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Transcript of Solar Production of Fuels and Chemicals; is there a … Solar Production of Fuels and Chemicals; is...
1
Solar Production of Fuels and Chemicals; is there a cost-effective path forward?
1
• 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
2
p g y
• Beyond Water Splitting
2
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.
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.
8
5
$ 63,000,000,000,000~ $120/GJ
512,000,000,000 GigaJoules
9
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
6
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
11
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
7
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?
14
8
Where do most people (including scientists) think the money
will come from for new sources of sustainable energy?
15
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
16
Energy Production Cost
Energy Product PriceTotal Capital($/Watt) 1.8 *(1 - )
9
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
18
Output Value - Input Costs - CapX - OpX > 0
10
How to use solar radiation ?
Inputs Outputs
19
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
20
120,000 TW Biomass, Other
11
Cost-Effective Solar Energy Conversion: Wind and Hydro-Power
21
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
22
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
12
Why Solar-to-Electricity Does Not Work
200 W/m2200 W/m2
~ 10%
20 J/s-m2Electricity Value ~ $15/GJ
23
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 $$$
13
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
26
16
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
31
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
32
are largely due to use of increasingnumbers of low wage workers not improved technology. The majority of the costs are paid from taxpayer subsidies.
17
33
~1780
~1880 Adams&Day, Fritts
Se Solar Cells 1-2% efficiency)
More than 100 years of
Development No Significant Cost-EffectiveApplications
18
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
35
Growth Driven By Unsustainable Economics
36
19
Growth Driven By Unsustainable Economics
Biodiesel
37
Can Man Beat Nature ? “Artificial” Photosynthesis
G. Ciamician, Science 1912
20
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
21
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
42
PEC Air“Purifier”
2
Mosquito Trap
22
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.
43
Is there a cost-effective solarPEC Process that can
make use of the material system?
Find and understand an efficient PEC material system
23
Conceptual Engineering Process Models
Photoelectrodes = PV ($$) + electrolyzer($$)
Un-biasedPhotoelectrode(s)
Chemically biasedPhotoelectrode(s)
Electrically biasedPhotoelectrode(s)
Bottom Up vs Top Downdo not underestimate the engineering
Design a conceptual cost-effective Solar Chemical Process
Can a material system befound that meets the
minimum requirements ?
24
Artificial Photosynthesis
47
~ 10%
~ 0.1 % ~ 0.1 %
Conceptual Engineering Process Models
Photoelectrodes = PV ($$) + electrolyzer($$)
Un-biasedPhotoelectrode(s)
Chemically biasedPhotoelectrode(s)
Electrically biasedPhotoelectrode(s)
A- DA + D A- D
Split Z-SchemeSlurry Photoreactor
Single TankSlurry Photoreactor
25
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
26
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
27
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)
28
Doped: ZnO
The “Science” of Synthesis
55
J. Comb. Chem., 7, 264-271, (2005)
WO3
4
15202530354045
ren
t(A
/cm
2 ) 1V bias
WnXmOp
MoO3
MoO3
W0 2Mo0 8O3
56
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
29
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
58
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
30
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.
31
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
32
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
63
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”
34
Co/Au
Fe/Ni
Bimetallic OER Electrocataysts
CoAu
Pt/Au
67
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.
10
12
14
16
18
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!
35
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
69
yg
Functional Nanoparticulate Heterostructures
Fe2O3@ZrO2
7010 nm
36
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
37
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 )
38
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
39
77
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