Nanocomposite Photocatalysts for Solar Hydrogen Production
Hydrogen Economy
Carbon Economy
Jae Sung Lee
Pohang University of Science and Technology
POSTECH
Dept. of Chemical Engineering
Photocatalytic
PhotocatalyticHydrogen
HydrogenProduction
Production
Photocatalyst
Photocatalyst
POSTECH
Dept. of Chemical Engineering
Sunlight
Sunlightfor
forHydrogen
HydrogenProduction
Production
Photoelectrochemical
Photoelectrochemical
(PEC)
(PEC)Cell
Cell
PV
PV/Electrolysis
/Electrolysis
Photocatalysis
Photocatalysis
Sun
Photocatalysts
e-
hυ
H2
O2
S.C.
H2O
O2
H2
O2
Pt
H2O
No need for H2/O2 separation
High efficiency
Low stability
Fabrication cost
POSTECH
Dept. of Chemical Engineering
hυ H2
Low cost
Low efficiency at present
Photocatalytic
PhotocatalyticWater
WaterSplitting
Splittingby
byParticulate
ParticulatePhotocatalysts
Photocatalysts
C.B
e-
hv≥Eg
V.B
e-++
he-
e
H+ Photocatalytic- Water Reduction
2H+ + 2e → H2
H2
hv or heat
Recombination !!
h+
O2
Photocatalytic Water OxidationH2O
H2O + 2h+ → ½O2 + 2H+
Low Quantum Yield !
Low Photo-Activity !
Photocatalytic Overall Water Splitting
H2O + hv → H2 + ½O2
POSTECH
Dept. of Chemical Engineering
(E = -1.23eV)
Overall
OverallWater
WaterSplitting
Splittingunder
underUV
UVlight
light
Q.Y.
Q.Y.==
2× number of hydrogen molecules (or 4× number of oxygen molecules)
Number of photons abosorbed
H. G. Kim et al., Chem. Comm., 1077-1078 (1999)
D. W. Hwang et al., J. Catal., 193, 40-48 (2000)
J. Kim, Chem. Comm., 2488-2489 (2002)
D. W. Hwang et al., J. Phys. Chem., 109(6), 2093-2102 (2005)
POSTECH
1%
1%
TiO2
(1972)
SrTiO3
(1982)
POSTECH
Dept. of Chemical Engineering
10%
10%
30%
30% 23%
23%
35%
35%
50%
50%
50%
50%
K4Nb6O17 K2La2Ti3O10 Sr2Nb2O7 Ba-La2Ti2O7 Ba-Sr2Nb2O7 La/NaTaO2
(2003)
(2003)
(2002)
(1999)
(1986)
(1997)
Domen
Domen
Kudo
Solar
SolarLight
Light Spectrum
Spectrum
Sun
0%
0.5
%
3.5
%
46%
38%
17%
Wavelength (nm)
UV
VIS
600 nm
1008 nm
1.59eV
3.26eV
POSTECH
Dept. of Chemical Engineering
IR
2.07eV
1.23eV
Band
BandGaps
Gapsand
andBand
BandPositions
Positions
Two Requirements for Band Structure:
E
(eV)
NHE
(V)
-3.5
-1.0
-4.5
0.0
-5.5
+1.0
-6.5
+2.0
-7.5
+3.0
-8.5
+4.0
1.
Band gap: 1.6 eV < Eg < 3.0eV
2.
Band positions
SiC
(n,p)
GaP
(n,p)
GaAs
(n,p)
CdS
CdSe (n)
(n)
TiO2
(n)
ZnO
(n) Fe2O3 In2O3
SnO
(n) (n) WO (n) 2
3
(n)
H2O/O2
1.4eV
2.3eV 1.7eV
2.4eV
3.0eV
2.2eV
3.2eV
2.7eV
2.8eV
3.2eV
3.8eV
POSTECH
Dept. of Chemical Engineering
H+/H2
(S2-/S)
(@pH=1)
Search
Searchfor
forthe
theVisible
VisibleLight
LightPhotocatalysts
Photocatalysts
1. New Single Phase Materials
1.1.New
NewSingle
SinglePhase
PhaseMaterials
Materials
2.2.Photosensitizer
Photosensitizer(PS)
(PS)
2. Photosensitizer (PS)
3.3.Modification
ModificationofofUV
UVPhotocatalysts
Photocatalysts
- -Cation
CationDoping
Doping
- -Anion
AnionDoping
Doping(Nitrides,
(Nitrides,Carbides,
Carbides,Sulfides)
Sulfides)
4.4.Composite
CompositePhotocatalysts
Photocatalysts
5.5.Solid
SolidSolution
Solution
5. Solid Solution
3. Modification
Control of band
position
A
Energy
CB
(Visible light)
VB
λ(nm)
(Wide BG)
POSTECH
Dept. of Chemical Engineering
(Narrow BG)
4. Composite Photocatalysts
AANovel
NovelUndoped,
Undoped,Single
Singlephase,
phase,
Photocatalyst,
Photocatalyst,PbBi
PbBi22Nb
Nb22OO99
J. Am. Chem. Soc., 126(29), 8912-8913 (2004)
J. Solid State Chem., 179, 1211-1215 (2006)
A layered perovskite of
Aurivillius phase
X-ray diffraction pattern and the high-resolution TEM image of PbBi2Nb2O9
sintered at 1473K for 24h and its structure model
POSTECH
Dept. of Chemical Engineering
Optical
OpticalProperties
Properties
Absorbance (a. u.)
