Development and Optimization of Cost Effective …...Development and Optimization of Cost Effective Material Systems For Photoelectrochemical Hydrogen Production Eric W. McFarland

Development and Optimization of Cost Effective Material Systems For Photoelectrochemical Hydrogen Production

Eric W. McFarlandDepartment of Chemical EngineeringUniversity of California, Santa Barbara

May 19, 2009

Project ID # PDP_01_McFarland

This presentation does not contain any proprietary, confidential, or otherwise restricted information

Overview

• Start date September 1, 2004• End date May 31, 2010• 90% Complete

• Total project funding– DOE share $ 894k – Contractor share $ 223k

• Funding for FY08 $498k• Funding for FY09 $0

Timeline

Budget

BarriersTechnical Barriers Addressed

• (Y) Materials Efficiency• (Z) Materials Durability• (AA) PEC Device• (AB) Bulk Material Synthesis

Technical Targets2013 DOE PEC

• Solar-to-Hydrogen Conversion Efficiency >8%– Bandgap ~ 1.7-2.2 eV

• Lifetime > 1000 hours UCSB

• Scalable to produce hydrogen at a cost less than PV-electrolysis

RelevanceThere are no known material systems that are sufficiently efficient, inexpensive, and massively

scalable that might realistically be used for the large scale, cost-effective production of hydrogen, or any chemical fuel, from sunlight.

• Task #1. With a focus on abundant and non-toxic elements, develop improved materials for solar photon absorption using high throughput methods and new syntheses.

• Task #2. Utilize high-throughput screening to identify candidate materials with a threshold efficiency and stability that , with optimization, might meet the DOE performance and stability targets.

• Task #3. Explore the effects of morphology on the PEC material system efficiency making use of nanostructures to minimize charge carrier path lengths and maximize reactive surface area.

• Task #4. Explore processing and synthesis parameters to optimize efficiency through increased conductivity and minimized charge trapping and surface recombination of selected materials.

• Task #5. Identify and minimize electrokinetic limits by synthesis of appropriate electrocatalysts compatible with the host, electrolyte, and reactant/product properties.

• Task #6. Develop a complete, “photoelectrochemical unit”, combining material absorption, charge transport, stability, and electrokinetic design features.

• Tasks #7, #8, and #9: Evaluate conceptual model reactor systems, theoretical and practical economic potential of alternative redox reactions, estimate hydrogen production costs.

Objectives and Tasks for Total Project

New Candidate Material Discovery: High Throughput

Synthesis and ScreeningAbsorption Edge

< 2.2 eV ?

Synthesis ofOptimal Compositions

and StructuresSolar Photon-electron Current

Conversion Efficiency> 10%

Solar/HydrogenEfficiency

> 8% @ 10000 hours

Processing, Surface, Electrolyte, and

Electrokinetic Optimization

Optimized Large Scale Reactor System Techno-economics

Hydrogen Cost Estimate

< $5/Kg

Yes

No

Yes

No

Yes

No

YesSuccess!

No

20 nm20 nm

Approach/Selection Criteria

Material-Class SynopsisIron Oxide

FeFeFe

FeFeFe

Spin allowede- conduction

Conduction within (001) planes is 4 order of magnitude higher than parallel to [001].

Spin forbiddene- conduction

Bandgap ~ 2 eV (40% solar light absorption).Abundant and inexpensiveHigh Stability in Electrolytes (pH>3)

Carrier TransportValence Band EdgeWater Oxidation Kinetics

Low optical absorption

promise challenges

•23 different dopant species have been tested (MxFe2-xO3)•XPS only detected Fe3+ for all samples (Pt, Cr, Mo)• No (catalytic) Pt0 observed near the surface• Pt4+ , Mo6+, Cr4+ enhance the photo-electrochemical performance •No phase segregation was observed by XRD

Doped Fe2O3

Technical Accomplishments and ProgressNew materials.

