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Solar Production of Fuels and Chemicals; is there a cost-effective path forward?

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• Big Picture

Outline

Big Picture

• Solar Energy Conversion: What Works, What Doesn’t , and Why

• Strategies and Tactics: Potentially Cost-Effective Artificial Photosynthetic Processes

• Improved Light Absorbers and Electrocatalysts

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p g y

• Beyond Water Splitting

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R di ti F Th l R ti H BRadiation From Thermonuclear Reactions Has Been And Always Will Be The Most Important Source

Of Energy For The Earth and Human Beings

Societal prosperity through the 19th century was powered by renewable biomass.

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5

4

Mtoe/year

20117 billion~ 17 TW

Prosperity + Population Demand

19122 billion people

~ 1 TW

• Societal prosperity through the 19th century was powered by renewable biomass.• Global prosperity in the 20th Century was possible due to the availability of large quantities

of inexpensive fossil hydrocarbon resources.• Global prosperity in the 22nd century will depend on availability of enormous quantities of

sustainable energy resources (32+TW) and/or significant unprecedented population control.• The 21st Century Better Figure Out How to Get Us There.

Low cost, solar derived, hydrocarbon fuels have provided unprecedented opportunities for global egalitarian

prosperity.

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$ 63,000,000,000,000~ $120/GJ

512,000,000,000 GigaJoules

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Yes, there is a limit on how much we can spend

Society can not spend (for long) more on energythan the value created

Conservation of Money

World GDP 2010 ~ $63 Trillion/y(US/Ger/China/India 14/3.6/6/1.5)

World Energy Use ~ 16 TW

World Gross Domestic Product (GDP)

World Energy Use 16 TW (US/Ger/China/India 3.5/0.6/3.5/0.9)

Absolute Spending Limit (GDP/Energy Use) U.S. $120/GJ Germany $190/GJChina $50/GJ India $50/GJ

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Fraction of U.S. GDP t

Max Total Spending on Energy ~ 10-15% of GDP< $5 -15/GJ: the lower the better.

spent on energy

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Raising the price of energy meansthe money must come from somewhere else.

Decreased Prosperity.

During times of relative economic stability and increasing world prosperity food and fuel are inexpensive

< 10-15% GDP

Food ~ $5 - 15/GJ and Fuel ~ $2 - 15/GJ

Corn $2.00 /bushel $7.90 /GJ

Rice  $2.00 /cwt $4.40 /GJ

Wheat $4 50 /bushel $16 46 /GJ

Oil $85.00 /barrel $13.94 /GJ

Coal $50.00 /ton $1.70 /GJNatural 

Gas $4.00 /MMBTU $3 70 /GJWheat  $4.50 /bushel $16.46 /GJ Gas $4.00 /MMBTU $3.70 /GJ

Gasoline $2.50 /Gallon $20.00 /GJ

Electricity $0.05 /kW‐hr $14.00 /GJ

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Bad Things Happen WhenFood and/or fuel > $15/GJ

2008Oil @ $150/bbl ~ $24/GJ

Wheat @ $16/b shel $56/GJWheat @ $16/bushel ~ $56/GJElectricity @ $0.15/kW-hr = $30/GJ

Cause or Effect ?

Here we go again?

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Where do most people (including scientists) think the money

will come from for new sources of sustainable energy?

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Sustainable = Environmental and Economical(non-toxic, renewable) (< $5 - 15/GJ)

n1

Annual Net Revenue($)Total Capital($)

(1 discount rate)

nn

year

Production Cost

nProduct Price1

n1

Total Capital($) 1 Product Price(1- )

System Output(GJ/y) (1 discount rate)

1 ~ 8 - 3 for DR~ 10 - 30%, n~10 years

(1 discount rate)

Total Capit

n

year

n

year

Production Cost

Product Price

al($) ~ 15($/GJ) (1- ) * 5 ~ 60($ / / )

System Output(GJ/y)y GJ y

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Energy Production Cost

Energy Product PriceTotal Capital($/Watt) 1.8 *(1 - )

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Science and Engineering have provided society with low costprocesses for economically sustainable energy production.

Can we do it both

$0.25 - 1/Watt

$1-3/WattSolar Wind Electricity

Can we do it both EnvironmentallyAnd EconomicallySustainably ?

