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Artificial Photosynthesis:
Imitating Nature to Produce
Clean Fuels
Perspectives of Modern Biology & Biotechnology Series
Faculty of Biology, University of Warsaw
12 November 2015
Joanna Kargul
SolarFuels Laboratory
Centre of New Technologies UW
solar.biol.uw.edu.pl
World Population Map
2015: 7.4 billion
2050: 10.5 billion
From M. Newman© 2006 M. E. J. Newman (University of Michigan).
http://www-personal.umich.edu/~mejn/cartograms/
Energy Consumption World Map
From M. Newman© 2006 M. E. J. Newman (University of Michigan).
http://www-personal.umich.edu/~mejn/cartograms/
World Energy Gap Problem
EIA Intl Energy Outlook 2013
http://www.eia.doe.gov/oiaf/ieo/index.html
%
83% fossil fuels37% oil
2100: 40-50 TW 2050: 25-30 TW2012: 16-17 TW
0.00
5.00
10.00
15.00
20.00
25.00
1970 1990 2010 2030
TW
Global Energy Consumption
Total
USA
EU/Russia
Global Demand:
~ 30 TW 2050
~ 50 TW 2100
developeddeveloping
10 TW = 10 000 1 GW Nuclear Power Stations (NPS) or 1 NPS daily for 27 yrs
EIA, Annual Energy Outlook 2013
http://www.eia.gov/forecasts/aeo/er/pdf/appa.pdf
http://www.eia.gov/forecasts/aeo/er/pdf/tbla17.pdf
Reproduced from: Stephens E. et al. Future prospects of microalgal biofuel production
Systems. Trends Plant Sci. 2010;15(10):554–564
Janna Olmos and Kargul. Oxygenic photosynthesis: translation to
solar fuel technologies. Act Soc Bot Pol. 2014;83(4):423–440
GLOBAL WARMING
IN THE LAST
MILLENIUM
Very rapidly we’ve entered uncharted
climatic territory -– the
anthropocene. Over the 20th century,
human population quadrupled and
energy consumption increased
sixteenfold. Near the end of the last
century, a critical threshold was
crossed, and warming from the fossil
fuel greenhouse became a dominant
factor in climate change.
Hemispheric mean surface
temperature is higher today than at
any time in the last millennium -- the
so-called Mann et al. “hockey stick.”
Temperatures are likely to go “off the
scale” in the 21st century.
Renewable Carbon-free Energy Sources
0.4
1.11.3
10
120,000
.17
Hydro Tidal Wind Geotherm. Solar Current use
0.1
1
10
100
1000
10000
100000
1000000
TW (Log scale)
?
adapt. z: Basic Research Needs for Solar Energy Utilization, DOE 2005
30
Nuclear
Renewables are still a small (2%) share of total energy supply,of which solar electricity below 0.01%…
Increase of Reneweable Energy Usein Europe (2004-2010)
Global Oil Supply:
3 billion (=Tera) barrels
1.7 x 1022 J =
1.5 day of sunlight
Annual Energy Production:
4.6 x 1020 J =
1 hr sunlight
Our Planet is Energy Rich!
The SunNuclear Reactor
149 600 000 km
From Earth
1.2 x 105 TW reaches the Earth
36,000 TW reaches continents
Energy used: 16 TW
Need to collect
the highest density of
energy, especially in
the form of chemical
bonds in liquid fuels
(such as in gasoline
and kerosene)
Nature found the way
to convert 120,000 TW
solar energy into
chemical energy using
water and CO2
Macroscopic Reaction Vessel
2H2O O2 + 4H+ + 4e-sunlight
organic carboncompounds,fossil fuels
+CO2
PHOTOSYNTHESIS
© NASA
Global Photosynthesis:
The Engine of Life
Animacja: SeaWiFS Project and the NASA GSFC Scientific Visualization Studio.
http://visibleearth.nasa.gov/view_rec.php?id=1664
1000 millions years to produce
fossil fuels and used in ~ 1000 years
0r
One year of fossil fuel consumption =
one million years of photosynthesis
5 Billion Year Clock
H2O splitting
~3 bln yrs ago
Big Bang of
Evolution
Oxygenic atmosphere
&
Ozone layer
2H2O O2+ “2H2”
Solar Energy Light reaction
“2H2” + CO2 (CH2O)Organic
molecules
Dark reaction
The Two Basic Reactions
of Photosynthesis
6H20 + 6CO2 C6H12O6 + 6O2
For every molecule of O2 evolved,
one molecule of CO2 is reduced.
