ANA L. MOORE ARIZONA STATE UNIVERSITY
Artificial photosynthetic constructs for the production of fuel
!"#$"%&'(%&)*("#"%+,&-&&./($(0,#$/"0*0&
2012 SCIALOG CONFERENCE BIOSPHERE 2
October 9 – October 12
The anthropocene era
The term was coined in 2000 by the Nobel Prize winning atmospheric chemist Paul Crutzen, who regards the influence of human behavior on the Earth in recent centuries so significant as to constitute a new geological era. Nobel Prize 1995.
The term was coined in 2000 by the Nobel Prize (1995) winning atmospheric chemist Paul Crutzen, who regards the influence of human behavior on the Earth in recent centuries so significant as to constitute a new geological era.!
Nature 2009, 461, 472.
AA llaarrggee pprrooppoorrttiioonn ooff ssppeecciieess aarree ccuurrrreennttllyy tthhrreeaatteenneedd wwiitthh eexxttiinnccttiioonn ((1122%% ooff bbiirrddss,, 2233%% ooff mmaammmmaallss,, 3322%% ooff aammpphhiibbiiaannss;; 3311%% ooff ggyymmnnoossppeerrmmss;; 3333%% ooff ccoorraallss))..!!
The anthropocene is much more than green house gases/climate change problem; Earth is a complicated ecosystem and climate change is just one issue.
“Localized ecological systems are known to shift abruptly and irreversibly from one state to another when they are forced across critical thresholds. The global ecosystem as a whole can react in the same way and is approaching a planetary-scale critical transition as a result of human influence.”
Nature 2012, 486, 52.
Impacts of biodiversity on the emergence and transmission of infectious diseases
“Overall, despite many remaining questions, current evidence indicates that preserving intact ecosystems and their endemic biodiversity should generally reduce the prevalence of infectious diseases”.!
Nature 2010, 468, 647.
Felicia Keesing, Lisa K. Belden, Peter Daszak, Andrew Dobson, C. DrewHarvell, Robert D.Holt, PeterHudson, Anna Jolles, Kate E. Jones, Charles E. Mitchell, Samuel S. Myers, Tiffany Bogich & Richard S. Ostfeld
Biodiversity depends on photosynthesis
Photosynthesis powers the biosphere operating at
about 150 TW
Humans appropriate: ~25% of terrestrial photosynthesis.
Never has one species taken such large proportion of the available
resources.
1 TW = 1012 W!
We asked: Is there unused solar energy humans can take? No, photosynthesis and land use are all booked (overbooked) up. But, we need a huge amount of solar to change the trajectory of the anthropocene; to provide biomass to meet human needs.
What do do? 1)!We must not take any more of nature’s (the
biosphere’s) share of energy or land. 2) We must conserve and maximize efficiency
of land use, solar conversion, and energy use.
8
Plant photosynthesis is less than 1% efficient
Gust, Kramer, Moore, Moore & Vermaas, MRS Bulletin, 2008, 33, 383
Photosynthetic microorganisms do better, ~ 4%
Photosynthesis is inefficient - it can not keep up with the energy needs of 7 billion humans
Photosynthetic organisms respond to damaging high light levels by down-regulating the fraction of excitation energy that drives electron transfer.
Diatoms
Light saturation curve of photosynthesis
Photosynthesis saturates at light intensities well below maximum solar intensity 11
Three mechanisms that quench the excited state of chlorophylls
Carotenoids and power management in photosynthesis
Controlling ~66,000 TW to give 150 TW
Gust, Kramer, Moore, Moore & Vermaas, MRS Bulletin, 2008
Redesign photosynthesis to better match redox needs to solar spectrum
"a) extend single junction device to near IR ""b) design a two junction device
Solar spectrum 400 700 1100 nm
What are the rules for energy conversion efficiency?"
Shockley and Queisser J. Appl. Phys., 1961"."."."Hanna and Nozik, J. Appl. Phys., 2006" 13
A better match to the solar spectrum could result in a theoretical efficiency up to 40+%
14
Natural photosynthesis Z scheme
15
Z-scheme of oxygenic photosynthesis
PS I
Blankenship et al., Science 2011, 332, 805 16
A new presentation of the photosynthetic Z-scheme
Center for Bio-Inspired Solar Fuel Production a US DOE Energy Frontier Research Center
A tandem two junction artificial leaf as a paradigm for reengineering photosynthesis
The EFRC at ASU
Dye absorbs ONLY 400 to 730
Dye absorbs ONLY 730 to 1100
sun
Photosystem II (PSII) is the enzyme found in plants, algae and cyanobacteria
which uses solar energy to split water into molecular
oxygen and reducing equivalents
Active Branch Protective Branch
PSII a high potential reaction center
The London Structure (3.5 Å resolution) Science 2004, 303, 1831
TTiiOO22 ++ SS !!
SS!!
