1

Recent Progress of Photocatalytic Water Splitting and Preliminary Work

Zhibin LeiSupervisor: Prof. Can Li

Jan. 13, 2003

State Key laboratory of Catalysis, Dalian Institute of Chemical Physics

☻ Significance of hydrogen energy

☻ Mechanism of photocatalytic water

splitting

☻ Recent development of water splitting

☻ My preliminary work and next plan

Content

3

The concentration change of CO2 in air during the past one thousand years

Significance of hydrogen energy

4

1996 1997 1998 1999 2000 20010

500

1000

1500

2000

2500

3000

3500

4000

Year

The funds used for the hydrogen project of USA in the past six years

5

我国未来所需氢的预测结果（万吨）

项 目 2010 2020 2050

合成氨 768 936.2 936.2

炼油厂加氢精制 773.1 1141.7 1141.7

燃料电池电动车 326.6 967 8758.4

燃料电池发电 73.2 216.7 1962.8

合 计 1939.1 3261.6 12799.1

6Predict hydrogen source in the next fifty years

每年投射到地面上的太阳能约 1.05×1018kWh ，相当于 1.3×106 亿吨标准煤

• Energy source• Environment• Economy

PhotocatalystH2O H2 + ½ O2

hv

A.Fijishima and K.Honda. Nature. 1972, 238, 37.

TiO2 + 2 hv 2 e–+2 h+ (1) (at the TiO2 electrode)

2 H+ + 2 e– H2 (2) (at the Pt electrode)

H2O + 2 h+ 1/2 O2 + 2 H+ (3) (at the TiO2 electrode)

H2O + 2 hv 1/2 O2 + H2 (4) (overall reaction)

Mechanism of photocatalytic water splitting

9

PtH+

H2

hv

H2O

O2

h+

e-

VB

CB

RuO2

Schematic Water oxidation and reduction process over photocatalyst

10

h+

e-

VB

CB H+/H2

O2/H2O

2

1

0

-1

E vs NHE(pH=0)

0 V

1.23 Vbadgap

The relationship between the redox potential of H2O and the VB-CB of the semiconductor

11

e-

e-

e-+h+

h+

h+H+

H2

H2O

O2

CB

VBh+

e-

hvhv

Schematic photoexicitation process in semiconductor

12

300 400 500 600 700 800 900 1000

0.0

0.5

1.0

1.5re

lati

ve in

tens

ity

(a.u

.)

Wavelengthen / nm

Solar energy distribution detected at PM 12 in Japan

13Vis 400-700nm

UV <400nm

IR >700nm

14

O2p

N2p

M nd

CB

VB

S3p

Energy level diagram of transition metal oxide, nitride and sulfide

15UV-Vis diffuse reflection spectra for Sm2Ti2O7 and Sm2Ti2S2O5

A. Ishikawa et al, J. Am. Chem. Soc., 2002, 124, 13547.

Recent development of water splitting

16

A. Ishikawa et al, J. Am. Chem. Soc., 2002, 124, 13547.

Time course of O2 evolution from Sm2Ti2S2O5 and CdS under visible light irridiation (Condition catalyst: 0.2g, La2O3, 0.2g, 0.0

1M AgNO3 solution 200ml)

17

A. Ishikawa et al, J. Am. Chem. Soc., 2002, 124, 13547.

Time course of H2 evolution from 1.0 wt %Pt- Sm2Ti2S2O5 under visible light irradiation( > 440nm, catalyst, 0.2g; solution volume, 200ml)

0.01M Na2SO3

+ 0.01M Na2S

20ml CH3OH +180ml H2O

18

A. Ishikawa et al, J. Am. Chem. Soc., 2002, 124, 13547.

Estimated band position of Sm2Ti2S2O5 at pH = 0 and 8

19

A. Kudo et al, Chem. Comm., 2002, 1958.

Diffuse reflection spectra of AgInZn7S9 (a), ZnS (b) and AgInS2 (c).

AgInS2AgInZn7S9ZnS

20

A. Kudo et al, Chem. Comm., 2002, 1958.

Photocatalytic H2 evolution over AgInZn7S9(a) and 3wt%-Pt /AgInZn7S9 under visible light irradiation(>420nm, catalyst, 0.3g; 0.25 M K2SO3- 0.35 M Na2S solution 300 ml.