$0.5-1/Watt

2050~ 30 TW

from where?

Solar Conversion Processes

200 W/m2 ~ 1 mMoles photons/m2s

Inputs Outputs

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Output Value - Input Costs - CapX - OpX > 0

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How to use solar radiation ?

Inputs Outputs

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Utilization of electrochemical potential from electronic excitations• (e-,h+) EMF Photovoltaics• (e-,h+) EMF, EChem Photosynthesis• (e-,h+) EMF, Thermal Wind, Hydro, Solar-Thermal

Earth as a conversion system• (e-,h+) EMF, Thermal Wind, Hydro• (e-,h+) EMF, EChem Photosynthesis

~ 1% Wind

~ 10% Hydro

120 000 TW Bi Oth

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120,000 TW Biomass, Other

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Cost-Effective Solar Energy Conversion: Wind and Hydro-Power

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Why Solar-to-Chemical Photosynthesis Works

200 W/m2200 W/m2

=0.1%

0.2 J/s-m2

Rice ~ $10-20/GJ Corn ~ $10-20/GJ

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0.0063 GJ/y-m2

~ $ 0.1/m2 year Revenue

Because, it costs farmers less than $0.1/m2-year to grow biomass,AND – only because they don’t need to produce very much of it.

~ 200 Watts/person

Rice $10-20/GJ Corn $10-20/GJ

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Why Solar-to-Electricity Does Not Work

200 W/m2200 W/m2

~ 10%

20 J/s-m2Electricity Value ~ $15/GJ

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0.63 GJ/y-m2

~ $ 10/y-m2 Revenue

A modern cell system installed @ $5/Wpeak

Capital Cost ~ $500/m2

Why $500/m2

It’s a wild world out there $$$

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price ($)

per m2

(not for land)

To be cost effective on capital alone, a solar converter must cost less than ~ $40/m2 for ~10% and less than ~ $400/m2@ =100%

(not for land)

paint (3 mils) 0.6plastic (6 mils PE) 1.1

plywood 6.5astro-turf 8.2sod lawn 8.6

vinyl flooring 10.81" concrete 13.5

tar roof 43 0

+ lots of landtar roof 43.0

roof tile 64.6Asphalt road 172.2

Si Solar Cell($5/W) 500.0Home Construction 1500.0

Only VERY Inexpensive Systems

land

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14

2009

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Google: Grid Parity?

28https://docs.google.com/present/view?id=dfhw7d9z_0gtk9bsgc&pli=1

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Wealthy nations (with low GDP growth) “tolerate” economically unsustainable renewables such as solar cells because

they are balanced by relatively low cost fossil/nuclear/wind

China ~ 3.5 TW

U.S. ~ 3.5 TW Germany~ 0.6 TW

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Chemical sciences and engineering must create options for massive quantities of sustainable sources

of energy that are affordable by all people

Cost reductions over the last decadel l d f i i

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are largely due to use of increasingnumbers of low wage workers not improved technology. The majority of the costs are paid from taxpayer subsidies.

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~1780

~1880 Adams&Day, Fritts

Se Solar Cells 1-2% efficiency)

More than 100 years of

Development No Significant Cost-EffectiveApplications

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C*(e-,h+)

e-

h+

A

D

e-

h+

A-

What about Solar-to-Chemical ? chemical potential

CC

D+

2e- + 2H+ +xCO2 CxH2Oz

H2O + 2h+ ½ O2 + 2H+

Reducing Potential

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Growth Driven By Unsustainable Economics

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Growth Driven By Unsustainable Economics

Biodiesel

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Can Man Beat Nature ? “Artificial” Photosynthesis

G. Ciamician, Science 1912

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Solar Energy, Volume 2, Issue 2, April 1958

Semiconductor Photoelectrodes

−E

RED

Photocathode

p type SC

h+

+ +

RED

OX

p-type SC

Photoanode

−

+

h−−

RED

OX

E

n-type SC

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Suspended PV “platelets”   1981Hydrogen

Platelets

N-type semiconductorp-type semiconductor

Ohmic contact

Platelet

100 + Years of Photoelectrocatalysis (PEC)

Science has provided efficient systemsbut not cost-effective energy production

TiO2 PEC

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PEC Air“Purifier”

2

Mosquito Trap

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Going Forward: Strategies and TacticsHow to do the right thing and get others to pay for it.