Stoichiometry of Oxygenic Photosynthesis
Atmospheric CO2 0.039% by volume (387 ppm)
O2 21% by volume
a factor of ~500x difference
2H2O 4H+ + 4e
CO2
CO2
O2
O2
Solar Energy(120,000 TW)
photosynthesis
respirationcombustion
light reactions dark reactions
Biology adopted the perfect solution to
the energy problem
EnergyDecreased entropy
(metabolic energy)
& heat
“Almost cyclic
and sustainable”
CH2O
Organic
moleculesbiomass
food
fossil fuels
200 TW
0.2% efficiency
2H2O 4H+ + 4e CH2O
Organic
molecules
CO2
CO2
O2
O2
Solar Energy(120,000 TW)
photosynthesis
respiration biomas
food
fossil fuels
combustion
light reactions dark reactions
Biology adopted the perfect solution to
the energy problem…But
Energy(16 TW 30 TW) 200 TW
0.2% efficiency
“Not Cyclic”..seriously
out of balance
Solar Land Area Requirements
at 10% efficiency
6 at 3.3 TW EachFrom M. Newman
© 2006 M. E. J. Newman (University of Michigan).
http://www-personal.umich.edu/~mejn/cartograms/
2H2O O2+ “2H2”
Solar Energy
Water splitting enzyme
Photosystem II (PSII)
“2H2” + CO2 (CH2O)organic
molecules
Carbon (CO2) fixing enzyme
RuBisCo
Thylakoid membranes
(Light reactions)
Stroma
(Dark reactions)
PSIPSII
Nature’s Water Splitting and ProtonReducing Catalysts: PSII and PSI
stroma
lumen
nH+
nH+
ADP + Pi ATPhν
(H2O)
nH+ nH+
ATP synthase
(Mn4)
H+
O2
P680
Chl
Pheo
Chl
Pheo
QB
YzYD
Fe PQ Qi
Qo
cytbH
cytbL
cytf
PQ
PQH2
Fe-S
Photosystem II Cytochrome b6f
PQ
PQH2
nH+
QA
e-
e-
Photosystem I
Fd
P700Chl
A0
Chl
A0
Fx
FBFA
A1 A1
branch A branch B
PC/
cyt c6
hν
FNR FdNDH
NADP+ + H+
FNR
Fd
NADPH
e-
Calvin-
Benson
cycle
P
G
R
L
1
PGR5
CO2
e- e-
Components of Photosynthetic Light Reactions
Janna Olmos and Kargul (2015) Int. J. Biochem. Cell Biol., 66, 37-44
+0.815 eV O2/H2O
-0.320 eV NADP+/NADPH
P680+ strong oxidant: Em ~ +1.25 eV
P700* strong reducer: Em ~ -1.30 eV
Ox.
Red.
PSII and PSI as Perfect Einstein
Photoelectrical Devices: Blueprint for APS
Quantum efficiency: PSI = 1, PSII = 0.90
(like no man-made system)
Red.
+1.25
-0.58
-0.03
+0.43
-1.3
-0.58
2H2O O2+ “2H2”
Solar Energy Light reaction
The Water Splitting Reaction:
Energetically demanding process
Occurs with minimal overpotential
Photosystem II (PSII)
Water splittingrapid turnover of D1
“a repair process”
0
-1
+1
P680+
P680*Pheo-
PQA
PQB
Redox
scale
eV
P680+ is highly oxidising
Em ~ 1.25 eV at pH 7
Tyrz (YZ)
H2O
Red.
Oxid.
