Note to Elisabeth
The artificial leaf works the same functional way as a real leaf. Importantly
the membrane is “buried” and end-capped with cofactors (catalysis) to do
water splitting.
The same is true for the artificial leaf.
Photosynthesis
Natural Leaf
H2O
NADH “Natures H2”
sun + water
H2O
energized
wireless current
⊖
⊕
(4H+ + 4e–)
Artificial Leaf
O2
⊖
⊕
H2
solar fuel
O2
Note to Elisabeth
A stand alone device had never been made (despite claims by others –
who are always trying to shoot down the artificial leaf)
The naysaryers point to the paper in the next slide. But the concept is
shown at the beginning of the paper only as a schematic. It was never
achieved for the reasons listed in red. I even highlighted the text where it
syas that they could not make a stand alone device)
Artificial Leaf Challenges
Oxygen catalyst
OER Catalyst
Protective layer
ITO
Silicon
Hydrogen catalyst
Si
HER Catalyst
• Need conc base for catalyst,
but Si corrodes in conc base
• But Si dies in conc base
• Thus need to externally wire
anode to Si triple junction,
above device not achieved
Note to Elisabeth
The following device works because the system operates simply in water
(not concentrated base or acid). This is because the water splitting
catalysts are able to operate out of water without corroding.
They actually break down but the real invention is that they self-heal. This
we can work in water and make the stand alone artificial leaf.
An Artificial Leaf That Works
1.0
Co-OEC
Quantum Efficiency
OER catalyst
0.8
total
0.6
top
middle
0.4
bottom
0.2
0.0
400
HER catalyst
500 600 700 800
Wavelength / nm
NiMoZn
• commercial solar cell, Xunlight
• cell voltage high enough for OER
• 4.7% efficient (6.7% solar cell)
• higher efficiencies possible, simply use higher efficiency PV
900 1000
Note to Elisabeth
The “buried” junction is different than a regular PEC for the following
reasons. Importantly the band gap does not need to span the chemical
potential (because the PV is buried between conductors)
Also, like in a leaf, the catalysis (cofactors in a leaf) is separated from the
charge separating network (membrane in a leaf, PV in the buried junction).
PECS had been worked on for almost 50 years, and they were never able
to perform water splitting at high efficiency. The new system works, and it
is because it is fundamentally a different PV.
Traditional PEC Deviates from Principles of Photosynthesis
Catalyst and light harvester are one an the same:
(PV
p-n PEC
electrochemical load)
electrolyte
n-SCOEC
and HER
membrane
p-SC and OER
electrolyte
 Because chemistry is in direct contact with chemistry
flatband potential must straddle the thermodynamic
 Likelihood of making a good solar absorber that at the same
time can manage the complicated and intricate 4e–/4H+
chemistry of water splitting is miniscule
Note to Elisabeth
Because the artificial leaf is simply layers, like a hamburger, it opens the
door to high throughput manufacturing. We are now involved with
producing the leaf by CVD methods. This will allow us to simply coat glass
on a production line.
Clas can be processed at ~5000 – 10000 metrs per hour. We are seeking
to “spray coat” the galss on the line with the layers needed for the artificial
leaf. We are working that chemistry out now.
An Artificial Leaf = Fast Food Energy
Top bun
OER catalyst
Co-OEC
Cheese
Hamburger
Bottom bun
HER catalyst
NiMoZn
• no wires, no membrane
• works in any water
• simple engineering
• simple engineering
• just layers
• like a hamburger
Roll-to-Roll Processing
Chemical Vapor Deposition (CVD)
precursor A
exhaust
precursor B
CVD – high thru-put
manufacturing
(1000 m/hr):
desorption
reaction
adsorption
PV film
growth
automotive glass
all e-glass
displays
Corning Willow (flexible) Glass
Professor Roy Gordon
Harvard
Note to Elisabeth
The real advantage of the artificial leaf is you can let H2 bubble out of the
water, collect it, and then use it.
Remember the thermodynamics of H2 to CO2 for almost any fuel is
downhill. This it is a “dark” reaction. You only need light to make H2.
So I do not believe in direct solar to liquid fuels. With the artificial leaf, you
can collect the H2 in another container and then do liquid fuels production.
Alternative Strategy to Traditional PEC Approach
 As in photosynthesis, decouple
thermodynamics of water
splitting (uphill) from
subsequent catalytic chemistry
(thermoneutral)
N2
CO2
CO
.
.
.
 Use photomaterial for what is
“stuff”
needed … independent of
subsequent (photo)catalytic
transformation
H2
 Allows photomaterial to be
decoupled from challenging
multi-PCET catalysis needed
for solar fuels generation
H2O
 Engages expertise of a wider
community (e.g., organic,
organometallic chemists) in
the energy problem