21　 The set up for photocatalytic water splitting

My preliminary work and next plan

22

0 2000 4000 6000 8000 100000.0

0.5

1.0

1.5

2.0

2.5

3.0

S<9120A

mou

nt o

f H

2 / m

ol

Area

Low yield part (S<9120) hydrogen evolution standard curve for System-1 and System-2(S-1, S-2)

Y = 2.60E-4*X+0. 29

R = 0.99676

23

0 20 40 60 80 100 120 140 160

0

50

100

150

200

250

300

9120<S<1400000A

mou

nt o

f H

2 / m

ol

Area / X 10000

Middle yield part (9120<S<1400000) hydrogen evolution standard curve for S-1 and S-2

Y = 1.92-4*X+2.31

R = 0.99978

24

Y = 3.18E-4*X-159.6

R = 0.99787

0 400 800 1200 1600 20000

1000

2000

3000

4000

5000

6000

7000

S>1400000A

mou

nt o

f H

2 / m

ol

Area / X 10000

High yield part (S>1400000) hydrogen evolution standard curve for S-1 and S-2

25

0 200 400 600 800 1000 1200 1400 16000

500

1000

1500

2000

2500

3000A

mo

un

t o

f O

2 / m

ol

Area

Y = 1.92E-3*X-2.63

R = 0.99951

Oxygen evolution standard curve for S-1 and S-2

26

0 200 400 600 800 1000 1200 1400 16000

500

1000

1500

2000

2500

3000

3500

4000A

mo

un

t o

f N

2 /

mo

l

Area / X1000

Y =2.56E-3*X-3.50

R = 0.99951

Nitrogen evolution standard curve for S-1 and S-2

27

0 5 10 15 20 25

0

40

80

120

160

200

B

Am

ou

nt

of

O2

/ m

ol

Time / hours

0 5 10 15 20 25

5

10

15

20

25

30

35

A

Am

ou

nt

of

H2

/ m

ol

Time / hours

Time course of H2(A) and O2(B) evolution over CdO-360 (condition catalyst, 0.5g; 300W xenon lamp)

CH3OH 30ml,

H2O 170ml 0.01M AgNO3

200ml, >420nm

28

0 2 4 6 8 10 12 14 16 18

0

20

40

60

80

100

120

140

500

600

360

400

Am

ou

nt

of

O2

evo

luti

on

/ m

ol

Time / hours

Photocatalytic O2 evolution over CdO calcinated at varying te

mperature(Condition: catalyst 0.5g, 0.01M AgNO3 200ml)

29

0 5 10 15 20 25 30 35 40 45 50

0

50

100

150

200

250

300

350

400

450

CdO-400+La2O

3

CdO-400Am

ou

nt

of

O2

/ m

ol

Time / hours

Effect of La2O3 on the activity of the CdO calcinated at 400°C

30

0 10 20 30 40 50

0

100

200

300

400

Am

ou

nt

of

O2

/ m

ol

Time / hours

CdO-500-la2O3

CdO-400-la2O3

Photocatalytic O2 evolution over CdO calcinated at 400 and 500

C(Condition: catalyst 0.5g; 0.01M AgNO3 200ml; la2O3, 0.2g)

31

0 5 10 15 20 25 30 35 40 45 50

0

50

100

150

200

250

300

350

400

CdO-400-La2O

3

1% RuO2-CdO-400A

mo

un

t o

f O

2 /

mo

l

Time / hours

Photocatalytic O2 evolution over CdO-400 and 1% RuO2 loaded Cd

O-400(Condition: catalyst 0.5g; 0.01M AgNO3 200ml; La2O3, 0.2g)

32

0 5 10 15 20 25 30

0

50

100

150

200

250

300

350

Am

ou

nt

of

O2

/ m

ol

Time / hours

Photocatalytic O2 evolution over CdO calcinated at 400°C (Co

ndition: catalyst 0.5g, 0.01M AgNO3 200ml, La2O3 0.2g)

R = 11.2mol/h

33

0 5 10 15 20 25 30

0

40

80

120

160

200

240

3%-RuO2-(CdO-500)

2%-RuO2-(CdO-500)

CdO-500

Am

ou

nt

of

O2

/ m

ol

Time / hours

Photocatalytic O2 evolution over CdO-500 and RuO2 loaded CdO-5

00(Condition: catalyst 0.5g; 0.01M AgNO3 200ml; La2O3, 0.2g)

34

200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

AB

S

wavelengthen / nm

B C D

Uv-Vis diffuse reflection spectra for CdO prepared

at different temperature

360400500

35

10 20 30 40 50 60 700

100

200

300

400In

ten

sity

(a.

u.)

degree / 2

XRD pattern of CdO calcinated at 360C

36

200 300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

Inte

ns

ity

(a.u

.)

wavelengthen / nm

CdIn2S4 CdS

UV-Vis diffuse reflection spectra for CdS and CdIn2S4 pre

pared by the solvothermal method.

37

10 20 30 40 50 60 70

0

200

400

600

800

1000

1200

1400

1600

1800

2000

CdIn2S

4-2

CdIn2S

4-1

Inte

nsit

y

/ degree

XRD pattern of CdIn2S4 prepared by solvothermal method

38

Next Plans

1 To investigate the influence of other electron acceptor such as Fe3+ and its concentration on the activity of CdO system.

2 To explore how the different loading species with varying amount will influence the O2 evolution.

3 To synthesize Cr or Ni doped CdO to enhance the position of VB of CdO.

4 To synthesize other sulfide with better activity.