• Theory Guided Synthesis of Doped and Mixed Oxides.• Comparison of high-throughput syntheses and screening directly with theory

provides basis for additional syntheses (proposed Al and mixed donor/acceptors).

DFT calculations performed by Y. Yan et. al. through

NREL collaboration initiated in 2008

Pure Pt doped iron oxide

FY2007-2008 work

Variable Concentrations of Al Doped α-Fe2O3

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8-0.8

0.0

0.8

1.7

2.5

3.3

Ph

otoc

urre

nt (m

A/c

m2 )

Voltage vs. Ag/AgCl

0% Al in electrodeposited bath 2% Al in electrodeposited bath 6% Al in electrodeposited bath 20% Al in electrodeposited bath 40% Al in electrodeposited bath

400 450 500 550 6000.0

2.0

4.0

6.0

8.0

10.0

IP

CE

(%)

Wavelength (nm)

0 V vs Ag/AgCl--0%Al 0.2 V vs Ag/AgCl--0% Al 0.4 V vs Ag/AgCl--0% Al 0 V vs Ag/AgCl--10% Al 0.2 V vs Ag/AgCl--10% Al 0.4 V vs Ag/AgCl--10% Al

0 10 20 30 400

2

4

6

8

10

% (Al/(Al+Fe)) in Electrolyte

% (A

l/(A

l+Fe

)) in

sam

ple

• Best performance obtained ~0.3 -0.5% Al doping

• Higher % Al phase segregation to the surface

• Iso- valent doping improvement due to lattice contraction (predicted by

NREL collaborators)


N2

N2

Fe(CO)5

Ti precursor

O2Heater/T Controller

Substrate 350‐400 °CFTO

Ti:Fe2O3

Electrochemical synthesis of Ti:Fe2O3films were disappointing, new water-free synthesis route developed, 3x improvement in IPCE.


350 400 450 500 550 600 65002468

101214161820

IPC

E

Wavelength (nm)

0.2 V vs Ag/AgCl 0.4 V vs Ag/AgCl

200 300 400 500 600 700 800

Ordered mesoporous Fe2O3 Fe2O3 from Fe(NO3)3.9H2O decomposition Worm-hole mesoporous Fe2O3

Abs

orba

nce

(a.u

.)Wavelength (nm)

Worm-hole mesoporous Mesoporous Hematite

30 40 50 60 70

Ordered mesoporous hematite worm-hole mesoporous hematite

Inte

nsity

(a.u

.)

2 Theta (deg.)

Generalized syntheses developed for high surface area PEC materials: reduced overpotential for the same photon flux;

High pore volume: capability of heterogeneous nanoparticles, e.g. Pt, Au NPs

Both nanoparticles and mesoporous nanoparticles have high surface area and short transport length

Indirect direct bandgap transition due to wall effects

Ordered mesoporous

Technical Accomplishments and ProgressNew Morphologies

Hybrid PEC “Nanoreactors” - semiconductor/metal/oxide heterostructuresLow cost, scalable, solution phase synthesis of: co-catalyst/SC@encapsulant

Broadly applicablesynthesis route

Co-catalyst• Pt, Au, Ag, Pd, etc.• Virtually any nanoparticle

Support• Fe2O3, TiO2, ZnO, SiO2,

Al2O3, CeO2• Any metal oxide

Encapsulant• SiO2, ZrO2, TiO2, Al2O3Au

SiO2

Fe2O3

30 nm SiO2 10 nm SiO2 6 nm SiO2

Electrocatalystprotrusion

Au/α-Fe2O3@SiO2 FY2007-2008 work

Technical Accomplishments and ProgressComplete PEC “Systems”

•Hematite nanocubes synthesized•Pt nanoparticle electrocatalysts deposited by

photoreduction.•SiO2 encapsulated for stability.• Hydrogen production efficiency under

evaluation.

