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Hydrogen production from water with solar energy
Kazunari Domen
Chemical Systems Engineering
The University of Tokyo
2008.3.14
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
GIES2008
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
H2 + 1―2
O2 ΔG0 = 238 kJmol-1H2Ohν
Hydrogen Production from Water using Solar Energy
▪ Solar cell + Electrolysis: pilot plants
▪ Photoelectrochemical Cell: good efficiencies with tandem cells
Efficiency=12.4 %
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
Efficiency=18.3 %J. A. Turner et al., Science 1998, S. Licht et al., J. Phys. Chem. B 2000,
Two examples of photoelectrochemical cells
Photoelectrochemical cells + PV
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
solar energy conversion efficiency = 3~4%
M. Grätzel, Nature 2001, 414, 338–344.
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
▪ Solar cell + Electrolysis
▪ Photoelectrochemical Cell
H2 + 1―2
O2 ΔG0 = 238 kJmol-1H2Ohν
▪ Artificial Photosynthesis (Photocatalysis)Inorganic solid materialmetal complexorganic materialbiomaterial
▪ Photosynthesis
Available photons for water splitting
H2O → H2 + 1/2O2
ΔG0 = 237 kJ/mol= n×F ×E0
= 2×96500 C/mol×1.23 V
One electron energy = 1.23 eV
λ=1000 nm1.23 eV )(nmλ
ν 1238h (eV) E ==Photon energy
0 500 1000 1500 2000Wavelength λ/nm
0
1.5
3R
adia
tion
Pow
er k
Wm
-2μm
-1
UV Vis IR
Solar Energy Distribution
1.23 eV =1000 nm
Solar Energy Conversion Efficiency
Solar energy conversion efficiency(Q.E.=100 %)
33.5
29.4
25.1
20.6
16.2
11.9
7.95
4.29
1.67
Energy efficiency/ %
800
750
700
650
600
550
500
450
400
Wavelength/ nm
SEM Images of La-doped NaTaO3
0.1 µm
Prof. A. Kudo (Tokyo Univ. Sci.)
Overall water splitting on NiO(0.2wt%)/NaTaO3 :La
200W Xe-Hg Lamp
Layered photocatalyst
BG:4.1eVQY:50% (270nm)
Prof. A. Kudo (Tokyo Univ. Sci.)
Time Course of Overall Water Splitting on NiO(0.2wt%)/NaTaO3:La
Q.E. = 56 %
Challenge with Visible Light
H2 + 1―2
O2 ΔG0 = 238 kJmol-1H2O
Photocatalytic Materials with
・Sufficient Solar Energy (Visible Light) Absorption
・Potential for Overall Water Splitting・Enough Stability
?
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
GaN:ZnO solid solution
GaN GaN:ZnO ZnO
1 μm
RuO2 : 3.5 wt%
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
0 5 10 15 20 25 30 350
0.5
1.0
1.5
2.0
Am
ount
of e
volv
ed g
ases
/ m
mol
Reaction time / h
Evac.▼
H2
O2
N2
Magnetic stirrer
Water cooling
450 W high pressure Hg lamp
NaNO2 aq.
Catalyst: 0.3 gCocat.: Rh 1 wt%, Cr 1.5 wt%Reactant soln.: 370 mL (pH 4.5)Inner irradiation type cell with a 2 M NaNO2 aq. filter450 W Hg lamp
Catalyst: 0.3 gCocat.: Rh 1 wt%, Cr 1.5 wt%Reactant soln.: 370 mL (pH 4.5)Inner irradiation type cell with a 2 M NaNO2 aq. filter450 W Hg lamp
λ > 400 nmλ > 400 nm
Visible Light-Driven Overall Water Splitting on Rh-Cr oxide/GaN:ZnO
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
30 nm
SEM image TEM image
Rh-Cr mixed oxide
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
Electron micrographs of Rh-Cr oxide/GaN:ZnO
hνe-
h+
H+H2
H2OO2
Overall water splitting on Rh-Cr oxide/GaN:ZnO
λ > 300 nmλ > 300 nm
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
Q.E. of overall water splitting on Rh-Cr oxide/GaN:ZnO
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
300 350 400 450 5000
0.51.01.52.02.53.03.54.04.5
Q
uant
um e
ffici
ency
/ %
Wavelength / nmA
bsor
banc
e /
a.u.
Q.E.
