorbed.37 The

25

BiVO4-Ag-MoS2 electrode exhibits the highest APCE of 57% and 86% at 420 nm among all the

26

BiVO4-based electrodes without and with 1 M Na2SO3 as a hole scavenger, respectively (Figure S8). As

27

stated above, absorption spectra of the BiVO4 electrodes could be broadened and the photon-to-charge

28

conversion efficiency could be improved by introducing Ag and MoS2 owing to the synergistic beneficial

29

effect of SPR excitation of Ag NPs and p-n heterojunction of MoS2/BiVO4.

30

The charge transfer kinetics in the heterostructured composites and the interfacial properties between the

31

electrodes and electrolyte were investigated by EIS responses of BiVO4-based electrodes at 0.6 V vs RHE

32

under illumination (AM 1.5 G) (Figure 4a). EIS Nyquist plots fitted according to the equivalent Randles

33

circuit model, as shown in the right inset of the figure, where RS, CPE and RCT represent the solution

34

resistance, constant phase element and charge-transfer resistance at the interface of semiconductor and

35

electrolyte, respectively.39 The fitted RS values are 32, 28, 26 and 25 Ω cm2 for the pure BiVO4,

36

BiVO4-MoS2, BiVO4-Ag and BiVO4-Ag-MoS2 electrodes, respectively, which demonstrates that the

37

interfaces among BiVO4, Ag and MoS2 decreased the solution resistance (Table S1). The fitted RCT values

38

extracted from semicircle radii are 448, 295, 243 and 195 Ω cm2 for the pure BiVO4, BiVO4-MoS2,

39

BiVO4-Ag and BiVO4-Ag-MoS2 electrodes, respectively (Table S1). The RCT values of the BiVO4-MoS2

40

and BiVO4-Ag electrodes are smaller than that of the pure BiVO4 electrode. The RCT of the


8

Page 9 of 19

1

BiVO4-Ag-MoS2 electrode exhibits the lowest value among all the BiVO4-based electrodes because the p-n

2

heterojunction of MoS2/BiVO4 and SPR excitation of Ag NPs promote charge transfer at the interface of

3

the semiconductor and electrolyte. Similar results are demonstrated in Figure S10a with measurements in

4

the presence of the hole scavenger. The intrinsic electronic structures of the electrodes were analysed by

5

Mott-Schottky plots. As shown in Figure 4b, the Mott-Schottky plots of the four different electrodes in 0.1

6

M phosphate buffer (pH 7) with 1 M Na2SO3 were measured. If surface charge recombination is ignored,

7

the BiVO4-Ag-MoS2 and BiVO4 electrodes show the smallest and largest photocurrent onset potential

8

among four different BiVO4-based electrodes, respectively, indicating that the electrodes with Ag NPs and

9

MoS2 decoration are easier to react. Meanwhile, the flat band potential (EFB) approaches the photocurrent

10

onset potential for sulfite oxidation due to fast oxidation kinetics,5 and thus, we can deduce that the

11

BiVO4-Ag-MoS2 electrode has the lowest EFB, and the BiVO4 electrode has the highest EFB, where the flat

12

band potential was obtained from the x-axis intercept. In addition, the charge carrier density (ND) in these

13

electrodes can be calculated from the slopes of the Mott-Schottky plots.2 ND of the BiVO4, BiVO4-MoS2,

14

BiVO4-Ag and BiVO4-Ag-MoS2 electrodes gradually increase from 1.851018 cm-3 to 2.741018 cm-3

15

(Table S2). Meanwhile, the Fermi level of BiVO4 for the BiVO4-Ag-MoS2, BiVO4-Ag and BiVO4-MoS2

16

electrodes will increase as the charge carrier density increases, which causes increased effective band

17

bending in the space-charge region than pure BiVO4, owing to a bigger difference between the redox

18

potential of the electrolyte and the Fermi level of BiVO4 2. The water splitting results are shown in Figure

19

S10b. E (V vs.RHE)

(b)

2

RS

20

CPE

20

40

-Z'' (Ω cm2)

9

0

0.1

0.2

0.3

0.4

3

-2

0

200

4

RCT 4

250

40

C (10 F cm )