Technical Accomplishments and ProgressNew Morphologies

350 400 450 500 550 600

0

2

4

6

8

10

12Zero bias

NaOH Glucose Fructose Inositol

IPC

E (%

)

Wavelength (nm)0 20 40 60 80 100 120

-1400

-1200

-1000

-800

-600

-400

-200

0

200

Zero Bias

Phot

ocur

rent

(μA/

cm2 )

Time (s)

NaOH Sucrose Myo-Inositol Galactose Maltose Lactose Cellobiose Fructose Glucose

Technical Accomplishments and ProgressImproved Electro‐kinetics: Alternative Oxidants

•Probes efficiency in absence of ORR•??? Hematite below HER• Eliminates large ORR overpotential.•Municipal wastewater and biomass

potential feedstocks

Zero bias

1 M NaOH + 0.02 M Poly alcohol 1 Sun

350 400 450 500 550 6000

2

4

6

8

10

12

14

16

18Zero Bias

NaOH Glycerol Erythritol Xylitol

IPC

E (%

)

Wavelength (nm)

•Poly-alcohols showed an increased performance as compared to methanol•Increased IPCE ~ 17 % was achieved with Xylitol•Increased in performance could be obtained if better OER catalyst could be found•H2 production and byproducts of redox reaction to be studied

Technical Accomplishments and ProgressImproved Electro‐kinetics: Alternative Oxidants on Ti doped Fe2O3

• 3B group have direct band gap.• Effective masses are small, so

conduction should be better.• Alloying group 3A and 3B could be

used to reduce the band gap• Many possible substitutions for the

R group in CuRO2Possibly abundant and inexpensive

Stability under illuminationHigh recombination ratesValence and conduction Band positionWater Oxidation Kinetics

promise challenges

Cu+

O2-

Cr3+

Material-Class SynopsisCu Delafossites

CuLaO2

Inspired byDFT results from

NREL, M. Huda et al

Technology & Barriers:

Barrier Challenges Strengths

Y.MaterialsEfficiency

Due to the instability of Cu+ under ambient conditions, photogenerated holes are easily trapped by the Cu+ , which leads to the decomposition of the structure and decrease of the e-/h+ transport efficiency.

A narrow bandgap (~1.3 eV) makes the delafossiteabsorb most of visible light. Doping of divalent ions, e.g. Mg2+, will significantly further increase the electron conductivity.

Z.MaterialsDurability

Stability of CuCrO2 (bulk and mesoporous) under illumination in strong base solution suffers from its decomposition into spinel CuCr2O4 and dissolution of copper ions into solution.

The doping with Mg2+ significantly increase the electron conductivity in the crystals by a factor of ~1000 upon a doping of 5%. The Mg2+ doped mesoporous CuCrO2 has been shown to be stable under a long time illumination (159 hours) from the results of TEM and XPS.

AA. PEC Device and System Auxiliary Material.

Synthesis of mesoporous delafossite structure has some limitation in extending to other materials beside CuCrO2 due to the reaction of metal ions with silica template at high temperature. Further research into less expensive nanoparticles, applicable to other delafossite structures, is also a major key issue.

The silica template applied in the synthesis produced mesoporous nanoparticles with a high surface area , thin wall thickness, and reltivelygood crystallization. The nanocasting method can be applied in the synthesis of CuLaO2, CuGaO2, CuFeO2, and their sulfide and selenides.

AB.BulkMaterialsSynthesis

The obtained material powder is rough and difficult to be redispered in the electrolyte.

Materials are inexpensive and easy to synthesize.

Mesoporous CuCrO2 delafossite structures, SA=90 m2/g

30 40 50 60 70 80

200

400

600

800

1000

1200

1400

1600

1800

Inte

nsity

(a.u

.)

2 θ (degree)

(a) N2 adsorption/desorption isotherm (b) pore size distribution

• Hydrogen production demonstrated under visible illumination in powders, quantification in progress.