Electron transfer in Photosystem II
H+
PSII: Biological Smart Matrix for Solar Water Splitting
Lumenal view
Ferreira et al. 2004 (PDB 1S5L)
Active Branch Protective Branch
Ferreira et al. 2004 (PDB 1S5L)
PSII: Charge Separation Smart Matrix
Umena et al (2011) Nature, 473, 55–60 (PDB 3ARC)
Water Oxidising Catalyst of PSII
at 1.9 Å
Water splitting reaction
is a four photon process
2H2O + 2PQ O2 + 2PQH2
Light (4hv)
PSII
Oxygen emission induced by flashes
Joliot & Kok ~1969
ee--
ee-- ee--
ee--
O2
S4
YZ
P680+1st
Photon
2nd
Photon
3rd
Photon
4th
Photon
S4
HH++
S3
70 µs
190 µs
1.1
ms
30 µs
200 µs
S0 S2
S1
'
ee--
ee-- ee--
ee--
O2
S4
YZ
P680+1st
Photon
2nd
Photon
3rd
Photon
4th
Photon
S4
HH++
S3
70 µs
190 µs
1.1
ms
30 µs
200 µs
S0 S2
S1
'
H+
+
4
3Mn 21
Ca
Tyr 161
His 190
CP43Arg 357
Asp 61
3rd
1100 µs
2nd
1st
< 1 µs
200 µs
Thylakoid Lumen
e-
e-
P680*
Haumann et al.,
Science, 2005
Water-oxidation cycle of the Mn4Ca-complex of Photosystem II
S
S
S
S
S
1
2
34
0
O2
Mn
Mn
Mn
Mn3+ 3+
4+ 4+
Mn
Mn
Mn
Mn3+ 4+
4+ 4+
Mn
Mn
Mn
Mn4+ 4+
4+ 4+
Mn
Mn
Mn
Mn3+ 3+
4+ 3+
?
e-
e-
e-
e-
Tyr+
Tyr+
Tyr+
Tyr+
P680+ P680
+
P680+
P680+
hn
hn
hn
hn
dark state
1
2
3
4
100 µs
250 µs
1.5 ms
30 µs
see, e.g., Dau and Haumann,Coord. Chem. Rev. 2008,
and refs. therein.
(?)
QAQB
YZ P680
Phe
2H2O
O2
QH2
Mn4
D1/D2
Em
(V)
1.0
0.5
0.0
-0.5
-1.0
-1.5
H2O
Yz
OEC
P680
Ph
QA
P680*
QB
QP
cytb6f Fe-SR
PC (cytc)
P700
P700* (Em -1.26V)A0 [Chl]
A1 [Q]
Fe-SX
Fe-SA
Fe-SB
Fd
FNR
NADP
PSII PSI
P870
(P960)
P870*
BChl
BPh
QA
QB
Purple
Bacteria
P840
P840*
A0 [Chl]
A1 [Q]
Fe-SX
Fe-SA
Fe-SB
Fd
NAD
Green Sulphur
Bacteria
Em
(V)
1.0
0.5
0.0
-0.5
-1.0
-1.5
Kargul, J. and Barber, J. (2011) In: “Molecular Solar Fuels” (eds. W. Hillier, T. Wydrzynski), RSC Publishing, p 107-42
• charge separation quantum yield ~1: perfect Einstein photoelectrical device
• exceptionally long-lived charge-separated state P700+FB- (∼60 ms)
• exceptionally low redox potential of the distal FB cluster (Em ~ -580 mV)
• sufficient driving force for H+ reduction into H2 (H+ reduction potential under
physiological conditions of ~ -250 mV vs. SHE)
PSI: Perfect Einstein Photoelectric Device
Electron Transfer Chain in PSI
Kargul J, Janna Olmos JD, Krupnik T (2012) J Plant
Physiol., 169, 1639-1653
Jordan et al. (2001) Nature, 411, 909-17+
-
+
-
Artificial Photosynthesis for Solar Fuel Production
H2Carbon-based
Fuels(CO, CH4, HCHO,
CH3OH etc.)
H2Carbon-based
Fuels(CO, CH4, HCHO,
CH3OH etc.)
