Note to Elisabeth

1. 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.

2. Photosynthesis Natural Leaf Artificial Leaf H2O sun + water H2O energized wireless current ⊖ ⊕ ⊖ ⊕ O2 O2 (4H+ + 4e–) H2 NADH “Natures H2” solar fuel

3. 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)

4. Artificial Leaf Challenges Oxygen catalyst OER Catalyst Protective layer ITO Silicon Si Hydrogen catalyst 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

5. 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.

6. An Artificial Leaf That Works OER catalyst Co-OEC 1.0 0.8 total 0.6 Quantum Efficiency top middle 0.4 bottom 0.2 0.0 400 500 600 700 800 900 1000 Wavelength / nm HER catalyst 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

7. 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.

8. Traditional PEC Deviates from Principles of Photosynthesis Catalyst and light harvester are one an the same: p-n PEC (PV electrochemical load) electrolyte n-SC and HER OEC 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

9. 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.

10. 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

11. Roll-to-Roll Processing Chemical Vapor Deposition (CVD) exhaust precursor B precursor A CVD – high thru-put manufacturing (1000 m/hr): automotive glass all e-glass displays desorption PV film growth reaction adsorption Professor Roy Gordon Harvard Corning Willow (flexible) Glass

12. 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.

13. 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 needed … independent of subsequent (photo)catalytic transformation H2 “stuff” • Allows photomaterial to be decoupled from challenging multi-PCET catalysis needed for solar fuels generation • Engages expertise of a wider community (e.g., organic, organometallic chemists) in the energy problem H2O