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Department of Chemistry and Chemical BiologyHarvard University
Artificial Leaf and Bionic Leaf
Fuel and Food Sunlight, Air and (Any) Water
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day
“2H2” + CO2
biomass
night
O2 + “2H2”
2H2O
NADPH
Photosynthesis is a Two-Step Process
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Solar hn
Energy out
2H2O
O2
O2
4H+ + 4e– ( CH2O )n
CO2
CO2
energy storage hydrogen storage
Two Step Process to Achieve Complete Artificial Photosynthesis
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2H2O → O2 + 2H2 (4H+ + 4e–) Eo = –1.23 V
Go = –nFEo
Water splitting to furnish H+/e– (H2) is thermodynamically uphill:
Thermodynamics of Fuel Formation
CO2 + 8H+ + 8e– → CH4 + 2H2O
Eo = 0.17 V
3CO2 + 18H+ + 18e– → i-C3H7OH + 5H2O Eo = 0.09 V
4CO2 + 24H+ + 24e– → i-C4H9OH + 7H2O Eo = 0.11 V
5CO2 + 30H+ + 30e– → i-C5H11OH + 9H2O Eo = 0.08 V
CO2 + 6H+ + 6e– → CH3OH + H2O
Eo = 0.03 V
Chaplin and Wragg, J. Appl. Electrochem. 2003, 33, 1107
CO2 reduction with hydrogen to fuels is thermoneutral:
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day
“2H2” + CO2
biomass
night
O2 + “2H2”
2H2O
NADPH
The Light Reaction
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Self Healing Water Splitting
But how can sunlight drive these catalysts?
Two catalysts: one to split water to oxygen, the other to take the
leftover protons and electrons to make hydrogen
3-metal alloy, NiMoZnor Co-P(6%) alloy
2H2O O2 + 4e– + 4H+
2H2
Co phosphate oxide
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Self-Healing Enables …
operation under benign conditions and with any
water source(Boston Harbor, Charles River, waste
water, puddle from the ground)This opens up new opportunities:
facile construction of integrated devices
interface with bioorganisms
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Co-OEC
NiMoZnHER catalyst
OER catalyst
400 500 600 700 800 900 1000
Wavelength / nm
0.0
0.2
0.4
0.6
0.8
1.0
Qu
an
tum
Eff
icie
ncy
top
total
middlebottom
• Only coatings – no wires• Works at solar flux• STH of 12.8%
⊕⊖×4
H2
O2
Joep PijpersSENER
Steve ReeceLockheed Martin
Casandra CoxBASF
Tuncay ÖzelApple
The Artificial Leaf Wireless Buried Junction
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day
“2H2” + CO2
biomass
night
O2 + “2H2”
2H2O
NADPH
The Dark Reaction
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Photosynthetic MembranePS I and PSII Replaced with the Artificial Leaf
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Bionic Leaf 1(Water Splitting + Carbon Fixing Organisms)
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Natural Photosynthesis → All Artificial Photosynthesis
Photosynthesis
GAP = glyceraldehyde-3-phosphate
Replace PS
H2
Renewable H2
?
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The Bionic Leaf
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Re-engineered R. eutropha for Isopropanol Production
wt R. eutrophaconverts acetyl-CoA to biomass and polyhydroxy-butyrate (PHB)
R. eutropha 2133-pEG12 Plasmid pEG12 expresses four genes
• phaA (ketothialase)• ctf (acetoacetyl –CoA
transferase)• adc (acetoacetate
decarboxylase)• adh (alc. dehydrogenase)
that redirects acetyl-CoA to the synthesis of isopropanol
Chris GagliardiLEK Consulting
Joe TorellaBoston Consulting
Chong LiuAsst Prof
UCLA
Brendan ColónAmazon
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Energy Efficiency Calculation
Gibbs free energy of CDR x moles of product
electric energy input for H2 productioncharge passed x voltage for water splitting
helec = DrG
o x N
C x Eappl
4CO2(g) + 5H2O(l) C4H10O (l) + 6O2(g)
DrGo (kj mol–1 ) Eappl (V)
For isobutanol:
+1951
N(mol)
8.98 × 106
DrG (kj)
1.56
C(Coul.)