• High conductivity, Doping with Mg2+

increases conductivity by a factor of 1000

• Indirect bandgap ~1.3 eV


400 600 800 1000 1200

0.2

0.4

0.6

0.8

1.0

Bulk CuCrO2

Mesoporous Mg:CuCrO2

Mesoporous CuCrO2

Abs

orba

nce

(%)

Wavelength (nm)

Mesoporous CuCrO2 delafossite structures show activity for hydrogen production in Na2S + NaOH electrolyte

1020

3040

5002468

10

12

14

16

18

Bulk MesopCuCrO2 MesopMgCuCrO2

H2 e

volu

tion

μL/h

Illumination hours

Hydrogen production rate of bulk, mesoporous CuCrO2, and Mg2+ doped mesoporous CuCrO2 (5 mg powder in 15 mL NaOH and Na2S solution). Mesoporous delafossite shows an efficiency > x10 bulk material, however, λ < 400nm, required.

Bulk CuCrO2CuCrO2Mg: CuCrO2


Active for H2

Not active for H2

3

0

2

4

6

8

10

12

0.5 3

16.5 19 59

61.5

121.5

123

125.5

146.5

149

3

5

1H2 evolution uL/h

I = 8 mW/cm2

I = 20 mW/cm2

Bulk Mesoporous CuCrO2

Mesoporous Mg: CuCrO2

Cu metal nanorod

Mg doped CuCrO2 shows the highest chemical stability over 149 hours of illumination.

Became nanoparticles

Photocorrosion: MesoporousCuCrO2 delafossite structures


Cu+ oxidized into Cu2+ according to XPS, such reaction is proposed:2CuCrO2+ H2O CuCr2O4+CuO + H2

970 960 950 940 930 9203000

4000

5000

6000

Inte

nsity

(a.u

.)

Binding energy (eV)

CPS_CuCrO2_0h_Cu/2 CPS_CuCrO2_2h_Cu/8 CPS_CuCr2O4_0h_Cu/14

Cu 2p3/2

Cu 2p1/2

XPS results on Photo-oxidation of Cu+ in bulk and mesoporous delafossite structures

XPS of control and illuminated delafossiteI‐1: Mg:CuCrO2, remained 100% Cu(II) I‐2: Mesoporous CuCrO2, remained 58%I‐3: Bulk CuCrO2, remained 0%

02468

I‐1 I‐2 I‐3

H2 evolution from 5 mg CuCrO2 18.5 hours (uL/h)

100% 58% 0%


Stability for Cu(II) Cu(I)Cu (I) Cu(II )

CuLaO2 CuGaO2• Recent success in synthesisof several new Delafossites, though not all pure phase materials.

• Have set-up necessary systems to rapidly create other combinations in the same class.

• PEC performance screening in progress. CuFeO2


CuLaO2 +La2O3CuLaO2 +La2O3

CuGaS2SnS • Recent success in synthesisof new sulfides.

• H2S furnace able to process safely multiple samples.

• PEC performance screening in progress.


CuGaS2

CuGaSe2

CuGaSe2

20 40 60 80300

350

400

450

500

550

600

650

Inte

nsity

(a.u

.)

2 Θ

WSe2

WSe2

2 0 3 0 4 0 5 0 6 0 7 0 8 00

2 0 0

4 0 0

6 0 0

Inte

nsity

(a.u

.)

2 Θ

C u In S e 2

Mesoporous CuInSe2

• Recent success in synthesisof new selenides by wet

chemical route amenable to scale-up.

• PEC performance screening in progress.


Mesoporous CuCr2O4 spinel structures active as powders for hydrogen production in Na2S + NaOH electrolyte only under UV illumination

1.0 1.5 2.0 2.5

Inte

nsity

(a.u

.)

