Hydrogen Economy - CMU

POSTECHDept. of Chemical Engineering

Jae Sung LeePohang University of Science and Technology

Nanocomposite Photocatalysts for Solar Hydrogen Production

Carbon Economy

Hydrogen Economy


Photocatalytic Hydrogen ProductionPhotocatalytic Hydrogen Production

PhotocatalystPhotocatalyst


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


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-


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)


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%


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


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)


5. Solid Solution

3. Modification

1. New Single Phase Materials 2. Photosensitizer (PS)


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


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


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


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


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


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


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


Photocatalytic p-n Nanodiodes (PCD)Photocatalytic p-n Nanodiodes (PCD)

Angew. Chem. Int. Ed. 44 (2005) 4585Angew. Chem. Int. Ed. 44 (2005) 4585


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


0trace 0trace6231.99CaFe2O4

29

3Q.Y.(%)

0.95

3Q.Y.(%)

431

λab(nm)

5207.62.88PbBi2Nb2O9



Water Splitting with Sacrificial agents (λ≥420 nm)Water Splitting with Sacrificial agents (λ≥420 nm)


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)


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


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



Photocatalytic H2 and O2 evolution from water under visible light (λ≥420nm)Photocatalytic H2 and O2 evolution from water under visible light (λ≥420nm)


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


One photon process


Two photon process

Higher net photonenergies while absorbing long wavelength photons


Two photon process

Higher net photonenergies while absorbing long wavelength photons


Schottky

Junction

Schottky

Junction


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