2

-Z'' (Ω cm )

(a) 300

-Z'' (Ω cm )

150

2

-2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

1 50 0 0

50

100

150

200

250

300

0 -0.6

2

-0.5

-0.4

-0.3

-0.2

E (V vs. Ag/AgCl)

Z' (Ω cm )

20

Figure 4. (a) EIS Nyquist plots of the BiVO4 (black), BiVO4-MoS2 (green), BiVO4-Ag (red) and

21

BiVO4-Ag-MoS2 (blue) electrodes in 0.1 M phosphate buffer (pH 7). (b) Mott-Schottky plots of the BiVO4

22

(black), BiVO4-MoS2 (green), BiVO4-Ag (red) and BiVO4-Ag-MoS2 (blue) electrodes in 0.1 M phosphate

23

buffer with 1 M Na2SO3 (pH 7).


9


(b) 4

H 2 or O 2 evolved (µmol)

(a)

J (mA cm 2)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

3

2

1

0

0

2

4

t (h)

6

8

10

Page 10 of 19

O2

600

H2 400

200

0 0

2

4

t (h)

6

8

10

1 2

Figure 5. Operational stability of the BiVO4-Ag-MoS2 electrode. (a) The J-t curve collected at 1.23 V vs.

3

at 1.23 V vs. RHE (dotted), and the calculated H2 and O2 evolution from curve a (dashed lines).

RHE under AM 1.5G illumination in 0.1 M phosphate buffer (pH 7). (b) Detection of H2 and O2 evolution

4

As shown in Figure 5a, the operational stability of the BiVO4-Ag-MoS2 electrode was tested by

5

chronoamperometry (J-t curve) at 1.23 V vs. RHE under AM 1.5G illumination in 0.1 M phosphate buffer

6

(pH 7). The H2 and O2 evolution are measured by integration of the GC (Figure 5b), the total amounts of H2

7

evolution and O2 evolution are 578 µmol and 297 µmol after 10 h test. The molar ratio of produced H2/O2 is

8

1.95:1 with about 90% and 88% Faradaic efficiencies for O2 and H2 evolution, respectively. Such a ratio of

9

H2/O2 is very close to the theoretical one of 2:1, and expounds that nearly no side-reaction occurred during

10

water splitting. Besides, the operational stability of the BiVO4, BiVO4-Ag, and BiVO4-MoS2 electrodes are

11

shown in Figure S12. The amounts of H2 and O2 evolution increase after Ag NPs or MoS2 decorated on

12

BiVO4. Thus, Ag NPs and MoS2 combined with BiVO4 could efficiently promote OER, consistent with

13

PEC performance as shown in Figure 3. After BiVO4 was decorated with MoS2 and Ag NPs, the

14

photocurrent stability of the BiVO4-based electrodes is enhanced and shows the superlative stability with a

15

decay of approximately 14% after 10 h (Figure 5), which demonstrates that MoS2/BiVO4 p-n

16 17 18 19 20 21 22 23 24 25 26 27 28

heterojunction and SPR effect of Ag NPs boost a collaborative enhanced PEC stability. The BiVO4-Ag-MoS2 composite after the PEC test is examined by SEM (Figure S13) to study the impact of the prolonged photoelectrolysis on morphology. The main structure of the BiVO4-Ag-MoS2 composite after test do not significantly change, but it is rougher than that before the tests (Figure 1e), and the sizes of BiVO4 and Ag NPs only increase a little, which might decrease the activity site density and be the reason for the decay of activity as shown in the durability test. The physicochemical properties are characterized after the PEC. As shown in Figure S14, all the diffraction peaks of BiVO4 still exist after the PEC test, indicating that PEC tests do not change the crystal phase of BiVO4, while no obvious peaks for MoS2 and Ag NPs could be detected in the composite before and after the test, probably due to the high dispersion and small percentage of MoS2 and Ag NPs. Figure S15 shows XPS spectra of Ag 3d, Mo 3d and S 2p. One could not observe an obvious shift in the spin orbital peaks although their contents become smaller than those before test (Figure 2b, c and d), thus demonstrating the stable physicochemical states for MoS2 and Ag NPs after PEC tests.


