Photoelectrochemical Hydrogen Production Using New Combinatorial Chemistry Derived Materials

Eric W. McFarland (PI), University of California, Santa Barbara DOE Hydrogen Program DE-FC36-01GO11092

Primary Objective:Discovery of efficient, practical, and economically sensible newmaterials for photoelectrochemical production of hydrogen from water and sunlight.

Methodology:Apply combinatorial methods to complement the traditional research paradigm of serial “deductive” chemical research with a deliberate, high-speed, “inductive” exploration of the composition-structure-property relationships of new metal-oxide based solid-state materials.

May 2003 Merit Review and Peer Evaluation

Photovoltaic+

Materials “Issues”•Electrodes

•Electrocatalytic Activity•Stability•Conductivity

•Solar Cell•Bandgap•Energetics•Synthesis route

Cathode2H+ +2e- =>

H2

AnodeH2O =>

2H+ +2e- + 1/2O2

Electrolysis

Photoelectrocatalyst

Materials “Issues”• Absorbance• Transport e-/h+• Surface Electrocatalysis• Band Structure Energetics• Stability and Cost Bulk Particulates

Structural Photoelectrodes~

Combinatorial Approach: Paradigm Shift

Library Design:Diversity in Composition

- dopants in known hosts- new hosts- surface electrocatalysts

Diversity in Synthesis- structure variability- surfactant templates

Rapid Synthesis and Processing:Electrochemical DepositionElectroless DepositionParallel Reactor BlocksRapid Serial Scanning CellsPyrolysis

High-Throughput Screening:PhotoelectrochemicalChemo-Optical

Detailed AnalysisOf Lead Materials

Relevance:• The materials will be active electrocatalysts stable in electrolytes.

– Dual use applications in electrolysers and fuel cells.

• They will have efficient solar spectrum absorbance and efficientelectron/hole conduction properties.

– Dual use in photovoltaic applications.

• May be economically incorporated in reactor designs using photoelectrodes or bulk slurry particulates.

– Dual use in environmental photocatalysis.

• New metal oxide materials developed in this program will be inexpensive in bulk quantities.⇒ Primary Use In Cost Competitive Large Scale Hydrogen

Production

Materials Developed As Part of This Research Have Broad Applications In the US Energy Program

Project Timeline (Start Date September 2001)

Sept. 04Sept. 01 Sept. 02 Sept. 03System(s):

Automated Electrodeposition (Task Y1-1)Automated Pyrolysis

Electro-Optical Screening (Task Y1-5)Electrochemical Screening (Task Y1-3)

Optical Band Gap Screening (Y2-4)

Synthesis :

Electroless WOMxO

Validation Libraries - ZnO (Task Y1-4)AxByCzO Libraries (TaskY1- 6)

Heterostructure Libraries (Task Y2- 6)Mesoporous Libraries (TaskY1- 7)

Electrocatalysis Libraries (Y2-3)

Generalized Synthesis Chemistry (Task Y1-2)ZnO (Y2-2)

AxByCzO Libraries (Y2- 1)

Mesoporous Libraries (Y2- 7)Electrocatalysis Libraries (Y3)

ZnO (Y3)AxByCzO Libraries (Y3)

Mesoporous Libraries (Y3)

Screening and Detailed Quantitative Analysis:Validation Libraries (Task Y1-4, 9)

AxByCzO Libraries (Task Y1-6,9)

Electrocatalysis Libraries (Y2-3)

AxByCzO Libraries (Y2- 1)Mesoporous Libraries (Y2- 7)

Electrocatalysis Libraries (Y3)

AxByCzO Libraries (Y3)Mesoporous Libraries (Y3)

ZnO (Y2-2) ZnO (Y3)

Data Management:Database Structure (Task Y1-8)

Software and Data Implementation

Outreach and Tech Transfer:Adrena Inc/SBA Materials

IEA Annex 14Research Publications - 10 published papers

2 Patent Applications (mesoporous MOx, Pt/WO3 Fuel Cell Cat)

Significant Results To Date

• Design and fabrication of combinatorial chemistry systems for synthesis and screening of hydrogen producing photocatalysts.

