Hydrogen Economy - CMU · Carbon Economy Hydrogen Economy. ... PV /ElectrolysisPV /Electrolysis...
Transcript of Hydrogen Economy - CMU · Carbon Economy Hydrogen Economy. ... PV /ElectrolysisPV /Electrolysis...
POSTECHDept. of Chemical Engineering
Jae Sung LeePohang University of Science and Technology
Nanocomposite Photocatalysts for Solar Hydrogen Production
Carbon Economy
Hydrogen Economy
POSTECHDept. of Chemical Engineering
Photocatalytic Hydrogen ProductionPhotocatalytic Hydrogen Production
PhotocatalystPhotocatalyst
POSTECHDept. of Chemical Engineering
Sunlight for Hydrogen ProductionSunlight for Hydrogen Production
PV /ElectrolysisPV /Electrolysis Photoelectrochemical(PEC) Cell
Photoelectrochemical(PEC) Cell PhotocatalysisPhotocatalysis
Photocatalysts
O2H2 O2
H2hυ
Sun
No need for H2/O2 separationHigh efficiencyLow stabilityFabrication cost
Low costLow efficiency at present
e-
H2
H2OPt
O2
H2OS.C.hυ
POSTECHDept. of Chemical Engineering
Photocatalytic Water Splitting by Particulate PhotocatalystsPhotocatalytic Water Splitting by Particulate Photocatalysts
e-h+
C.B
V.Bhv≥Eg
H+
H2
H2OO2
2H+ + 2e- → H2
Photocatalytic Water Reduction
H2O + 2h+ → ½O2 + 2H+Photocatalytic Water Oxidation
H2O + hv → H2 + ½O2 (E = -1.23eV)Photocatalytic Overall Water Splitting
e-h+
Recombination !!
Low Quantum Yield !
Low Photo-Activity !
hv or heat
h+h+
e-e-
POSTECHDept. of Chemical Engineering
Overall Water Splitting under UV lightOverall Water Splitting under UV light
TiO2(1972)
1%23%23%
Sr2Nb2O7(1999)
50%50%
Ba-Sr2Nb2O7(2003)
50%50%
La/NaTaO2(2003)
35%35%
Ba-La2Ti2O7(2002)
KudoKudo
30%30%
K2La2Ti3O10(1997)
DomenDomen
SrTiO3(1982)
1% 10%10%K4Nb6O17
(1986)DomenDomen
POSTECH
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)
POSTECHDept. of Chemical Engineering
Solar Light SpectrumSolar Light Spectrum
Sun
Wavelength (nm)
UV VIS IR
3.26eV 1.59eV
2.07eV
600 nm
1.23eV
1008 nm
46% 38% 17%3.5%
0.5%
0%
POSTECHDept. of Chemical Engineering
0.0
+1.0
+2.0
+3.0
+4.0
-1.0
E NHE(eV) (V)
-4.5
-3.5
-5.5
-6.5
-7.5
-8.5
H+/H2
H2O/O2
(S2-/S)
(@pH=1)
GaAs(n,p)
1.4eV
GaP(n,p)
2.3eV
CdSe(n)
1.7eV
CdS(n)
2.4eV
SnO2(n)
3.8eV
TiO2(n)
3.2eV
ZnO(n)
3.2eV
SiC(n,p)
3.0eV
WO3(n)
2.8eV
Fe2O3(n)
2.2eV
In2O3(n)
2.7eV
Band Gaps and Band PositionsBand Gaps and Band Positions
Two Requirements for Band Structure:
1. Band gap: 1.6 eV < Eg < 3.0eV
2. Band positions
POSTECHDept. of Chemical Engineering
1. New Single Phase Materials
2. Photosensitizer (PS)
3. Modification of UV Photocatalysts
- Cation Doping
- Anion Doping (Nitrides, Carbides, Sulfides)
4. Composite Photocatalysts
5. Solid Solution
1. New Single Phase Materials
2. Photosensitizer (PS)
3. Modification of UV Photocatalysts
- Cation Doping
- Anion Doping (Nitrides, Carbides, Sulfides)
4. Composite Photocatalysts
5. Solid Solution
3. Modification
1. New Single Phase Materials 2. Photosensitizer (PS)
4. Composite Photocatalysts
λ(nm)
A
5. Solid Solution
CB
VB
Ene
rgy
(Wide BG) (Narrow BG)
(Visible light)
Control of bandposition
Search for the Visible Light PhotocatalystsSearch for the Visible Light Photocatalysts
POSTECHDept. of Chemical Engineering
X-ray diffraction pattern and the high-resolution TEM image of PbBi2Nb2O9sintered at 1473K for 24h and its structure model
A Novel Undoped, Single phase, Photocatalyst, PbBi2Nb2O9
A Novel Undoped, Single phase, Photocatalyst, PbBi2Nb2O9
J. Am. Chem. Soc., 126(29), 8912-8913 (2004)J. Solid State Chem., 179, 1211-1215 (2006)
A layered perovskite of Aurivillius phase
POSTECHDept. of Chemical Engineering
UV-Vis Diffuse Reflectance spectraUV-Vis Diffuse Reflectance spectra
(B)
(A)
Optical PropertiesOptical Properties
wavelength /nm
200 300 400 500 600 700 800
Abs
orba
nce
(a. u
.)