10

Page 11 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

Figure 6. Spatial distributions of the electric field by FDTD simulations for (a) the BiVO4-Ag and (b)

2

BiVO4-Ag-MoS2 electrodes with excitation wavelengths of 420 nm. Incident light is along the z-axis

3

direction. (c) Linear distributions of the electric field at x=40 nm along the z axis of the BiVO4-Ag and

4

BiVO4-Ag-MoS2 electrodes (red dashed lines in Figure 7a, b). (d) Linear distributions of the electric field at

5

Z=50 nm and 100 nm along the x axis of the interfaces of the BiVO4-Ag and BiVO4-Ag-MoS2 electrodes

6

(yellow dashed lines in Figure 7a, b). The color bar shows the electric field intensity.

7

The related possible enhancement mechanisms of the p-n heterojunction and SPR of Ag NPs are further

8

elaborated. Finite difference time domain (FDTD) simulations were implemented to simulate the electric

9

field spatial distributions across the interfaces of the different substances and understand the energy-transfer

10

processes as a function of the incident light wavelength to explore the potential mechanism of SPR

11

excitation of Ag NPs enhancing the PEC water splitting performance. Considering the complexity of the

12

structure and simulation, Figures 6 and S16 show the representative FDTD simulations of the most


11


Page 12 of 19

1

probable construction for the BiVO4-Ag and BiVO4-Ag-MoS2 electrodes at an excitation wavelength of

2

420 nm, which corresponds to the absorption peak of Ag NPs (Figure S6a). The electric field intensity at

3

Ag and BiVO4 interface is higher than that at Ag and MoS2 interface because light radiates from the back of

4

BiVO4 (Figures 6a, b, c and S16), and the electric field possesses a spatially inhomogeneous distribution

5

with the highest intensity near the interface of the nanostructures, reducing with the distance from the

6

interface. This result would deduce the function of plasmonic Ag NPs as antennas to control the location of

7

generated charge carriers and localize the optical energy distribution by near-field electromagnetic near the

8

interface of the nanostructures (Figure 6a, b, d). Meanwhile, hot-electrons injection might play a dominant

9

role at the interface of the nanostructures under the enhanced electric field.

10

Furthermore, the enhancement mechanism of the p-n heterojunction is elucidated. The Eg of 2.42 eV for

11

m-BiVO4 estimated by the hybrid HSE06 functional agrees well with the experimental result (2.46 eV).23, 40

12

Few-layered MoS2 is a direct Eg (1.92 eV) semiconductor, consistent with experiments (1.90 eV).23-24 Due

13

to the introduced strains and the van der Waals (vdW) interactions of MoS2 (001) (1.64 eV) and m-BiVO4

14

(010) (2.24 eV) surface, the Eg of the MoS2 (001)/m-BiVO4 (010) heterojunction narrows to 2.05 eV, thus

15

achieving a typical band gap value for visible-light-driven photoactivity.23-24, 40 The partial density of states

16

(PDOS) of the structures shows the valence band maximum (VBM) mainly originates from the MoS2 states,

17

while the conduction band minimum (CBM) is dominated by BiVO4 states.23 The MoS2/BiVO4

18

heterojunction forms a type-II band alignment with a staggered band gap and it exists the built-in potential

19

between the CBM of BiVO4 and MoS2 (Figure 7b).23

20

Figure 7. Schematic diagrams of the proposed band gap diagram of BiVO4, Ag and MoS2 (a) before and (c)

21

after contact with each other and (b) formation of the MoS2/BiVO4 p-n heterojunction. Evac, vacuum energy;

22

Ef, Fermi energy; CB, conduction band; VB, valence band; ϕm, metal work function; ϕSB, semiconductor

23

work function; χs, electron affinity of the semiconductor.


12

Page 13 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

As presented by the schematic diagrams of the proposed band gap diagrams in Figure 7c. The

2

photo-generated electrons could be excited from the VB into the CB, and electrons transfer from the CB of

3

MoS2 to the CB of BiVO4 and accumulate on the CB of BiVO4 for the hydrogen evolution reaction on the

4

Pt counter electrode. At the same time, the holes for the oxygen evolution reaction could transfer from the

5

VB of BiVO4 to the VB of MoS2, which could readily transfer charge carriers and transfer the

6

photo-generated electrons from MoS2 to the BiVO4 surface, resulting in effective separation (Figure 7b, c).