A : TiO2-xNx
B : PbBi2Nb2O9
(A)
(A)
(B)
200
300
400
500
600
700
800
wavelength /nm
UV-Vis
UV-VisDiffuse
DiffuseReflectance
Reflectancespectra
spectra
POSTECH
Dept. of Chemical Engineering
(B)
Water
WaterSplitting
Splittingwith
withSacrificial
SacrificialAgents
Agents(λ≥420
(λ≥420nm)
nm)
Band Gap Energy
Catalysts
Hydrogen Evolution
Oxygen Evolution
Eg(eV)
λab(nm)
μmol/gcat•hr
3Q.Y.(%)
μmol/gcat•hr
3Q.Y.(%)
PbBi2Nb2O9
2.88
431
7.6
0.95
520
29
TiO2-xNy
2.77
451
trace
0
221
14
Catalyst loaded with 1wt% Pt, 0.3g; light source, 450W W-Arc lamp(Oriel) with UV cut-off
filter(λ≥420nm). Reaction was performed in aqueous methanol solution
(methanol 30ml + distilled water 170ml) or in an aqueous AgNO3 solution(0.05mol/l, 200ml)
H2O
H2
Ag+
-
Ag0
+
CO2
CH3OH
H2 Evolution
POSTECH
Dept. of Chemical Engineering
+
O2
H2O
O2 Evolution
Band
BandGap
GapReduction
Reductionof
ofLayered
LayeredPerovskites
PerovskitesBy
ByPb
Pb&
&Bi
Bi
2H-
H2
CB
e
Bi
Nb 4d
Visible Light
Ⅹ
Nb
(≥420 nm)
O
O 2p
h+
Pb 6s
VB
O2 + 2H-
-
2OH CH3CH(OH)CH3
CO2
Fig.
O9
Fig.Total
Totaland
andpartial
partialdensity
densityofofstates
states(DOS)
(DOS)ofofPbBi
PbBi2Nb
2Nb22O
9
POSTECH
Dept. of Chemical Engineering
Pb
Strategies
Strategiesfor
forDevelopment
Developmentof
ofComposite
CompositePhotocatalysts
Photocatalysts
O.F.C
H.F.C
Layered compound
J.J.S.S.Jang
Janget.
et.al.,
al.,J.J.Catal.,
Catal.,231
231(2005)
(2005)213
213
Nanoparticles
(p-type)
Bulk Oxide
(n-type)
What
Whatfunctions
functions??
→
→Photocatalytic
Photocatalyticp-n
p-nNanodiodes
Nanodiodes(PCD)
(PCD)
How
Howtotofabricate
fabricate??
→
→Nano-Bulk
Nano-BulkComposite
Composite(NBC)
(NBC)
POSTECH
Dept. of Chemical Engineering
Photocatalytic
Photocatalyticp-n
p-nNanodidoes
Nanodidoes
Hydrothermal treatment method
: CaFe2O4
: PbBi2Nb1.9W0.1O9
p-type
CaFe2O4
150oC, 7days
n-type
PbBi2Nb1.9W0.1O9
Reactor
Reactor
PbBi
W0.1OO9 synthesized
by the solid state reaction method.
PbBi2Nb
2Nb1.9
1.9W
0.1 9 synthesized by the solid state reaction method.
CaFe
CaFe2OO4 synthesized
synthesizedby
bythe
thesol-gel
sol-gelmethod.
method.