• Demonstrated that compositional and preparative modifications of known metal oxide hosts may improve their photoelectrocatalytic properties. (WO3 with ZB visible band photolysis, ZnO:X with improved visible band absorbance and improved stability)

• First electrochemical synthesis of ordered nanoporous metal oxides (Patent Assigned to SBA Materials)

• First electroless synthesis of functional metal oxide materials and nanoporous frameworks.

• Discovery of nanoparticulate Pt/WO3 which is photoactive and resistant to CO poisoning and controlled electrosynthesis of high activity Au nanoclusters.

• Identification of H intercalation as critical component of poisoning resistance of metal oxide electrocatalysts.

Independently addressable counter electrodes

SourceMeasure

Common working electrode

Auto channel switch

D/A Board: Dig Out

Parallel Synthesis

Tasks 4 & 5: HTS bandgap measurement

OceanOpticsS2000

Spectrometer

X-Y-Z MotionStages

(computer controlled)

Oriel 1kWXe Lamp

Integrating spherefor diffuse reflectance

CombinatorialLibrary

Generalized Synthesis Chemistries

1. MO Depositionelectrode: 2 H2O + 2 e

- H2 + 2(OH– )sur

[Mn+

(ligand)] + n(OH– )sur M(OH)nligands (acidic) = peroxide

(basic) = lactate, citrate, ethylene glycol, acetate

2. Dehydration/AnnealM(OH)n MOn/2 + n/2 H2O

Aqueous: M+ MOH MO

Non-Aqueous: M+ + O2 MO

Metal deposition/Oxidation Metal Oxide DepositionM+ M MO

1. Metal ElectrodepositionM

n++n e- M

o (Cathodic)

2. Anodization/AnnealM

o+ H2O MO + 2 H

++ 2 e –

Mo

+ O2 MO

1. Direct MO DepositionxMn+ + y/2O2 + ne- → MxOyIn DMSO etc

Automated Spray Pyrolysis SystemFe2O3

Library

System Enclosure

X-Y Stage

Shutter plate

Hot Plate

Multiple Solutions

Nozzle

Sample

Compressed Air

Flow &Pressure Controller

TC

Multi-Valve

Controler

Pinch valve

1 meter

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

0

2

4

6

8

10

12

Light Off

Light On

Phot

ocur

rent

(µA/

cm2 )

Potential vs Pt reference(V)

WO3

Pt/WO3

Ru/WO3

Ni/WO3

Co/WO3

Cu/WO3

Zn/WO3

5%10%15%30%50%

WO3

Pt/WO3

Ru/WO3

Rh/WO3

Pd/WO3

Ag/WO3

1% 2% 3% 4% 5%

0 10 20 30 40 500

40

80

120

160

Ni/W Films Pt/W Films

Me/

W a

tom

ic R

atio

in F

ilms

Me/W mole% in Electrolyte

5030

1510

50

ZnCu

CoNi

RuPt

Metal Salt Concentration(mole%)

54

32

10 Pt

RuRh

PdAg

Metal Salt Concentration(mol%)

Task 1: Continue WO3:X - stable, cost effective host

100% W

30% Pt / W

50% Pt / W

Pure Pt

Pulse Voltage(V)-1.0 -1.5 -2.0 -3.0

0.0 0.2 0.4 0.6 0.8

Potential vs Pt Electrode(V)0.0 0.2 0.4 0.6 0.8

-1

0

1

2

3

4

5

6

7

Cur

rent

Den

sity

(mA/

cm2 )

Potential vs Pt Electrode(V)0.0 0.2 0.4 0.6 0

Potential vs Pt Electrode(V)

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

-2

0

2

3

5

6

8

Cur

rent

Den

sity

(mA/

cm2 )

Potential vs Pt reference(V)

Pure Pt

Pure WO3

MethanolOxidation

Tungsten-Molybdenum Mixed Oxides

0 20 40 60 80 10001234

15202530354045

Phot

ocur

rent

(µA/

cm2 )

[Mo]

1V bias

zero bias

WO3

W0.8Mo0.2O3

W0.7Mo0.3O3

W0.5Mo0.5O3

W0.3Mo0.7O3

W0.2Mo0.8O3

MoO3

Increasing Mo Concentration

Raman SpectroscopyXRD Patterns

20 22 24 26 28 30

MoO3

W0.2Mo0.8O3

W0.5Mo0.5O3

W0.8Mo0.2O3

WO3

Inte

nsity

(a.u

.)