Primary photosynthetic
events: unparalleled efficiency
Janna Olmos and Kargul. Oxygenic photosynthesis: translation to solar fuel
technologies. Act Soc Bot Pol. 2014;83(4):423–440
Efficiency of solar-to-biomass: 0.2%
Targetted solar-to-fuel efficiency: 10%
2H2O 4H+ + 4eOrganic
molecules
CO2
CO2
O2
O2
Solar Energy
photosynthesis
respiration
biomass
food
fossil fuelscombustion
light reactions dark reactions
H2
Hydrogenase
The Artificial LeafH2/O2/H2O cycle driven
by solar energy
The Perfect Solution
“Cyclic”
Energy
Total global (16TW)
2H2O 2H2
O2
O2
Solar Energy (120,000TW)
Energy
Total global (16TW)
Liquid fuel
One hour of solar =
annual global energy consumption
H2/O2/H2O cycle driven
by solar energy
The Perfect Solution
“Cyclic”
+CO2
The Artificial Leaf
2H2O 2H2
O2
O2
Solar Energy (100,000TW)
Energy
Total global (14TW)
“If a leaf can do it
we can do it”
“Its only chemistry”
One hour of solar =
annual global energy consumption
2H2O 2H2
The
Artificial
Leaf
Liquid Fuels
Our Dream
Solar Energy (120,000 TW)
Global Energy Use
(17 TW)
O2
O2
+CO2
H2-O2-H2O Cycle Powered by Solar
Tandem(bio)Hybrid Device
Interdisciplinary Approach → Smart Design of Catalysis into Smart Matrix
Smart
Design
Solar-to-Fuel Nanodevice:
Artificial Leaf
QM/MM
Modelling
Material
Science
Biophysics,
Chemistry
Biology
Nanoscience
Photosynthesis PV & current into chemical energy
O H22
PP M
e
PP
e
M
CO
Sugar
H O
O
2
2
2
Solar-to-Chemical Energy Conversion
Semiconductor/liquid junctions
NEED: ≥10% efficiency in the laboratoryNEED: cheap materials stable in water, proper redox catalysts on each electrode, nanoscale engineering of efficient electron transfer, macroscaling
Anode Cathode
H2O
Artificial or semi-artificial
H
MnIV
MnIVMnIVMnV
O
O
CaO
OO
Cl
O
anode
catalyst
Dan Nocera
MIT
Kanan et al. (2008) Science, 321, 1072–1075; Kanan et al. (2010) JACS, 132, 13692–13701
Cobalt (IV)-oxo-phosphate: self-renewable water-
splitting catalyst operating at neutral pH
Overpotential of
400 mV (in PSII 300 mV)
hv
e-
e-
C60-Por-Bi-PhOH
Buckminsterfuleren
Tom Moore
ASU
Acceptor
Donor
From Natural
A Q Q B
P 680
O
Mn
Mn
Tyr
Acceptor
N
EtO 2 C
NH
O
NN ON N
N NO OO
Me Me
Me
MnMn
Ru
NN
N
NN
to
Photosynthesis
Artificial
Hammerstrom & Styring
U. of Uppsala
Calvin-Benson CycleRuBisCO
J. Phys. Chem. A
106(2002) 4773-
4778
J. Phys. Chem. A 103 (1999) 7742 - 7748
Leaf-architectured 3D APS of Perovskite Titanates
for CO2 Photoreduction into Hydrocarbon Fuels
Zhou, Ye et al. (2013) Sci. Rep., 3, 1667
• Nanostructured ATiO3
(A= Sr, Ca, Pb) perovskite
titanates as catalysts for
CO2 photoreduction to
CO and CH4
• UV-VIS photoreduction of
CO2 using H2O as e- donor
• Doping of STO and CTO
with Au co-catalyst (e- reservoir)
for best solar-to-hydrocarbon
quantum yield:
improvement of PCET
• Leaf 3D architecture inspired
macropore framework of
mesoporous crystalline ATO
for improved gas diffusion
and light harvesting
• SrTiO3 photocatalyst for
water splitting w/o external
bias potentialcheery leaf biotemplate
Biohybrid Devices
PSI and PSII-based Solar-to-Fuel
Nanodevices
Biohybrid Artificial Leaf
• Optimised for energy and charge
transfer (IQE ~ 100%)
• Self-assembling
• Cheap to obtain
• Non-toxic
Wiring PSII and PSI together → proof of the principle, rather than the
solution (stability and renewability problems).