7

Briefly, the separation, recombination and interfacial transfer of photo-induced charge carriers could be

8

rewardingly influenced by the built-in potential and matched band gap energy. Further, Ag NPs are

9

embedded in MoS2/BiVO4 heterojunction. The Schottky barriers could be formed, when the metal and

10

semiconductor combine, and then, the band edge energies of the semiconductors could be constantly shifted

11

due to the electric field at the interface, leading to charge transfer, i.e., band bending, in the space-charge

12

region. The Fermi energy (Ef) of the different nanostructures would attain the same level 41, which would

13

prevent back electron transfer to Ag NPs and favour electron accumulation in the CB of MoS2 or BiVO4.

14

Meanwhile, under light illumination, Ag NPs absorb resonant photons, and then, energetic hot electrons

15

would be generated and induce an enhanced local electric field from SPR excitation.31 The local electric

16

field would facilitate the separation of electron-hole pairs and carrier transport from the Ag NPs to BiVO4

17

or MoS2. The hot electrons would pass over the Schottky barrier at the BiVO4/Ag and MoS2/Ag interfaces

18

and inject into the CB of BiVO4 and MoS2 to promote charge-carrier accumulation and contribute to an

19

escalated charge carrier concentration in the two kinds of semiconductors, thus SPR of Ag NPs would

20

further enhance the built-in potential of p-n heterojunction. Finally, the prominent separation and delayed

21

recombination of electron-hole pairs and rapid charge carrier mobility would be achieved owing to the

22

MoS2/BiVO4 heterojunction with a staggered band gap and built-in potential whose direction from n-type

23

BiVO4 to p-type MoS2, along with SPR enhancement of Ag NPs by the near-field electromagnetic

24

enhancement or abundant hot electrons injection.

25

Conclusions

26

In conclusion, the BiVO4-based electrodes were designed and confirmed to possess enhanced PEC water

27

splitting activity. The electrodes were prepared using a convenient electrodeposition and electrophoretic

28

deposition process. The PEC performance of the BiVO4-Ag-MoS2 electrode is noticeably enhanced

29

comparing to the BiVO4 electrode. More facile water oxidation is achieved, displaying the lowest onset

30

potential and largest photocurrent density of 2.72 mA cm-2 at 0.6 V vs. RHE among all the BiVO4-based

31

electrodes, which is 2.44 times larger than that of the pure BiVO4 electrode (0.79 mA cm-2). In addition, we

32

deduce the effective separation of electron-hole pairs (ηsep of 75% at 1.23 V vs. RHE), the rapid transfer

33

mobility of charge carriers (ηtrans of 67% at 1.23 V vs. RHE), and the prominent photon-to-current

34

conversion efficiency (IPCE of 51% and APCE of 57% at 420 nm) due to the synergistic effect between

35

SPR of Ag NPs and p-n heterojunction of MoS2/BiVO4. It is noteworthy that the built-in potential from

36

BiVO4 to MoS2 and matched band gap energy of MoS2/BiVO4 p-n heterojunction, as well as the near-field

37

electromagnetic enhancement and hot-electrons injection of Ag NPs with SPR excitation would play a

38

crucial role for enhanced catalytic performance. Furthermore, the plasmon enhanced BiVO4-based p-n

39

heterojunction electrodes are promising research subjects for PEC water splitting.


13


Page 14 of 19

1

Associated content

2

The Supporting Information is available free of charge on the ACS Publications website at DOI:

3

xx.xxxx/acssuschemeng.xxxxxx

4

Further details of the benchmark electrodes fabrication simulation and calculation; Figure S1. XPS spectra

5

of Survey scan, Bi 4f peaks, V 2p peaks and O 1s peaks of the BiVO4-Ag-MoS2 electrode; Figure S2. LSV

6

curves of the BiVO4-Ag electrodes with different electrophoresis time (4, 6, 8 min) and the

7

BiVO4-Ag-MoS2 electrodes with different electrophoresis time (1, 3, 5 min) without and with 1 M Na2SO3;

8

Figure S3. J–t curves of the different electrodes at 1.23V vs. RHE without and with 1 M Na2SO3; Figure S4.