2
4
POSTECH
Dept. of Chemical Engineering
Photocatalytic
Photocatalyticp-n
p-nNanodiodes
Nanodiodes(PCD)
(PCD)
Angew.
Angew.Chem.
Chem.Int.
Int.Ed.
Ed.44
44(2005)
(2005)4585
4585
POSTECH
Dept. of Chemical Engineering
Water
WaterSplitting
Splittingwith
withSacrificial
Sacrificialagents
agents(λ≥420
(λ≥420nm)
nm)
Catalysts
Band Gap Energy
Hydrogen Evolution
Oxygen Evolution
Eg(eV)
λab(nm)
μmol/gcat•hr
3Q.Y.(%)
μmol/gcat•hr
3Q.Y.(%)
CaFe2O4/
PbBi2Nb1.9W0.1O9
2.75
450
34.8
4.16
675
38
PbBi2Nb2O9
2.88
431
7.6
0.95
520
29
CaFe2O4
1.99
623
trace
0
trace
0
TiO2-xNy
2.77
451
trace
0
221
14
Catalyst loaded with 0.1wt% Pt, 0.3g; light source, 450W W-Arc lamp(Oriel) with UV cut-off
filter(λ≥420nm). Reaction was performed in aqueous methanol solution (methanol 30ml + distilled
water 170ml) or in an aqueous AgNO3 solution(0.05mol/l, 200ml).
POSTECH
Dept. of Chemical Engineering
Photocatalytic
Photocatalyticp-n
p-nNanodiodes
Nanodiodeswith
withan
anOhmic
OhmicJunction
Junction
Appl. Phys. Lett., 89, 064103 (2006)
WO3
(A)
W(CO)6
(B)
WO3
(D)
WO3
PbBi2Nb1.9Ti0.1O9
PbBi2Nb1.9Ti0.1O9
200 nm
W/PbBi2Nb1.9Ti0.1O9
O2
2OH-
O2 + 2H+
Flow
WO3
W metal
(C)
WO3/W/PbBi2Nb1.9Ti0.1O9
PbBi2Nb1.9Ti0.1O9
POSTECH
Dept. of Chemical Engineering
Photocatalytic
Photocatalytic HH22and
andOO22evolution
evolutionfrom
fromwater
waterunder
undervisible
visiblelight
light(λ≥420nm)
(λ≥420nm)
Catalysts
Band Gap Energy
Hydrogen Evolution
Oxygen Evolution
Eg(eV)
λab(nm)
μmol/gcat•hr
3Q.Y.(%)
μmol/gcat•hr
3Q.Y.(%)
WO3/W/
PbBi2Nb1.9Ti0.1O9
2.86
433
49.33
6.06
741
41
CaFe2O4/
PbBi2Nb1.9W0.1O9
2.75
450
34.8
4.16
675
38
PbBi2Nb2O9
2.88
431
7.6
0.95
520
29
CaFe2O4
1.99
623
trace
0
trace
0
TiO2-xNy
2.77
451
trace
0
221
14
Catalyst loaded with 0.1wt% Pt, 0.3g; light source, 450W W-Arc lamp(Oriel) with UV cut-off
filter(λ≥420nm). Reaction was performed in aqueous methanol solution (methanol 30ml + distilled
water 170ml) or in an aqueous AgNO3 solution(0.05mol/l, 200ml).
POSTECH
Dept. of Chemical Engineering
p-n
p-nNanocomposite
NanocompositePhotocatalysts
Photocatalysts--Summary
Summary
Schottky
Schottky
p-n
p-n
p-n/ohmic
p-n/ohmic
n-type
metal
CB
2H+
e-
e-
EF
H2
O2+2H+
h+
VB
2OH-
Ohmic
contact
Schottky
Schottky
Junction
Junction
One
Onephoton
photonprocess
process
+
Effective
+-e-separation
Effectivehh-e
separation
POSTECH
Dept. of Chemical Engineering
One
Onephoton
photonprocess
process
+
Effective
+-e-separation
Effectivehh-e
separation
Two
Twophoton
photonprocess
process
Higher
Highernet
netphotonenergies
photonenergieswhile
while
absorbing
long
wavelength
photons
absorbing long wavelength photons
+ - separation
Effective
+-e- separation
Effectivehh-e
Ecocat
Ecocat People
People
$$ponsors
General Motors
National Research
Laboratory
Hydrogen Energy R&D
Center (The 21st Century
Frontier R&D Program)
POSTECH
Dept. of Chemical Engineering