Options:1) Scare them into it.2) Keep making promises that are impossible

to keep.3) Create options that, if tough problems are

creatively solved, might ultimately prove economically sustainable.

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Is there a cost-effective solarPEC Process that can

make use of the material system?

Find and understand an efficient PEC material system

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Conceptual Engineering Process Models

Photoelectrodes = PV ($$) + electrolyzer($$)

Un-biasedPhotoelectrode(s)

Chemically biasedPhotoelectrode(s)

Electrically biasedPhotoelectrode(s)

Bottom Up vs Top Downdo not underestimate the engineering 

Design a conceptual cost-effective Solar Chemical Process

Can a material system befound that meets the

minimum requirements ?

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Artificial Photosynthesis

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~ 10%

~ 0.1 % ~ 0.1 %

Conceptual Engineering Process Models

Photoelectrodes = PV ($$) + electrolyzer($$)

Un-biasedPhotoelectrode(s)

Chemically biasedPhotoelectrode(s)

Electrically biasedPhotoelectrode(s)

A- DA + D A- D

Split Z-SchemeSlurry Photoreactor

Single TankSlurry Photoreactor

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Today, there is only one known system for solar fuels (hydrogen) which might make economic sense.

ASSUMES that a stable, =10% slurry material exists

Only slurry-based

James B, Baum G, Perez J, B.K. Technoeconomic Analysis of Photoelectrochemical (PEC) Hydrogen Production. Analysis 22201, (2009).

y ysystems might meet basic economic targets. $6/GJ

h

Can we do better than Nature?What structures should we make and calculate

D-

D

A

A-e-

e-

50

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Hybrid PEC “Nanoreactors”Low cost inorganic semiconductor based heterostructures

Our Strategy

Theory New/improved low cost semiconductors Understanding of excitation/separation/

de-relocalization of charge size shape composition

h+

e-

h A-

AD-

D

de-relocalization of charge size, shape, compositionInterface charge transfer. RecombinationElectrocatalysis

DSynthesis/Experiment New/improved low cost, high-quality semiconductors Heterostructures Diffusion barrier/encapsulation

A A-

Zn2+ Zno -0.76

-0.26V3+ V2+

Approach

h

Maximize Stored Solar Chemical Potential

D-

DA

A-

2I-1I2 0.54

D- D

(CnHm)OH (CnHm)O 0.6

2H+ H2 0.00

AgCl Cl-+Ago

0.34

0.22

Cu2+ Cuo

CO2 CH4 0.17

1) Identify cost effective optimal solar absorbing semiconductor Egap~ 1eV systems with IQE >90%.

h+

e-

H2O2H++1/2O2 1.23

2Br-1Br2 1.07

Fe2+Fe3+ 0.77

2Cl-1Cl2 1.36

g p

2) Select and match best practical redox systems that could provide stored energy G ~ 0.9*Egap

3) Maximize selective kinetics (minimize back reaction)

4) Determine means for stabilizing the material in the redox system

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HighThroughputMethodology

Al2O3 3000 Å

Al2O3 1500 Å

V 800 Å

V 1600 Å

SnO2 4800 Å

4000 Å

1000 Å

La2O3

4000 Å

1000 Å

Y2O3

4000 Å

1000 Å

MgO

4000 Å

1000 Å

SrCO3

Sample: 826962

Theory Guided

0 Å 530

Å

0 Å

260Å

0 Å

240 Å

0 Å

250ÅEu2O3 Tb4O7 Tm2O3 CeO2

Science 279, 837-839 (1998)

yLibrary Design:Diversity in CompositionDiversity in Synthesis

Rapid Synthesis and Processing:Electrochemical DepositionPVD, Ink Jet, Solgel, Parallel vs Rapid SerialSmall vs Large Element Size

High-Throughput Screening:Optical, Chemo-opticalPhotoelectrochemicalGC-MS

Start with a known reasonable host Try to make it better

Make efficient materialmore stable

Bak et. al., Int. J. Hydrogen Energy,vol 27 (2002) 991-1022

ZnnXmO

4045

WnXmOp

H2O/H2

O2/H2O

1.23 eV

Cu2O TiO2 Electrolyte

Eabs

(eV)