9

ABPE curves of the different electrodes with 1 M Na2SO3; Figure S5. ηsep of the different electrodes;

10

Figure S6. UV-Vis absorption spectrum of Ag NPs and light harvesting efficiencies (

11

electrodes; Figure S7. The corresponding Tauc plots of the different electrodes; Figure S8. IPCE spectra

12

with 1 M Na2SO3 of different electrodes, Figure S9. APCE spectra without and with 1 M Na2SO3 of the

13

different electrodes; Figure S10. Calculated photocurrent densities curves corresponding to different

14

wavelength and the standard solar spectrum of different electrodes; Figure S11. EIS Nyquist plots of the

15

different electrodes with 1 M Na2SO3 and Mott-Schottky plots of the different electrodes; Figure S12.

16

Operational stability of the BiVO4, BiVO4-Ag and BiVO4-MoS2 electrodes. J-t curves and H2 and O2

17

evolution; Figure S13. SEM images of the BiVO4-Ag-MoS2 electrodes before and after PEC tests; Figure

18

S14. XRD pattern of the BiVO4-Ag-MoS2 electrode before and after PEC tests; Figure S15. XPS spectra of

19

survey, the Ag 3d peaks, Mo 3d peaks and S 2p peaks of the BiVO4-Ag-MoS2 electrodes after PEC tests;

20

Figure S16. Spatial distributions of the electric field by FDTD simulations, Table S1. The fitted results of

21

EIS data, and Table S2. Carrier densities (

22

Acknowledgements

23

This work was financially supported by the National Key Research programs (2017YFA0206500), the

24

National Natural Science Foundation of China (21533005, 21503262)

25

References

26 27 28 29 30 31 32 33

(1) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S.,

) of the different

) of the different electrodes

Solar water splitting cells. Chem. Rev. 2010, 110 (11), 6446-6473. DOI: 10.1021/cr1002326 (2) Park, Y.; McDonald, K. J.; Choi, K.-S., Progress in bismuth vanadate photoanodes for use in solar water oxidation. Chem. Soc. Rev. 2013, 42 (6), 2321-2337. DOI: 10.1039/C2CS35260E (3) Zhong, D. K.; Choi, S.; Gamelin, D. R., Near-complete suppression of surface recombination in solar photoelectrolysis by “Co-Pi” catalyst-modified W: BiVO4. J. Am. Chem. Soc. 2011, 133 (45), 18370-18377. DOI: 10.1021/ja207348x (4) Hu, S.; Xiang, C.; Haussener, S.; Berger, A. D.; Lewis, N. S., An analysis of the optimal band gaps of