RuO2-loaded(Q.E. 0.23%)
5.9 %
Two approaches for overall water splitting
H+ / H2
O2 / H2O
Red
Oxhν
H+
H2
H2O
O2h+
e–
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
One-step excitation
e–
h+
h+
e–
H2 evolution
O2 evolution
H+
H2
H2O
O2
hν
hν
Two-step excitation(Z-scheme)
Oxide
BaTaO
2 N
CaTaO
2 N
SrTaO2 N
Ta3 N
5
LaTaON
2
CaLaTiO
N
LaTiO2 N
Li2 LaTa2 O
6 N
Various Oxynitrides
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
e-
e- H+
H2
h+
h+
I-
IO3-
e-
e-
e-
e-
H2O
O2
hν
hν
Pt/WO3
Pt/TaON
Two-step overall water splitting under visible light
(Reaction conditions)Pt/TaON: 0.2 g + Pt/WO3: 0.2 g5 mM-NaI aqueous solution: 250 mL (pH = 6.5)300 W Xe-lamp, L-42 cut-off filter
200
150
100
50
02520151050
H2
O2
N2
Chem. Commun. 2005, 3829
Time / hA
mou
nt o
f evo
lved
gas
es / μm
ol
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
(λ < 450 nm)(λ < 500 nm)
70
60
50
40
30
20
10
020151050
Time / h
Am
ount
of e
volv
ed g
ases
/ μm
ol
H2
O2
N2
λ > 420nm
Two-step overall water splitting on Pt/WO3+Pt/BaTaO2N
e-
e- H+
H2
h+
h+
I–
IO3–
e-
e-
e-
e-
H2O
O2
hν
hν
Pt/BaTaO2N
Pt/WO3
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
(λ < 450 nm)
(λ < 670 nm)
4
3
2
1
0
K-M
func
tion
(a.u
.)
800700600500400300Wavelength / nm
Ta3N5(O2 evolution)BaTaO2N(H2 evolution)
BaNbO2N
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
Available materials for two-step overall water splitting
Application of oxynitrides to PEC cell
(H+/H2)0
1.23(O2/H2O)
V.B.O2p + N2p
C.B. Ta5d
E.G. = 2.5 eV
+2.2
-0.3-
+
Potential / V vs NHE at pH0
OTaN
oxynitride TaON
K. Domen et al., J. Phys. Chem. B, 2003, 107, 1798
R. Abe et al., Chem. Commun., 2005, 3829
TaON electrode
e–
Visible lightH2 O2
Pt electrode
薄膜電極化
阿部(北海道大学)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Cur
rent
den
sity
/ m
A c
m-2
1.00.80.60.40.20.0-0.2-0.4Potential / V vs. Ag/AgCl
(a) as-prepared TaON (b) treated with TaCl5 (c) treated with NH3
e-
e-
e-
e-
e-
e-
TaCl5-calcination
Ta2O5 fine particles
TaON fine particles
NH3-treatment
phase boundaries
[Conditions]Supporting electrolyte: 0.1 mol-L-1 of Na2SO4Potentiostat: PARSTAT 2263Rate of scan: 50 mV / sLight source: Xe illuminator (300 W, 300 < λ < 500 nm)
[Conditions]Supporting electrolyte: 0.1 mol-L-1 of Na2SO4Potentiostat: PARSTAT 2263Rate of scan: 50 mV / sLight source: Xe illuminator (300 W, 300 < λ < 500 nm)
Potential(V vs. NHE)
o- 0.3
+ 0.5
Ta 5d
W 5d
O2p + N2p
O2p
2.6 eV
2.5 eV
1.5
1.0
0.5
0.0
Cur
rent
den
sity
/ m
A c
m-2
0.80.40.0-0.4Potential / V vs. Ag/AgCl
WO3 TaON
Cell 1Rh-Cr/GaN:ZnO
Cell 2Pt/WO3
20 mmol L-1 NaI aq. 500 mL300 W Xe lamp (λ > 300 nm)
1200
1000
800
600
400
200
0403020100
H2 O2
300
250
200
150
100
50
0403020100
H2 O2
Time / h
Cell 1
Cell 2
Am
ount
of g
as e
volv
ed / μm
olA
mou
nt o
f gas
evo
lved
/ μm
ol
IO3−
IO3−
I−H2O
OO22
e− h+h+e− I−
HH22
HH++
IO3−
WO3TaON
Two-room overall water splitting
Overall water splitting with sacrificial reagents
H2O H2 + 1/2O2
2H2O + Na2S H2 + S + 2NaOH
H2O + CH3OH 3H2 + CO2
6H2O + C6H12O6 12H2 + 6CO2
ΔG0 = 238 kJmol-1
TEM image of stratified CdSTEM image of stratified CdS
CdS capsules (30 nm) consist of nanoparticles (5nm)
Prof. K. Tohji (Tohoku Univ.)
H2 production on stratified CdS from Na2S solution
Prof. K. Tohji (Tohoku Univ.)
Chemical System EngineerinChemical System EngineerinThe University of Tokyo
▪ Solar cell + Electrolysis
▪ Photoelectrochemical Cellvs
▪ Artificial Photosynthesis (Photocatalysis)
materials
Key IssuesNew materials
Application to wide area; Reactor designHybridization; structure
Hydrogen Production from Water using Solar Energy