2 θ500 550 600 650 700 750 800 850 900 950100010501100

MoO3

W0.2Mo0.8O3

W0.3Mo0.7O3

W0.5Mo0.5O3

W0.7Mo0.3O3W0.8Mo0.2O3WO3

Inte

nsity

(a.u

.)

Raman Shift (cm-1)

No prior reports of zerobias hydrogen evolution from WO3=> Defect(doping) by electrodeposition shift flatband

New, stable, substitutional phases discovered by electrodeposition and characterized

Superior photocatalytic oxidation properties

Significantly increased cation intercalation capacity.

Electrodeposition of nanocrystalline WO3 by pulsed deposition

Tpulse =500msec

10 1000

50100150200250300350400450500

5003

Parti

cle

Size

(nm

)

Pulse Width (msec) -0.4 -0.2 0.0 0.2 0.4-20

0

20

40

60

Normal WO3 on ITO Nano WO3 on ITO

Ph

otoc

urre

nt(A

/cm

2)

Voltage(V)-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-8

-6

-4

-2

0

2

4

6

nano WO3 (Tpulse : 5msec)

Cur

rent

den

sity

(mA/

cm2 )

for H

+ Int

erca

latio

n

Voltage vs SCE(V)

Tpulse =100msec Tpulse =50msec Tpulse =5msec1 µm 1 µm 1 µm1 µm

• S.H.Baeck, T. Jaramillo, G.D.Stucky, and E.W.McFarland,”Controlled Electrodeposition of Nanoparticulate Tungsten Oxide”, Nano Letters, 2(8), 831(2002).

Electrodeposition of Mesoporous WO3 Task: 7

50 nm 50 nm 50 nm

1 µm 1 µm

MesoporousNonporous

1 2 3 4 5 6 7

Inte

nsity

(a. u

.)

2θ (degree)

100200300

100

200 300

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

Cur

rent

Den

sity

(mA/

cm2 m

g of

WO

3)

Voltage vs Ag/AgCl Reference Electrode (V)-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-1.20

-1.00

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

Cur

rent

Den

sity

(mA/

cm2 m

g of

WO

3)

Voltage vs Ag/Agcl Reference Electrode (V)

Hydrogen Intercalation

0 20 40 60 80 100 1200

4

8

12

16

20

24

Phot

ocur

rent

(mA/

cm2 m

g)

Time (s)

Mesoporous

Nonporous

Lamellar Structure with 25Å wall thickness and 15Åinterlayer spacing

Accepted and in Pres Adv. Materials 2003

Zerobias Photocurrent

Mesoporous WO3 Library with SDSSDS Concentration (wt%)

0 1 2 3 4 5Deposition V

- 0.5

- 0.8

- 1.0

- 1.5 -0.5 V

-1.5 V -0.8 V-1.0 V

• Electrically active by design

• No requirement of post treatment

• Particle size & Density can be controlled by deposition condition

• Post treatment (Removal of Polymer)

• Doping density limitation (monolayer)

• Broad particle size distribution

• Non-uniform Dispersion

Electrodeposition of Nanoparticles

S. H. Baeck, Thomas F. Jaramillo, E.W.McFarland, Proc. ACS (2003)

50nm

• Uniform Dispersion

• Narrow Particle size distribution

• Particle size & Density can be controlled by template

Block copolymer micelle encapsulation / Dip Coating

Thomas F. Jaramillo, S. H. Baeck, B. Roldan Cuenya, E.W.McFarland, JACS (2003) In Press

Advantage

Disadvantage

50nm

0 100 200 300 400-6.0

-5.5

-5.0

-4.5

-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

Cur

rent

(mA/

cm2 )

Time (sec)

As-deposited After calcination 300 deg. C, 2 hrs

Unfortunate3 eV Bandgap, minimal

visible light photocurrent

UVcut-offfilter

PromisingPhotocatalyticallyactive (in the UV)

UnacceptablePhotocurrent decay from photoanodic

corrosion

Inexpensive in bulkHigh conductivityHigh Dopant Solubility

Approach#1: Introduce dopants to improve visible absorption

Task 2: Zinc Oxide Photocatalyst Host

A B C D

All depositions:200mM Zn(NO3)2 in DMSO (no saturated O2)except Fe row (100mM ZnCl2) -1.16V vs. Ag pseudo-reference (-1.0 vs. Ag/AgCl)85 deg. C15min deposition onto ITO-coated glass substrate

1

2

3

4

Fe(NO3)2

CrCl3

MnCl2

NiCl2

0%

0%

0%

0%

0.6%

2.9%

1.0% 1.5%

5.7% 8.3%

2.9% 5.7% 8.3%

2.9% 5.7% 8.3%

Other Transition metal doped ZnO library: Fe, Cr, Mn, Ni

Mn improves ZnO stability.Ni improves ZnO photoactivity in the UVFe may increase photoactivity in the visibleTo date best is Co which improves both.