2 θ (degree)

(a)

20 30 40 50 60 70

Inte

nsity

2 θ (degree)

(b)


Mesoporous CuCr2O4 spinel active as powders for hydrogen production in Na2S + NaOH electrolyte only under UV illumination

Electrodeposition of NiFe Electrocatalysts

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8-3

-2

-1

0

1

2

3

4

5 Fe

2O

3 Control

Fe2O

3 Ni(II)-Fe(III)

Fe2O3 Ni(II)-Fe(II) Fe2O3 Ni(II)

Cur

rent

Den

sity

(mA

/cm

2 )

Applied Voltage (vs Ag/AgCl)

(a)

Sample

mV onset vs Ag/AgCl

αIo [A/cm2]α

Fe2O3 Control 650 0.68 2.1-E7

NiFe (III) 560 0.59 7.4E-7

NiFe (II) 490 0.39 2.0E-7

Ni 490 0.44 2.1E-7

0 40 80 120 160-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

Cur

rent

Den

isty

(mA

/cm

2 )

Time (s)

α-Fe2O3 Control α-Fe2O3 Td=90 S α-Fe2O3 Td=30 S α-Fe2O3 Td=120 S α-Fe2O3 Td=60 S

(c)

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8-2

-1

0

1

2

3

4

5

-0.4 -0.2 0.0-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Applied Voltage (vs Ag/AgCl)

Cur

rent

Den

sity

(mA/

cm2 )

Fe2O3 Control Fe2O3 Ni(II)-Fe(III)

(b)

•NiFe(III) improved the PEC performance by as much as 4.5 times as compared to the control sample.•NiFe(II) and Ni had a decrease in the PEC performance•The optimum loading for the NiFe(III) electrocatalyst corresponded Tdep ~90 sec.

Electrochem. Comm. 2009 (in Press)

Technical Accomplishments and ProgressImproved Electro-kinetics

0.5 1.0 1.5 2.0 2.5

0.0

1.2

2.5

3.7

Cur

rent

Den

sity

(mA

/cm

2 )

Applied bias vs Ag/AgCl

WO3

WO3- RuO2 micells0.33 M H3PO4

100 mW/cm2

•WO3 is greatly hindered by Oxygen Evolution reaction (a)•Fe2O3 is greatly improved by NiFe or RuO2 electrocatalyst deposition•No improvement observed by: RuO2 nanoparticles deposition on WO3(c) or electrocatalyst deposition on Fe2O3 (d)

a) b)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.0

1.0

2.0

3.0

4.0

Cur

rent

Den

sity

(mA

/cm

2 )

Applied Bias Vs Ag/AgCl

Fe2O3

Fe2O3 25% Ni Micells Fe2O3 50% Ni Micells Fe2O3 75% Ni Micells Fe2O3 100% Ni Micells Fe2O3 RuO2 Micells

1M NaOH

c) d)

0.8 1.2 1.6 2.0 2.4

0.0

0.2

0.4

0.6

0.8

1.0

Applied Bias (vs Ag/AgCl)

Cur

rent

(mA

)

FTO FTO- RuO2

WO3 no catalyst0.33M H3PO4 Ar degassed

-0.2 0.0 0.2 0.4 0.6 0.8

0.0

1.0

2.0

3.0

4.0

Applied Bias Vs Ag/AgCl

Cur

rent

Den

sity

(mA

/cm

2 )

Fe2O3

Fe2O3 25% Ni Micells Fe2O3 50% Ni Micells Fe2O3 75% Ni Micells Fe2O3 100% Ni Micells Fe2O3 RuO2 Micells

1M NaOH

Dark IV curves

PEC performance

Technical Accomplishments and ProgressImproved Electro‐kinetics

Electronegative surface species shifts conduction bandElectrons energy relative to H2/H+ redox level

0 1000 2000 3000

-900-800-700-600-500-400-300-200-100

0

iv

iii

ii

Phot

ocur

rent

(μA

/cm

2 )