- 4

- 5

- 6

- 7

- 8

- 3

ENHE

(eV)

0

+1

+2

+3

- 1

- 2

2.0 eV

3.0 eV

0.30

Cu2O/XOn

0 20 40 60 80 1000

1

2

3

4

152025303540

Pho

tocu

rren

t(A

/cm

2 )

[Mo]

1V bias

zero bias

J. Combi. Chem. 4(6), 573-578, 2002

4 6 8 10 120.10

0.15

0.20

0.25

Ph

oto

curr

ent

(mA

/cm

2 )

pH

J. Comb. Chem., 7, 264-271, (2005)

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Doped: ZnO

The “Science” of Synthesis

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J. Comb. Chem., 7, 264-271, (2005)

WO3

4

15202530354045

ren

t(A

/cm

2 ) 1V bias

WnXmOp

MoO3

MoO3

W0 2Mo0 8O3

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0 20 40 60 80 1000

1

2

3

4

Pho

tocu

rr

[Mo]

zero bias

J. Combi. Chem. 4(6), 573-578, 2002500 550 600 650 700 750 800 850 900 950 1000 1050 1100

W0.2

Mo0.8

O3

W0.3

Mo0.7

O3

W0.5

Mo0.5

O3

W0.7

Mo0.3

O3

W0.8

Mo0.2

O3

WO3

Inte

nsi

ty (

a.u

.)

Raman Shift (cm-1)20 22 24 26 28 30

0.2 0.8 3

W0.5Mo0.5O3

W0.8Mo0.2O3

WO3

Inte

nsi

ty (

a.u

.)

2

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In spite of decades of research, there is no evidence thatwide gap oxides (TiO2, WO3, ZnO, …) can be modified to serveas efficient solar absorbing hosts. Fe ? Cu ?

Fe2O3

n-Type Indirect Bandgap 2 - 2.2 eV

40% solar spectrum absorbed

Globally scalable

Abundant, inexpensive

Non-toxic

Photo-stable against corrosion

Mott Insulator (Poor carrier transport )

Anisotropic conductivity

Low electrocatalytic activity

Theory Guided ExperimentationUndoped Fe3+

Fe2O3 Pt4+ doped Cr+3 doped Al+3 doped

LDA+U

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Flat Conduction band large effective mass, poor conductivity. 1) Majority Carrier Donor Concentration (traditional doping)2) Create Impurity bands which have smaller mass 3) Break C-T Mott Insulator, spin forbidden electron transport

LDA+UU=5.7 eV12 Fe +18 O

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Characterization of substituted Fe2O3

Bg=2.1 eV

J. Phys Chem C. 20(12),3803, (2008)

Chem. Mater., 20, 3803–3805, (2008)

Energy Env. Sci. 4,1020, (2011) 1%Ti

•Optical properties show little change with dopants • Higher valence dopants (n-dope) “helps”• Isovalant substitutions with large cation size differences (strain) “helps”

Delafossites (CuMX2)

CuCrOCu+

C 3+

Theoretical bandgapDirect: 3.0 eVIndirect: 2.1 eV

Experimental bandgap: 1.3 eV

CuCrO2Cr3+

In general, poor efficiency.

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Phosphides(start with an efficient material and make it more stable)

• Easy to make ( from libraries of oxides)• MxOy +H3PO4 ;  H2 at 900 C

• .

• Easy to break• Zn3P2 + 6H2O → 2PH3 + 3Zn(OH)2

Strategy -> keeph f

H+

Na6 [HxMyOz] + NH4HPO4MPOx + NH4OH +NaOH +H2O H2 at 900 C

FeP InP Zn3P2 NixPy WP MoP

them safe

Sulfides  (SnS)

Electrodeposited Film              powder

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Identification of efficient, stable, cost effective solar absorbing materials remains

the #1 challenge for solar energy PEC

Work to date with all oxides has been discouraging.

- Although their visible band absorption can be improved, not by nearlyAlthough their visible band absorption can be improved, not by nearly enough. The common wide gap oxide semiconductors (TiO2, ZnO, WO3) will not work as absorbers for solar fuel applications.

