Solar Water Splitting: Photocatalyst Materials Discovery and Systems

Development

Thomas F. McNultyGE Global Research

May 23, 2005

Project ID # PDP34This presentation does not contain any proprietary or confidential information

Overview

2GEThomas F McNultyMay 23, 2005ID # PDP34

• Anticipated July 1, 2005 start• December 31, 2007 completion

Usable semiconductor bandgap:Materials Development

• Materials Efficiency• Materials Durability• Bulk Materials Synthesis

Systems Development• Systems Design and Evaluation

• $3.75MM total – $3.0MM DoE– $750k GE/Caltech

• $1.25MM FY05

Budget

Barriers

CaltechPartners

Timeline

Objectives

Program Objectives:• Development of Photoelectrochemical system exhibiting:

– 9% Solar to hydrogen efficiency– > 10,000 hrs durability– < $5.00 gge hydrogen costs

Program Objectives:• Development of Photoelectrochemical system exhibiting:

– 9% Solar to hydrogen efficiency– > 10,000 hrs durability– < $5.00 gge hydrogen costs

3GEThomas F McNultyMay 23, 2005ID # PDP34

FY05 Objectives:• Increased materials efficiency through band-gap engineering

– Valence band modification through anionic doping of oxides– Optimization of composition through high-throughput screening (HTS)– Optimization of particle morphology for cell design/manufacture

• Development of robust membrane technology

FY05 Objectives:• Increased materials efficiency through band-gap engineering

– Valence band modification through anionic doping of oxides– Optimization of composition through high-throughput screening (HTS)– Optimization of particle morphology for cell design/manufacture

• Development of robust membrane technology

Background

173

1% 5% 10% 15%

$66.48

$5.54

$5.54 $5.54$5.54$6.65$13.30

$4.43

1091 / 1110185 / 188Singapore

1305 / 1620221 / 275Honolulu

Production rate* kg/day

Average insolation in Jan / Jul (W/m2/hr)

Location

1369 / 1898229 / 317Phoenix

1148 / 1748195 / 296L.A.

634 / 1500112.5 / 254Albany

247.5 / 113242 / 192Ankorage

1091 / 1110185 / 188Singapore

1305 / 1620221 / 275Honolulu

Production rate* kg/day

Average insolation in Jan / Jul (W/m2/hr)

Location

1369 / 1898229 / 317Phoenix

1148 / 1748195 / 296L.A.

634 / 1500112.5 / 254Albany

247.5 / 113242 / 192Ankorage

*assumes 10% efficiency

PanelsBOS

1734.5 11.515 acres22 acres46 acres

229 acres

• System cost / efficiency critical technology drivers• Performance regional

• System cost / efficiency critical technology drivers• Performance regional

Example: 1000 kg/day remote refueling station in Albany, NY

4GEThomas F McNultyMay 23, 2005ID # PDP34

Concept

Photoelectrochemical element

O2 H2

Photoelectrochemical element

O2 H2

Advantages:• reduced cost• greater materials flexibility• H2 formed separately from O2

Advantages:• reduced cost• greater materials flexibility• H2 formed separately from O2

5GEThomas F McNultyMay 23, 2005ID # PDP34

Approach

H+/H2

H2O/O2

TiO

2, E g=

3.2

eV

KT a

O3,

E g= 3

. 5 e

V

S rT i

O3,

Eg=

3.7

eV

4.0

5.0

6.0

7.0

8.0

Ener

gy (r

el. v

ac. L

evel

)

Bi 2O

3, E g=

2.9

eV

P bO

, Eg=

2.8

eV

WO

3, E g=

2.7

eV

Valence band energy level attributed to O2p Mxdtransition

Position of valence/conduction bands vs. H2O redox

• Solar efficiency of oxides limited by VB position• Anionic substitution offers potential of reducing VB energy level

• Solar efficiency of oxides limited by VB position• Anionic substitution offers potential of reducing VB energy level

6GEThomas F McNultyMay 23, 2005ID # PDP34

Approach

• Anionic doping of TiO2 shown to reduce overall band-gap

• Conduction band effects not reported

• TiO2-xNx and TiO2-xCx not optimized

• Other systems (e.g. SrTiO3, KTaO3 not reported

• Long-term stability unknown

• Anionic doping of TiO2 shown to reduce overall band-gap

• Conduction band effects not reported

• TiO2-xNx and TiO2-xCx not optimized

• Other systems (e.g. SrTiO3, KTaO3 not reported

• Long-term stability unknown

Asahi et.al., Science, 293 (2001) 269-271

Kung et.al., Science, 297 (2002) 2243-2245

7GEThomas F McNultyMay 23, 2005ID # PDP34

Approach

• HTS demonstrated as useful technique to measure effects of compositional perturbation

• HTS coupled with reactive sputtering deposition to optimize concentration of nitrogen/carbon substitution

• HTS demonstrated as useful technique to measure effects of compositional perturbation

• HTS coupled with reactive sputtering deposition to optimize concentration of nitrogen/carbon substitution

8GEThomas F McNultyMay 23, 2005ID # PDP34

Technical ProgressCompositional optimization by HTS:

X

Y

• X-Y stage allows 48 samples to be sputtered sequentially

• Each sample can be sputtered at different N/Ar flow ratio varying from 0 to 20 vol%.

• Electronic circuitry fabricated directly on top of each sample

• Direct photoelectrochemicalmeasurement.

• X-Y stage allows 48 samples to be sputtered sequentially

• Each sample can be sputtered at different N/Ar flow ratio varying from 0 to 20 vol%.

• Electronic circuitry fabricated directly on top of each sample

• Direct photoelectrochemicalmeasurement.

Sputter ControlInterface

9GEThomas F McNultyMay 23, 2005ID # PDP34

Technical Progress

10GEThomas F McNultyMay 23, 2005ID # PDP34

Absorption vs. Wavelength

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

200 300 400 500 600 700 800

wavelength (nm)

abso

rptio

n (a

rb. u

nits

)

SrTiO3-xNx As-synthesized SrTiO3

SrTiO3-xNx As-synthesized SrTiO3

• Nitrogen substitution leads to absorbance state at lower energy

• Nitrogen substitution leads to absorbance state at lower energy

Valence band modification:

C as aXPS (This s tr ing can be edit ed in Cas aXP S.DEF/Pr in tF oot Not e. txt )

N1 1

N1

x 101

225

230

235

240

402 400 398 396 394 392 390Binding Energy (eV)

Technical Progress

11GEThomas F McNultyMay 23, 2005ID # PDP34

Photoanode O2

Quartz window

NorylGasket

Ag/AgCl Reference

Pt Cathode H2

hv

Photoelectrochemical cell:

• Modular• Split-cell, membrane cell, particulate capability• Upgradeable

• Modular• Split-cell, membrane cell, particulate capability• Upgradeable

Future Work

12GEThomas F McNultyMay 23, 2005ID # PDP34

• High throughput screening:– 48 sample thin-film array with individually-addressable cells for dopant optimization– nitrogen, carbon doping of oxides

• Powder optimization:– Optimization of powder morphology for incorporation into membranes– Bulk synthesis of powders identified in HTS– VB, CB measurements by UPS

• Membrane development:– Processing optimization– Characterization / optimization of surface morphology– Membrane-based photoelectrochemical testing