Time (s)

i

i: Ti-doped sample without CoF3 treatment in NaOH solution

ii: Ti-doped sample with CoF3 treatment in NaOH solution

iii: Ti-doped sample without CoF3 treatment in NaOH+Glucose solution

iv: Ti-doped sample with CoF3 treatment in NaOH+Glucose solution

•Record efficiency for a True Zero bias hematite photoelectrode•New method applicable to Fe2O3 to shift the VB/CB

Chem. Comm. 2009 (in press)

Technical Accomplishments and ProgressProcessing and synthesis

Summary• New PEC Materials

– Theory guided synthesis and characterization of additional doped iron oxides supports theoretical predictions that the Mott‐Insulator symmetries must be broken to improve conductivity. HTE of Al doped hematite identified 0.3‐0.5 % as optimal, IPCE increased 4‐5x over controls . Initial results of donor/acceptor doping predicted by theory, disappointing.

– Theory inspired synthesis and initial characterization of new, CuMO2 Delafossites completed for M=Cr,Fe,Ga,La. Now attempting electrode configurations.

– Several new oxides (CuCr2O4 ), sulfides (SnS, CuGaS2), and selenides (WSe2,CuInSe2 , CuGaSe2 ) synthesized, PEC characterization in progress.

• Optimization of Material Performance– Surface modification with F to shift conduction band‐edge of Ti‐doped hematite

produced record zero bias (two electrode) efficiency for hematite ~ 1% at 450 nm.

– NiFe electrocatalysts have shown an improvement of ~ 4X on the performance

– Biomass analogues have been successfully photo decomposed with increased performance 15 times or higher than NaOH.

• New Structures– Developed generalized synthesis routes to integrated absorber/catalyst/coating PEC

systems. Will defer further work to focus on new absorber material identification.

Future Work(focus on finding and optimizing solar spectrum absorber consisting of earth abundant materials)

• Synthesis and Screening of New Materials:– Iron based oxides (to make go/no‐go decision on iron oxides in 2009)

• High‐throughput investigation of Fe‐Ti up to 40% Ti.• Thin‐Film doped iron oxides using organometallic pyrolysis (Si, Ti,C, doping guided by theory)

– Copper based oxides• Complete screening of delafossite oxides materials

– Attempt pure phase Cu(Fe)O2 , Cu(La)O2– Delafossite synthesis as films to allow electrochemical analysis.

– Begin initial exploration of Sulfides, Phosphides, and Selenides• Solution synthesis of Cu(Ga)Se2 , Cu(La)S2 , SnS , WSe2 , SnP• Develop High‐Throughput Synthesis Methods.

– High‐throughput screening and selected physical, electronic, and photoelectrochemical characterization of new host materials. Quantitative analysis of photocurrents and photovoltages and indirect measurement of hydrogen production activity and flatband potential. Selected use of Mott‐Schottky analysis and direct bulk H2 yields.

– Detailed analysis of selected candidates including carrier lifetime analysis by femtosecond transient absorption spectroscopy; internal quantum efficiency (IQE) characterization, and Raman.

• New Structures– Thin films and Mesoporous supports (ITO, WO3, TiO2) with nanometer scale doped iron oxide inclusions. – Solution phase synthesis of p‐n junctions, Cu(M)O2 /TiO2

30

Collaborations

• DOE H2 Program

– Directed Technologies (Participated in PEC System Analysis)

– Standard PEC testing group discussion

– Yanfa Yan, NREL (Theoretical Calculations)

– Eric Miller, University of Hawaii (Electrocatalysts for WO3)

– Clemens Heske, UNLV (Characterization of Fe2O3)

– Tom Jaramillo, Stanford (round‐robin testing)

• M. Gräztel, Ecole polytechnique fédérale de Lausanne ( Fe2O3 )

Documents

Development and Optimization of Cost Effective …...Development and Optimization of Cost Effective Material Systems For Photoelectrochemical Hydrogen Production Eric W. McFarland