N N
N
N
NN
Ru2+
P
P
O
OH
OHO
OHOHO
OHOHO
PSII model
WWoorrkk aatt iinntteerrffaacceess!!
P680
2H2O + h! + "210mV !! 2H2 + O2
h!
S•+/S*
S•+/S0
emf
H+ Ions
Nafion
S = dye
cathode photoanode
In collaboration with Tom Mallouk W. J. Youngblood et al., J. Am. Chem. Soc. 2009, 131, 926
e -
Dye sensitized cell
-400 -300 -200 -100 0 100 200 300 400 -10 -5 0 5
10 15 20 25 30
I-V behavior of PEC cell
Applied Voltage (mV) vs. Ag/AgCl
Phot
ocur
rent
µA
Voc = 980 mV !"!O2
" 0.9%!
0 10 20 30 40 50 60 0 20 40 60 80
100 120 140 160 Photocurrent at V=0 vs. Ag/AgCl
Time (s)
Phot
ocur
rent
µA!
VB
CB
S•+/S*
S•+/S
e–
e–
Semiconductor
Dye
IrO2 2.2 ms 0.35 ms
Fast back electron transfer from TiO2 to oxidized dye and slow forward electron transfer from IrO2 to dye.
h!#
Suggestions for improvement
!! New dyes with higher oxidation potential. Porphyrins!
!! Use of different metal oxide and molecular catalysts.
!! Tune electron transfer rates. Use of electron relays.
Porphyrin based photoanode
Light source- Xe lamp with AM 1.5 filter, cell positioned to receive 100 mW cm-2 light intensity, + 200 mV vs. SCE .
Stable photocurrent
!! Use of different catalysts
Heterogeneous catalysts for water oxidation
A. Harriman, et al., J. Chem. Soc., Faraday Trans I, 1988, 84, 2795.
Observed rates of O2 evolution for oxide catalysts under photochemical conditions
A new method for preparing a nanoparticulate cobalt oxide catalyst for
water oxidation
!"#
Wee T-L. et al. J. Am. Chem. Soc., 2011, 133, 16742–16745
Preparation of Co oxide NP, a photo-reduction approach
S
O
N
O
h! (UV")
MeCN, ArS
O
N+
CoCl2
Co NPairCo2O3 NP
Scaiano’s Lab
Molecular water-oxidation catalysts
Meyer et al., J. Am. Chem. Soc., 2008, 130, 16462.
Meyer et al., J. Am. Chem. Soc., 1985, 107, 3855.
Brudvig, Crabtree et al., J. Am. Chem. Soc., 2009, 131, 8730. Brudvig, Crabtree et al., Science, 1999, 283, 1524.
!! Use of electron relays to prevent back electron transfer from the semiconductor to the oxidized dye.
Notice a high potential mediator/relay between P680 and OEC
PSII, nature’s high potential reaction center
Y. Umena et al. Nature 2011, 473, 55.
P680
VB
CB
S•+/S*
S•+/S
e–
e–
Semiconductor
Dye
IrO2 2.2 ms 0.35 ms
Adding the mediator (M) to speed reduction of S•+ and lower the yield of recombination
h!#
M(ox)/M(red) e–
.
Redox potentials: (O2/H2O) and estimated for OEC and P680•+
Eo vs. NHE (V)"
0.8
1.0
~1.3
M(ox)/M(red
natural system
BBIIPP!!2-(3’,5’-di-tert-butyl-2’-hydroxyphenyl)benzimidazole
Tyrz–hystidine model
Gary Moore
Effects of the protonation state on the redox potential of BIP
G. F. Moore et al. J. Phys. Chem. B 2010, 114, 14450.
.
PSII relay/mediator poised between P680•+ and OEC (O2/H2O) by control of H+ activity
Eo vs. NHE (V)"
<0.8
~0.9
~1
~1.3
>1.3
Use of an electron relay (BIP) between the P680 mimic and the water oxidizing catalyst
IInn ccoollllaabboorraattiioonn wwiitthh TToomm MMaalllloouukk !!
Zhao et al. Proc. Natl. Acad. Sci. USA 2012, 109, 15612.
Use of an electron relay (BIP) between the P680 mimic and the water oxidizing catalyst
IInn ccoollllaabboorraattiioonn wwiitthh TToomm MMaalllloouukk !!Photocurrent of the Ru-dye sensitized TiO2 photoelectrodes with uncapped IrOx!nH2O and mediator-IrOx particles. Zhao et al. Proc. Natl. Acad. Sci. USA
2012, 109, 15612.