(A)
(B)
A : TiO2-xNxB : PbBi2Nb2O9
POSTECHDept. of Chemical Engineering
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)
142210trace4512.77TiO2-xNy
29
3Q.Y.(%)
0.95
3Q.Y.(%)
431
λab(nm)
5207.62.88PbBi2Nb2O9
μmol/gcat•hrμmol/gcat•hrEg(eV)
Oxygen EvolutionHydrogen EvolutionBand Gap EnergyCatalysts
Water Splitting with Sacrificial Agents (λ≥420 nm)Water Splitting with Sacrificial Agents (λ≥420 nm)
H2 Evolution O2 Evolution
+
-H2O
CH3OH
H2
CO2 +
-Ag+
H2O
Ag0
O2
POSTECHDept. of Chemical Engineering
Fig. Total and partial density of states (DOS) of PbBi2Nb2O9Fig. Total and partial density of states (DOS) of PbBi2Nb2O9
Bi
Pb
Nb
O
CB
VB
Nb 4d
O 2p
2H- H2
Pb 6s
CH3CH(OH)CH3
Ⅹ
2OH-O2 + 2H- CO2
Visible Light
(≥420 nm)
h+
e
Band Gap Reduction of Layered Perovskites By Pb & BiBand Gap Reduction of Layered Perovskites By Pb & Bi
POSTECHDept. of Chemical Engineering
What functions ?→ Photocatalytic p-n Nanodiodes (PCD)
How to fabricate ? → Nano-Bulk Composite (NBC)
What functions ?→ Photocatalytic p-n Nanodiodes (PCD)
How to fabricate ? → Nano-Bulk Composite (NBC)
H.F.CO.F.C
J. S. Jang et. al., J. Catal., 231 (2005) 213J. S. Jang et. al., J. Catal., 231 (2005) 213
Bulk Oxide(n-type)
Nanoparticles(p-type)
Layered compound
Strategies for Development of Composite PhotocatalystsStrategies for Development of Composite Photocatalysts
POSTECHDept. of Chemical Engineering
p-typeCaFe2O4
n-type
PbBi2Nb1.9W0.1O9
Hydrothermal treatment method
ReactorReactor
PbBi2Nb1.9W0.1O9 synthesized by the solid state reaction method.CaFe2O4 synthesized by the sol-gel method.
PbBi2Nb1.9W0.1O9 synthesized by the solid state reaction method.CaFe2O4 synthesized by the sol-gel method.
: PbBi2Nb1.9W0.1O9
: CaFe2O4
Photocatalytic p-n NanodidoesPhotocatalytic p-n Nanodidoes
150oC, 7days
POSTECHDept. of Chemical Engineering
Photocatalytic p-n Nanodiodes (PCD)Photocatalytic p-n Nanodiodes (PCD)
Angew. Chem. Int. Ed. 44 (2005) 4585Angew. Chem. Int. Ed. 44 (2005) 4585
POSTECHDept. of Chemical Engineering
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).
386754.1634.84502.75CaFe2O4/
PbBi2Nb1.9W0.1O9
142210trace4512.77TiO2-xNy
0trace 0trace6231.99CaFe2O4
29
3Q.Y.(%)
0.95
3Q.Y.(%)
431
λab(nm)
5207.62.88PbBi2Nb2O9
μmol/gcat•hrμmol/gcat•hrEg(eV)
Oxygen EvolutionHydrogen EvolutionBand Gap EnergyCatalysts
Water Splitting with Sacrificial agents (λ≥420 nm)Water Splitting with Sacrificial agents (λ≥420 nm)
POSTECHDept. of Chemical Engineering
Photocatalytic p-n Nanodiodes with an Ohmic JunctionPhotocatalytic p-n Nanodiodes with an Ohmic Junction
(D)
W(CO)6
PbBi2Nb1.9Ti0.1O9
W/PbBi2Nb1.9Ti0.1O9
WO3/W/PbBi2Nb1.9Ti0.1O9
O2Flow
2OH- O2 + 2H+
WO3
W metal
PbBi2Nb1.9Ti0.1O9
PbBi2Nb1.9Ti0.1O9
200 nm
(B)(A)
(C)
WO3
WO3
WO3
Appl. Phys. Lett., 89, 064103 (2006)
POSTECHDept. of Chemical Engineering
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).
386754.1634.84502.75CaFe2O4/
PbBi2Nb1.9W0.1O9
142210trace4512.77TiO2-xNy
0trace 0trace6231.99CaFe2O4
29
41
3Q.Y.(%)
0.95
6.06
3Q.Y.(%)
431
433
λab(nm)
5207.62.88PbBi2Nb2O9
74149.332.86WO3/W/ PbBi2Nb1.9Ti0.1O9
μmol/gcat•hrμmol/gcat•hrEg(eV)
Oxygen EvolutionHydrogen EvolutionBand Gap EnergyCatalysts
Photocatalytic H2 and O2 evolution from water under visible light (λ≥420nm)Photocatalytic H2 and O2 evolution from water under visible light (λ≥420nm)
POSTECHDept. of Chemical Engineering
p-n Nanocomposite Photocatalysts - Summaryp-n Nanocomposite Photocatalysts - Summary
EF
n-typemetal
Ohmic contact
e-
e-2H+
H2
h+ 2OH-
O2+2H+
CB
VB
SchottkySchottky p-np-n p-n/ohmicp-n/ohmic
One photon process
Effective h+-e- separation
One photon process
Effective h+-e- separationOne photon process
Effective h+-e- separation
One photon process
Effective h+-e- separation
Two photon process
Higher net photonenergies while absorbing long wavelength photons
Effective h+-e- separation
Two photon process
Higher net photonenergies while absorbing long wavelength photons
Effective h+-e- separation
Schottky
Junction
Schottky
Junction