2510 2.0
C x E (kJ)
5.02
helec
31%
for an 20% PV, 6.0% SFE
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Bionic Leaf is Ten Times Better than Natural Photosynthesis
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C10+ Fuels
4 5 60
25
50
75
100
Fatty acid chain length
FF
A c
on
c. (m
g/L
) TE alone
BfTES
7 8 9
CpFatB1
10 11 12 130
10
20
30
40
50
Fatty acid chain length
UcFatB2
acetyl-CoA
Initial Condensation
Fatty Acid
Synthesis
NADP+
NADPH
NADP+
acyl-ACP
NADPHfabB
fabF
Glu PEP
Central Metabolism
thrAfrBC ilvAfr
propionyl-CoAPropionateprpE
H2OACP
TE
Fatty acid
*
* *
*
*TE+ 100mM
propionate
fabH
4 C initially, then add 2 C at a time
medium chain FA
selectivity by altering
thioesterase
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Haber-Bosch process: • Energy intensive: 1~2% world energy supply• High CO2 emission: 3~5% world natural gas use
N2(g) + 1.5CH4 + 1.5O2 → 2NH3(aq) + 1.5CO2(g)
Nitrogen: Another Biogenic Element in Air
Nitrogen Fixation Important as an Energy and Food Target
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Bionic Leaf 2(Water Splitting + Carbon/Nitrogen Fixing Organisms)
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Steps 1 and 2: (1) Split Water and (2) Fix H2 with CO2 to Make Internal Cellular Energy Supply for Microbes
Solar
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Step 3: Microbe Uses Stored Energy and Hydrogen to Make Ammonia
Nitrogen fixation is an energy intensive process:
N2 + 8H+ + 16ATP + 8e− → 2NH3 + H2 + 16ADP + 16Pi
This approach circumvents down regulation
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A Living Biofertilizer
P
PP
Kelsey SakimotoKula Bio
bioplastic
polyphosphate
Chong LiuAsst Prof
UCLA
Solid
Biomass
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Microbes Exposed to 15N-Enriched N2 after PPT Addition
* H−CON(CH3)2 as internal standard
H−14NH3+: t, 6.95 ppm. J1
NH = 50.0 Hz
H−15NH3+: d, 6.91 ppm. J1
NH = 72.7 Hz
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Can Determine TOF and TON from Acetylene Reduction
C2H2 reduction into C2H4:
GC 127 ± 33 µM C2H2 ∙ h−1
~12 mg/L Ntotal per day
1.0 OD600:
2.8 × 108 mL−1 (flow cytometry)
TOF = 1.4 × 104 s−1 per cell
5000 MoFe protein per cell(Eur. J. Biochem, 1995)
~ 3 s−1 per MoFe protein
N2 + 8H+ + 16ATP + 8e− → 2NH3 + H2 + 16ADP + 16Pi
TON:
3.1 × 109 per cell (5-d)
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• ~150% increase in radish (model crop) yield with biofertilizer
• Biofertilizer revitalizes degraded soil, restores soil fertility and biological activity for better plant growth
• Reverses damage to agricultural soils
no biofertilizer w/ biofertilizer
A Living Biofertilizer
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Lettuce and Sweet Corn (Midseason)
Synthetic100% Urea-Ammonium-Nitrate
KM850% UAN + 50% KM8
No Fertilizer
Estimated KM8 delivers at least 60-65 lb N/acre
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• Carbon neutral:Producing synthetic N-fertilizer emits 245 million tons CO2/year
• Carbon negative: This is a CO2-negative fertilizer … after H2 withdrawn from PHB, carbon left behind in soil
A Carbon Negative Fertilizer
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Average US Farm: Sequester 16K lb CO2
Eliminate 125K lb CO2
Note: Assumes 400 acre farm with 65 lb/acre N demand for 26,000 lb N farm demand
=
KM8 sequesters 16,000 lb CO2 H-Bosch emits 109,000 lb CO2
–16,000 lbsequestered CO2
1 farmusing KM8
109,000 lbemitted CO2
1 farmusing Haber-
Bosch
+ runoff & NOx
KM
8
KM8 CO2 sequestration per lb N –0.614 lb CO2 / lb N
Total annual farm N demand26,000 lb N / year
=
H-Bosch CO2 emissions per lb N+4.2 lb CO2 / lb N
Total annual farm N demand26,000 lb N / year
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Sunlight + Air + Any Water
Distributed Fuel (C neutral) and P|N Fertilizer (C negative)
Negative carbon budget my be large when high efficiency carbon fixation (i.e., fast biomass) is interfaced to agriculture
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With Much Gratitude
Kat Taylor Tom Steyer
All funding for this project provided by a 4-yr gift from ….