Mimic biological smart design for water oxidation: self-renewability, high TOF
and TON, energetically balanced, operating at minimal overpotential, good
management of PCET, combining efficient charge separation and catalysis with
minimal losses due to back reactions
Wiring PSII and PSII (1)
Wiring PSII and PSII (2)
• 1st experimental setups to serially couple PSII and
PSI (see Kothe et al, Angew. Chem. Int. Ed. 2013,
52, 14233 –14236; Yehezkeli et al. Small 2013, 9,
2970–2978)
• Os-functionalised redox hydrogels
• Water as the sole e-/H+ source
• Closed PEC system w/o sacrificial electron donors or
acceptors; BUT: quantum efficiency 3.6*10-7%
pH 6.5 pH 5.5
Proof of the principle
Kothe et al., 2013
Biohybrid PSI-based artificial leaf
PSI in a Photocathode
Janna Olmos and Kargul (2015) Int. J. Biochem. Cell Biol., 66, 37-44
PSI as a Photocathode for H2
Utschig et al., 2011
246 µmol H2 mg Chl-1 h-1
Qian et al., 2008
0.50 µmol H2 mg Chl-1 h-1
Evans et al., 2004
0.09 µmol H2 mg Chl-1 h-1
Lubner et al., 2011
2200 µmol H2 mg Chl-1 h-1
Grimme et al., 2009
100.6 µmol H2 mg Chl-1 h-1
Krassen et al., 2009
3000 µmol H2 mg Chl-1 h-1
Kargul J, Janna Olmos JD, Krupnik T (2012) J Plant Physiol., 169, 1639-1653
Modular Design of a Bio-Inspired Tandem Cell for Direct Solar-to-Hydrogen Conversion:
EuroSolarFuels Consortium design of the chlorosome cylindrical
nanorods into a supramolecular
dye photosensitizer of RCs
design of the synthetic Zn-chlorin
cylindrical rods as an additional
photosensitiser of the artificial RCs
development of novel stable synthetic
catalysts for water oxidation
(Ru4-oxo cluster and mononuclear
Ir-derived catalysts) and hydrogen
production (Fe2S2 catalysts)
application of highly robust
and stable LHCI-PSI complex of C. merolae
as a biological module of the photocathode and photoanode for hydrogen
production (Solar Fuels Lab in Warsaw)
8 Interdisciplinary Laboratories from 6 European Countries:
de Groot (Holland), Holzwarth (Germany), Barber (UK), Kargul (Poland), Gryko (Poland),
Reek (Holland), Barbieri (Italy), Ocakoglu (Turkey)
artificial
biohybrid
Cyanidioschyzon merolaeas a model organism
thermophilic and acidophilic
unicellular red alga isolated from
acid hot springs rich in sulphate
(lab: pH 2.5, 42C)
one of the most primitive algae
(one nucleus, one mitochondrion
and one plastid); diverged near
the root of red algal lineage
all the three genomes (nucleus,
mitochondrion and plastid) fully
sequenced. Few introns and low
redundancy (mol. genetics and
mutagenesis feasible)
robust and highly active
PSII and PSI
Robustness and high activity of C. merolae PSII
Krupnik et al (2013) J Biol Chem, 288, 23529-23542.
Robust PSI-LHCI from C. merolae operates in a broad range of extreme conditions
Janna Olmos,
van Bezouwen
Boekema, Kargul,
in preparation
anode cathode
C. merolae PSI:
•~640 kDa monomer
•4 Lhcr subunits asymmetrically
attached to the core domain
0.0
0.2
0.4
0.6
0.8
1.0
1.2
400 500 600 700
678
RT Absorption Spectrum
of C. merolae PSI
Busch et al. (2010) Plant J, 62, 886-897
Need a highly stable
active PSI:
Use extremophiles
C. merolae LHCI-PSI
PRC
What we do in
SolarFuels group at UW?