14

Page 15 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41


light absorbers in integrated tandem photoelectrochemical water-splitting systems. Energy Environ. Sci. 2013, 6 (10), 2984-2993. DOI: 10.1039/C3EE40453F (5) Kim, T. W.; Choi, K.-S., Nanoporous BiVO4 photoanodes with dual-layer oxygen evolution catalysts for solar water splitting. Science 2014, 343 (6174), 990-994. DOI: 10.1126/science.1246913 (6) Li, R.; Zhang, F.; Wang, D.; Yang, J.; Li, M.; Zhu, J.; Zhou, X.; Han, H.; Li, C., Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO4. Nat. Commun. 2013, 4, 1432. DOI:10.1038/ncomms2401 (7) Yang, J.; Wang, D.; Zhou, X.; Li, C., A theoretical study on the mechanism of photocatalytic oxygen evolution on BiVO4 in aqueous solution. Chem. Eur. J. 2013, 19 (4), 1320-1326. DOI: 10.1002/chem.201202365 (8) Su, J.; Liu, C.; Liu, D.; Li, M.; Zhou, J., Enhanced Photoelectrochemical Performance of the BiVO4/Zn: BiVO4 Homojunction for Water Oxidation. ChemCatChem 2016, 8 (20), 3279-3286. DOI: 10.1002/cctc.201600767 (9) Luo, W.; Yang, Z.; Li, Z.; Zhang, J.; Liu, J.; Zhao, Z.; Wang, Z.; Yan, S.; Yu, T.; Zou, Z., Solar hydrogen generation from seawater with a modified BiVO4 photoanode. Energy Environ. Sci. 2011, 4 (10), 4046. DOI: 10.1039/C1EE01812D (10) Zhong, M.; Hisatomi, T.; Kuang, Y.; Zhao, J.; Liu, M.; Iwase, A.; Jia, Q.; Nishiyama, H.; Minegishi, T.; Nakabayashi, M.; Shibata, N.; Niishiro, R.; Katayama, C.; Shibano, H.; Katayama, M.; Kudo, A.; Yamada, T.; Domen, K., Surface Modification of CoOx Loaded BiVO4 Photoanodes with Ultrathin p-Type NiO Layers for Improved Solar Water Oxidation. J. Am. Chem. Soc. 2015, 137 (15), 5053-5060. DOI: 10.1021/jacs.5b00256 (11) Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.; Liu, J.; Wang, X., Semiconductor heterojunction photocatalysts: design, construction, and photocatalytic performances. Chem. Soc. Rev. 2014, 43 (15), 5234-5244. DOI: 10.1039/C4CS00126E (12) Zhang, L.; Reisner, E.; Baumberg, J. J., Al-doped ZnO inverse opal networks as efficient electron collectors in BiVO4 photoanodes for solar water oxidation. Energy Environ. Sci. 2014, 7 (4), 1402. DOI: 10.1039/c3ee44031a (13) Pilli, S. K.; Deutsch, T. G.; Furtak, T. E.; Brown, L. D.; Turner, J. A.; Herring, A. M., BiVO4/CuWO4 heterojunction photoanodes for efficient solar driven water oxidation. Phys. Chem. Chem. Phys. 2013, 15 (9), 3273-3278. DOI: 10.1039/C2CP44577H (14) Su, J.; Guo, L.; Bao, N.; Grimes, C. A., Nanostructured WO3/BiVO4 heterojunction films for efficient photoelectrochemical water splitting. Nano Lett. 2011, 11 (5), 1928-1933. DOI: 10.1021/nl2000743 (15)

Robatjazi,

H.; Bahauddin,

S.

M.;

Doiron, C.;

Thomann,

I.,

Direct

Plasmon-Driven

Photoelectrocatalysis. Nano Lett. 2015, 15 (9), 6155-6161. DOI: 10.1021/acs.nanolett.5b02453 (16) Warren, S. C.; Thimsen, E., Plasmonic solar water splitting. Energy Environ. Sci. 2012, 5 (1), 5133-5146. DOI: 10.1039/C1EE02875H (17) Moniz, S. J.; Shevlin, S. A.; Martin, D. J.; Guo, Z.-X.; Tang, J., Visible-light driven heterojunction photocatalysts for water splitting–a critical review. Energy Environ. Sci. 2015, 8 (3), 731-759. DOI: 10.1039/C4EE03271C (18) Ye, K.-H.; Chai, Z.; Gu, J.; Yu, X.; Zhao, C.; Zhang, Y.; Mai, W., BiOI–BiVO4 photoanodes with significantly improved solar water splitting capability: p–n junction to expand solar adsorption range and