- Iron oxides are intrinsically poor candidates for solar PEC applications

TiO2

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and in spite of attempts to improve their properties they remain far too inefficient by 10-100x.

Sulfides and Phosphides Deserve More Attention

Don’t forget Si !

Silicon

Fe2O3 Last oxide hope CuxO

Theory Guided Identification of Active, Stable,  and Selective Electrocatalysts

h+

e-

h DD-2H+

H22“In situ membrane”

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Pt-Au Alloy Nanoparticles for ORR

Slope ~ ne

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Co/Au

Fe/Ni

Bimetallic OER Electrocataysts

CoAu

Pt/Au

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Electrochem.Com. 11 (2009) 1150–1153

Pt/Au

Choice of the electrocatalyst assumes you know the reaction you want.

2H+ H2A A-

What is the best form of the chemical potential product?

H2 fast, separable, easily reacted (H2+ CO2 CH4 )

1) High efficiency, cost-effective absorbers, Egap ~ 1eV.2) Identify stable redox chemistry that can be integrated into a major

chemical cycle.

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12

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Zero Bias NaOH Glycerol Erythritol Xylitol

(%

)

D- D

(CnHm)OH (CnHm)O2 electrodes 1 sun

Ti Doped Fe2O3

H2S2H++ S

2HBr 2H++ Br2

Avoid zero value products

350 400 450 500 550 600

0

2

4

6

8

IPC

E

Wavelength (nm)

H2O2H++1/2 O2

2HCl 2H++ Cl2

Get over water splitting!

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The formation of adsorbed OOH is limiting and only at high electrode potential is thisstep downhill in free energy. The process takes place on an oxidized surface. Oxygen evolution should start at E>1.8 V

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yg

Functional Nanoparticulate Heterostructures

Fe2O3@ZrO2

7010 nm

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Hybrid PEC “Nanoreactors”Low cost inorganic semiconductor based

heterostructures

Al2 O

3

Absorber

Ag (Ohmic Contact)

ħω

h+

e‐

Oxidizing reactant

Reduced product

Au or Pt (Schottky contact)

Reducing agent

Oxidized product

Mubeen J. Hussaini Francesca TomaMartin MoscovitsGalen Stucky

NiO

AAb

Electrodeposited Heterojunction in Porous Alumina

CdSe

Au

TiO2

Al2 O

3

bsorber

Mubeen J. Hussaini Francesca TomaMartin MoscovitsGalen Stucky

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Large Scale, Cost Effective Processes Are Typically Integrated

Large Scale, Cost Effective Processes Are Typically IntegratedProcess Alternative: CnHmOz H2 + CO2

H

(CnHm)OH + h+ (CnHm)O + H+

2e- + 2H+ H2

H2

Biomass orWastewater

CO2

X-ols

CatalystRegeneration

Reactor SeparationTreatmentSeparation

~ 1 kg/person/day organic waste (~ 1 TW )

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2e- + 2H+ H22Br-1Br2

Large Scale, Cost Effective Processes Are Typically IntegratedExample Process Alternative: 2HBr H2 + Br2

Biomass

Regeneration

O2 + HBr Br2 + H2O

Water Air

HBrBr2

Activation

CH4 + Br2 CH3-Br + HBr

Coupling

CH3-Br Gasoline + HBrBioMethane Gasoline

2

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Net Reaction: 8CH4 + (16/ C8H16 + 8H2 (Ideal)

Summary• Today there are no significant, cost‐effective, manmade solar 

conversion processes because no efficient, stable, scalable, and cost‐effective absorbing material system is known.  

• Recent advances in theory, complex surfaces, and synthesis of novel materials may have significant impact if directed wisely.  

• Water splitting may or may not ever be cost‐effective, but there are potentially many other solar‐to‐chemical conversions that might be more cost‐effective and ultimately more useful to mankind.  The system matters, many can never work.

• Fundamentally production of chemical fuels from solar energy at less than $15/GJ is possible, practically it is very very difficult.

Think outside the box or we will not succeed

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Th k YThank You

Collaborators: Alan Kleiman, Yong-Sheng Hu, PengZhang, Nirala Singh, Galen Stucky, Eric McFarland