40
Shorter lifetime of Ru•+ in the presence of the mediator
Normalized transient bleaching recovery curves monitored at 464 nm TiO2 electrodes with adsorbed Ru dye (black), Ru dye + IrOx!nH2O (purple) and Ru dye + mediator-IrOx!nH2O (blue)
Use of an electron relay between the P680 mimic (porphyrin) and the water oxidizing catalyst
OH Resonance = 14.5 ppm in CDCl3 Stronger Hydrogen Bond
OH Resonance = 13.2 ppm in CDCl3 Weaker Hydrogen Bond
Ideal situation for H Bond: pKa H-DONOR = pKa H-ACCEPTOR
pKa ~ 6
pKa ~ 10
•! In 1 inductive effect of PF10 reduces the basicity of the Imidazole (decreases the pKa) while the phenol does not feel the effect (same pKa).
•! In 2 inductive effect of PF10 increases the acidity of the phenol (decrease the pKa). James M. Mayer PNAS, 2008, 105, 8185.
1
2
Challenge to attach the bio-inspired dyads to the IrOx-NPs
Our systems are:
"!Hydrophobic "! Tend to aggregate in water "!Sensitive to basic pH at high temperature
New versatile method to functionalize the IrOx-NPs.
Artificial Photosystem II
• –
• +
h!!##
Megiatto et al. Proc. Natl. Acad. Sci. USA 2012, 109, 15578.
Photophysical studies of BIP in photoinduced charge separation
LUMO of the tetracyano porphyrin as a model of the CB of the semiconductor
light • – •+
Megiatto et al. Proc. Natl. Acad. Sci. USA 2012, 109, 15578.
Relevant states and decay pathways 41
4 µµs, long lived charge separation!
$ = 77% #
$ = 52% #
Artificial Photosystem II
4 µµs, long lived charge separation ~ 50% Q.Y.! PCET?
• –
• +
h!!##
The long lifetime of the highly oxidizing relay provides a good match for the slow kinetics of the OEC or metal oxide catalysts.
Megiatto et al. Proc. Natl. Acad. Sci. USA 2012, 109, 15578.
Center for Bio-Inspired Solar Fuel Production a US DOE Energy Frontier Research Center
A tandem two junction artificial leaf as a paradigm for reengineering photosynthesis
The EFRC at ASU
Dye absorbs ONLY 400 to 730
Dye absorbs ONLY 730 to 1100
sun
Absorption and redox potential considerations
49 ~ 1.5 V vs. NHE ~ 0.8 V vs. NHE
PS I
Axially substituted SiNc
EExxtteennddeedd aabbssoorrppttiioonn iinnttoo!!tthhee nneeaarr IIRR ((uunnttiill ~ 990000))!!
Pablo Turati Monterrey Tec, México
moving the CB of TiO2 more negative
%E peak
1st rdxn -0.79 vs SCEa 62 mV
2nd rdxn -1.13 vs SCEa 68 mV
1st oxdn 0.36 vs SCEa 61 mV
2nd oxdn 0.75 vs SCEa 62 mV
a)! Reversible process.
-1.5 -1.0 -0.5 0.0 0.5 1.0
-1.0x10-6
-5.0x10-7
0.0
5.0x10-7
1.0x10-6
i am
p
E volt vs SCE
Pt electrode, 100 mV/s.
Exp: DCM, 0.1 M TBAPF6. Pt working electrode, Pt counter electrode, Ag wire reference. Ferrocene was added to the solution at the end of the experiment and the potential was corrected by using the ferrocene couple as reference. (450 mV vs. SCE).
Pc on TiO2 Black (dashed)- Pc in DCM
Voc = 0.46 V Jsc = 3.14 mAcm-2
FF = 0.63 ! = 0.9%
Peripherally substituted phthalocyanines
Dalvin Méndez
E1/2 vs. NHE (V)
– 0.63 TiO2 ECB(FTO, pH8)
– 0.07 SnO2 ECB(ITO, pH7)
– 0.47 2H+ + e- H2 (pH8)
– 0.83
0.60 Nc•+ + e- Nc
Nc•+ + e- Nc*
– 0.63 TiO2 ECB(FTO, pH8)
– 0.07 SnO2 ECB(ITO, pH7)
– 0.47 2H+ + e- H2 (pH8)
Energetics for low potential reaction centers
radical cation (Nc.+) is not oxidizing enough to oxidize water
A two junction artificial leaf
PSII
400 900 650
Wavelength (nm)
PSI
aH2ase H+
" H2
" H2O
# O2 aOEC
N
NN
NN
N
N NSi
O
O
O
O
O
O
O
O
O
OR
O
MPS4
CB
CB
55
Catalytic Turnover of [FeFe]-Hydrogenase Based on Single-Molecule Imaging
C. Madden, M. D. Vaughn, I. Díez-Perez, K. A. Brown, P. W. King, D. Gust, A. L. Moore, and T. A. Moore
supported by the US Department of Energy, Office of Basic Energy Sciences as part of an Energy Frontier Research Center
Tijana Rajh Oleg Poluektov
Tom Mallouk’s lab Rudi Berera Miroslav K. Kloz John Kennis Rienk van Grondelle
Dept. of Physics Politecnico di Milano
Margherita Maiuri Dario Polli
Giulio Cerullo
