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