LHCI-PSI
2H+ H2
hν
cyt c-553red cyt c-553ox
Ascox Ascred
In vitro reconstitution
of H2 production with
PSI and H2ase
Fd
MBH
His6
PtPt
Pt
cyt c-553
(petJ)
LHCI-PSI
2H+ H2 hν
narrow band gap
mesoporous semiconductor
membrane (Si, TiO2, hematite, other?)
e-
H+
H+
Goal 1
Goal 2
Platinisation of PSI
Immobilisation of Pt-PSI
Ni-NTAHis6
hν
2e-
2H+
H2
cyt c6 Asce-
Utschig et al. (2011) J. Am. Chem. Soc, 133, 16334-16337
Alternative to Pt: Self-assembled
PSI-cobaloxime complex
• self assembles in the dark
• O2-toterant
• catalytic for H+ reduction with low
overpotential
• comparable H2 production
rate as for Pt (250 µmol H2/mgChl/h)
• cheap and abundant
e-
e-
Molecular Wiring of PSI for
Efficient H2 Production:
Minimisation of e- DiffusionJohn Golbeck and colleagues
• Selecting the [4Fe-4S] cluster for short-
circuting with moleculer wire
• Selecting the molecular wire molecule
• Selecting the proton reduction centre
(H2ase or synthetic PRC)
• Proper interfacing of the modules
Wiring PSI [4Fe-4S] FB Cluster to
Proton Reduction Centre
Of/Derived from Hydrogenase
PSIcyt
c-553
4H+
2H2
hν
ascorbatered
ascorbateox
wireS-S PRC
immobilisation molecular wiring
S-SFB
Selecting the [4Fe-4S] cluster for short-
circuiting with the molecular wire
79
Possible Aliphatic and Aromatic
Molecular Wires
S
S
HH
HH
H
H
HHH
H H
H
H
H
HH
H
H
1,8-oktanedithiol*
S
H
HH
H H
HH H
H
H
H
H H
S H
1,6-hexsanedithiol*
S
SH
H
H
HH
H
H
H SS
H
H
H
H H
H
H
H
H
H
1,6 thiol-1,3,5-hexatriene biphenyl-4,4'-dithiol
80
*Golbeck et al.
oligothiophenes benzene-1,4-dithiol
Selecting the Proton Reduction
Centre: Hydrogenase Catalytic
Site[Fe-Fe] hydrogenase [Ni-Fe] hydrogenase
(Green Algae) (Cyanobacteria)
[Fe-Fe] hydrogenase 10–100 times more biologically active in H2 production
[Fe-Fe] hydrogenases more sensitive to O2
[Fe-Fe] hydrogenase requires additional enzymes for assembly of its active site HydE, HydF and HydG
New promising development: mono-
metallic proton-reduction catalysts
+ various Fe0 species
DuBois et al. Science,
2011, 333, 863
Beller et al. Chem. Eur.
J., 2011, 17, 6425
Electrochemically
very active
(TOF=100,000 s-1)
Photocatalytically active with
various cheap Fe-complexes
(up to 600 TON with Fe3CO12)
•Catalytic activity not limited
to ‘relatively complex’
binuclear complexes.
•High TON
PS Cat.
TON=
>5500
Eisenberg et al., Angew. Chem.