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Page 16 of 19

facilitate charge carrier dynamics. Nano Energy 2015, 18, 222-231. DOI: 10.1016/j.nanoen.2015.10.018 (19) He, Z.; Shi, Y.; Gao, C.; Wen, L.; Chen, J.; Song, S., BiOCl/BiVO4 p–n heterojunction with enhanced photocatalytic activity under visible-light irradiation. J. Phys. Chem. C 2013, 118 (1), 389-398. DOI: 10.1021/jp409598s (20) Chang, X.; Wang, T.; Zhang, P.; Zhang, J.; Li, A.; Gong, J., Enhanced Surface Reaction Kinetics and Charge Separation of p-n Heterojunction Co3O4/BiVO4 Photoanodes. J. Am. Chem. Soc. 2015, 137 (26), 8356-8359. DOI: 10.1021/jacs.5b04186 (21) Wang, W.; Huang, X.; Wu, S.; Zhou, Y.; Wang, L.; Shi, H.; Liang, Y.; Zou, B., Preparation of p–n junction Cu2O/BiVO4 heterogeneous nanostructures with enhanced visible-light photocatalytic activity. Appl. Catal. B 2013, 134, 293-301. DOI: 10.1016/j.apcatb.2013.01.013 (22) Cao, X.; Tan, C.; Zhang, X.; Zhao, W.; Zhang, H., Solution-Processed Two-Dimensional Metal Dichalcogenide-Based Nanomaterials for Energy Storage and Conversion. Adv. Mater. 2016, 28, 61676196. DOI: 10.1002/adma.201504833 (23) Opoku, F.; Govender, K. K.; van Sittert, C. G. C. E.; Govender, P. P., Role of MoS2 and WS2 monolayers on photocatalytic hydrogen production and the pollutant degradation of monoclinic BiVO4: a first-principles study. New J. Chem. 2017, 41 (20), 11701-11713. DOI: 10.1039/C7NJ02340E (24) Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F., Atomically Thin MoS2: A New Direct-Gap Semiconductor. Phys. Rev. Lett. 2010, 105 (13). DOI: 10.1103/PhysRevLett.105.136805 (25) Pi, Y.; Li, Z.; Xu, D.; Liu, J.; Li, Y.; Zhang, F.; Zhang, G.; Peng, W.; Fan, X., 1T-Phase MoS2 Nanosheets on TiO2 Nanorod Arrays: 3D Photoanode with Extraordinary Catalytic Performance. ACS Sustainable Chem. Eng. 2017, 5 (6), 5175-5182. DOI: 10.1021/acssuschemeng.7b00518 (26) Pesci, F. M.; Sokolikova, M. S.; Grotta, C.; Sherrell, P. C.; Reale, F.; Sharda, K.; Ni, N.; Palczynski, P.; Mattevi, C., MoS2/WS2 Heterojunction for Photoelectrochemical Water Oxidation. ACS Catal. 2017, 7 (8), 4990-4998. DOI: 10.1021/acscatal.7b01517 (27) Li, H.; Yu, K.; Lei, X.; Guo, B.; Fu, H.; Zhu, Z., Hydrothermal Synthesis of Novel MoS2/BiVO4 Hetero-Nanoflowers with Enhanced Photocatalytic Activity and a Mechanism Investigation. J. Phys. Chem. C 2015, 119 (39), 22681-22689. DOI: 10.1021/acs.jpcc.5b06729 (28) Zhao, W.; Liu, Y.; Wei, Z.; Yang, S.; He, H.; Sun, C., Fabrication of a novel p–n heterojunction photocatalyst n-BiVO4@p-MoS2 with core–shell structure and its excellent visible-light photocatalytic reduction and oxidation activities. Appl. Catal. B 2016, 185, 242-252. DOI: 10.1016/j.apcatb.2015.12.023 (29) Yang, W.; Xiong, Y.; Zou, L.; Zou, Z.; Li, D.; Mi, Q.; Wang, Y.; Yang, H., Plasmonic Pd Nanoparticleand Plasmonic Pd Nanorod-Decorated BiVO4 Electrodes with Enhanced Photoelectrochemical Water Splitting Efficiency Across Visible-NIR Region. Nanoscale Res. Lett. 2016, 11 (1), 283. DOI: 10.1186/s11671-016-1492-8 (30) Xu, Z.; Lin, Y.; Yin, M.; Zhang, H.; Cheng, C.; Lu, L.; Xue, X.; Fan, H. J.; Chen, X.; Li, D., Understanding the Enhancement Mechanisms of Surface Plasmon-Mediated Photoelectrochemical Electrodes: A Case Study on Au Nanoparticle Decorated TiO2 Nanotubes. Adv. Mater. Interfaces 2015, 2 (13), 1500169. DOI: 10.1002/admi.201500169 (31) Cushing, S. K.; Li, J.; Meng, F.; Senty, T. R.; Suri, S.; Zhi, M.; Li, M.; Bristow, A. D.; Wu, N., Photocatalytic activity enhanced by plasmonic resonant energy transfer from metal to semiconductor. J. Am. Chem. Soc. 2012, 134 (36), 15033-15041. DOI: 10.1021/ja305603t