0 1 2 3 4

0

100

200

300

400

500

600

700

800

Increased stability for 2.9% Mn

Phot

ocur

rent

(µA/

cm2 )

Time (min)

pure ZnO Zn(97.1%):Mn(2.9%) Zn(94.3%):Mn(5.7%) Zn(91.7%):Mn(8.3%)

0 1 2 3 40

200

400

600

800

1000

1200

1400

Increased photoactivity forall Ni-doped samples

Phot

ocur

rent

(µA/

cm2 )

Time (min)

pure ZnO Zn(97.1%):Ni(2.9%) Zn(94.3%):Ni(5.7%) Zn(91.7%):Ni(8.3%)

Communication and Cooperative Efforts: Task 8Internal:Strong collaborations with the laboratory of Professor Galen Stucky and UCSB Materials Research

Laboratory (NSF)External:Frequent academic and industrial presentations.Participant in the IEA Hydrogen Production Task Committee.Cooperation with SBA Materials, Inc. and the Cycad Group, Inc. exploring issues related to process economics

for commercialization of photoelectrocatalysis and photoelectroxidation. Licensing of Patents.

Publications Resulting from DOE Hydrogen Program Funding (Sept. 01-Present):1) “High-Throughput Screening System for Catalytic Hydrogen-Producing Materials,” J. Combinatorial Chem. 4 (1) 17-22 (2002).2) “Combinatorial Electrochemical Synthesis and Characterization of Tungsten-Molybdenum Mixed Oxides,” Korean J. Chem. Engin. 19 (4) 593-596 (2002).3) “Combinatorial Electrochemical Synthesis and Characterization of Tungsten-based Mixed Metal Oxides,” J. Combi. Chem. Vol 4( 6) 563-568 (2002).4) “Controlled Electrodeposition of Nanoparticulate Tungsten Oxide,” Nanoletters 2 (8) 831-834 (2002).5) “Influence of Composition and Morphology on Photo and Electrocatalytic Activity of Electrodeposited Pt/WO3,” Am.Chem.Soc., Abs.Pap. 224: 062-FUEL

Part 1 (2002)6) “Photoelectrochemical Hydrogen Production Using New Combinatorial Chemistry Derived Materials,” (2002) Proceedings of the 2002, DOE Hydrogen

Program Review NREL/CP-610-324057) “A Cu2O/TiO2 Heterojunction Thin Film Cathode for Photoelectrocatalysis,” Solar Energy Materials. Vol. 77, 3,229-237 (2003).8) “Electrochemical Synthesis of Nanostructured ZnO films Utilizing Self Assembly of Surfactant Molecules at Solid-Liquid Interfaces,” J. Am. Chem. Soc.

124(42); 12402-12403 (2002)9) “Electrocatalytic Properties of Thin Mesoporous Platinum Films Synthesized Utilizing Potential-Controlled Surfactant Assembly,” Advanced Materials.

(Accepted and in press 2003).10) "Catalytic Activity of Supported Au Nanoparticles Deposited From Block Co-polymer Micelles“, (Accepted and in Press 2003, J. Am. Chem. Soc. )11) “Enhancement of Photocatalytic and Electrochromic Properties of Electrochemically Fabricated Mesoporous WO3 Thin Films”, Submitted Adv.

Materials 200312)"Synthesis of Tungsten Oxide on Copper Surfaces by Electroless Deposition" Submitted Chem. Mater. (2003).

Education:Students - Tom Jaramillo, Anna Ivanovskaya, Alan KleinmanPost-Doctoral Associates – Dr. Sung-Hyeon Baeck, Dr. Kyoung-Shin ChoiVisiting Scholars – Professor Withana Siripala

Generalized Synthesis ChemistriesCommunication and Cooperative Efforts: Task 8