Int. Ed. 2012, 51, 1–5
PSI-hematite Dye Sensitised
Solar Cell
AAO – anodic aluminum oxide
FTO – fluorine doped tin oxide
Ocakoglu et al, Adv. Funct. Mat., 2014, 24, 7467–7477
I-V Characterististic of PSI DSSC
Ocakoglu et al, Adv. Funct. Mat., 2014, 24, 7467–7477
Biohybrid PSI-LHCI-based Photoanodes
PSI-TiO2
PSI--Fe2O3
AAO FTO
PSI--Fe2O3
Ocakoglu et al, Adv. Funct. Mat., 2014, 24, 7467–7477
PSI-DSSC produces H2 at a high rate
744 µmoles H2/mg Chl/h
Ocakoglu et al, Adv. Funct. Mat., 2014, 24, 7467–7477
What’s next for the biohybrid
H2 production?• Use the most robust, high light tolerant forms of PSI as the
nearly perfect (IQE=100%) light harvesting/charge separating
non-toxic green module
• Use cheap to produce, earth-abundant stable synthetic metal
catalysts for tight electronic coupling with natural and artificial
light harvesting modules and semi-conducting electrodes
• Use of O2-tolerant H+/CO2-reducing enzymes in tandem with
PSI for production of solar fuels
• Molecular wiring and "smart matrix" nanoengineering of
biohybrid electrode components (minimise e- diffusion &
wasteful back reactions, maximise solar energy capture and
conversion)
• Smart interfacing of the modules to match energy levels,
manage PCET and provide increased stability of the modules
Fully Synthetic Devices
Loll et al., Nature, 2005
YZ
Em+1.21 V
H+
Mn complex
e-
at pH 5.5
overpotential
= 300 mV
O2
TOF per O2~400/s (Mn4O5Ca/YZ)
100/s complete PSII Need to do equally well or better...
H2 formation
or CO2 reduction
Must do better than PSII if want
one photon/one electron process
for H2 formation or CO2 reduction.
or
Use 2 photons per electron energised
Impressive TOF (measure of activity) of 301/s (PSII’s WOC TOF=100-400/s)
TON (measure of stability) of 8,360 (also not too bad)
BUT: Rare element...
A molecular ruthenium catalyst with
water-oxidation activity comparable to that of PSII
Duan et al. (2012) Nature Chemistry, 4, 418–423
Main Challenges: Integration into a Smart Matrix
And Interfacing within Solar-to-Fuel Nanodevices
Selected synthetic WOCs (a-d)
Selected synthetic PRCs (e-g) Barber and Tran (2013) Interface, 10, 20120984
and refs therein
[Mn3CaO4]-clustersCo4O16 with
[PW9O34] polyoxometallate ligands
Nocera CoPiAgapie et al. Christou et al. Hill et al.
Pickett et al. Ogo et al. Dubois et al.
Photoanode
nanowires of
Barber and Tran (2013) Interface, 10, 20120984
and refs therein
Fe-Fe
molecular HECMesoporous InP
electrode
pol. fosforek indu
Si/
Mo
S2
ph
oto
ca
tho
de
Connecting pieces...
Towards Fully Integrated Solar-to-Fuel Devices
Possible Configurations
Must consider: (1) matching energy band gaps, (2) minimising charge
recombination, (3) achieving high TOFs and TONs of the catalysts.
Large band gap semiconductors can be
used without (a) or with electrocatalysts
Cat1 and Cat2 (b).
Two narrow band gap semiconductors
could be wired in a Z-scheme tandem
configuration (c).
Prototypes for Macroscaling?
Biohybrid PSI-based DSSCKargul, Ocakoglu et al, Adv. Funct. Mater., 2014, in press
Self-renewable
synthetic CoPi or
NiFexOy Nocera’s
WOCs:
7.8% solar-fuel
quantum efficiencyReece et al (2011)
PEC of tandem
semiconductor
photoelectrodes
Grätzel cell-type
It is happening...
Biohybrid TiO2-[Fe-Fe]H2ase PECHambourger et al (2008)
Leonardo’s Dream
Cheap electrolysis by day Fuel Cell at night
Possible solution?...
“If the leaf can do it, we
can do it”
It’s just chemistry...
Jules Verne’s Dream (1875)
“I believe that water will one day be used
as a fuel, because the hydrogen and
oxygen which constitute it, used
separately or together, will furnish an
inexhaustible source of heat and light. I
therefore believe that, when coal
deposites are oxidised, we will heat
ourselves by means of water. Water is
the fuel of the future”
Inspired by Nature...
Reece et al. (2011) Science, 334, 645
O2 evolving catalyst (WOC): Co(IV)-oxo-borate*
H2 evolving catalyst (PRC): NiMoZn alloy wafer
photosensitizer: 3jn-amorphous-Si
*self-assembling, self-renewable cobalt catalyst, operating at neutral pH and RT