16

Page 17 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27


(32) Jiang, R.; Li, B.; Fang, C.; Wang, J., Metal/Semiconductor hybrid nanostructures for plasmon-enhanced applications. Adv. Mater. 2014, 26 (31), 5274-5309. DOI: 10.1002/adma.201400203 (33) Xiong, Y.; Ren, M.; Li, D.; Lin, B.; Zou, L.; Wang, Y.; Zheng, H.; Zou, Z.; Zhou, Y.; Ding, Y.; Wang, Z.; Dai, L.; Yang, H., Boosting electrocatalytic activities of plasmonic metallic nanostructures by tuning the kinetic pre-exponential factor. J. Catal. 2017, 354, 160-168. DOI: 10.1016/j.jcat.2017.08.024 (34) Ruditskiy, A.; Xia, Y., Toward the Synthesis of Sub-15 nm Ag Nanocubes with Sharp Corners and Edges: The Roles of Heterogeneous Nucleation and Surface Capping. J. Am. Chem. Soc. 2016, 138 (9), 3161-3167. DOI: 10.1021/jacs.5b13163 (35) Voiry, D.; Fullon, R.; Yang, J.; Castro e Silva, C. d. C.; Kappera, R.; Bozkurt, I.; Kaplan, D.; Lagos, M. J.; Batson, P. E.; Gupta, G.; Mohite, A. D.; Dong, L.; Er, D.; Shenoy, V. B.; Asefa, T.; Chhowalla, M., The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen. Nat. Mater. 2016, 15 (9), 1003-1009. DOI: 10.1038/nmat4660 (36) Ye, K.-H.; Wang, Z.; Gu, J.; Xiao, S.; Yuan, Y.; Zhu, Y.; Zhang, Y.; Mai, W.; Yang, S., Carbon quantum dots as a visible light sensitizer to significantly increase the solar water splitting performance of bismuth vanadate photoanodes. Energy Environ. Sci. 2017, 10 (3), 772-779. DOI: 10.1039/C6EE03442J (37) Chen, Z.; Dinh, H. N.; Miller, E., Photoelectrochemical water splitting. SpringerBriefs in Energy, New York 2013, chaper 2, pp 7-16. DOI: 10.1007/978-1-4614-8298-7 (38) Wang, S.; Chen, P.; Yun, J. H.; Hu, Y.; Wang, L., An Electrochemically Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting. Angew. Chem. Int. Ed. 2017, 56 (29), 8500-8504. DOI: 10.1002/ange.201703491 (39) Li, H.; Sun, Y.; Cai, B.; Gan, S.; Han, D.; Niu, L.; Wu, T., Hierarchically Z-scheme photocatalyst of Ag@AgCl decorated on BiVO4 (040) with enhancing photoelectrochemical and photocatalytic performance. Appl. Catal. B 2015, 170-171, 206-214. DOI: 10.1016/j.apcatb.2015.01.043 (40) Zhao, Z.; Li, Z.; Zou, Z., Electronic structure and optical properties of monoclinic clinobisvanite BiVO4. Phys. Chem. Chem. Phys. 2011, 13 (10), 4746-4753. DOI: 10.1039/C0CP01871F (41) Zhang, Z.; Yates, J. T., Jr., Band bending in semiconductors: chemical and physical consequences at surfaces and interfaces. Chem Rev 2012, 112 (10), 5520-5551. DOI: 10.1021/cr3000626

28 29


17


For Table of Contents (TOC) Graphic Use Only

1

2 3 4 5

Page 18 of 19

Synopsis: BiVO4-based electrodes have been a research hotspot for photoelectrochemical water splitting to generate storable hydrogen energy from sustainable solar energy


18

Page 19 of 19 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


BiVO4-based electrodes have been a research hotspot for photoelectrochemical water splitting to generate storable hydrogen energy from sustainable solar energy 294x115mm (150 x 150 DPI)


Boosting Charge Separation and Transfer by Plasmon-Enhanced

Recommend Documents