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Nanostack printing for materials research

Periodic Reporting for period 2 - NANOSTACKS (Nanostack printing for materials research)

Reporting period: 2021-08-01 to 2023-01-31

Man-made fuel cells have a bad energy-efficiency, i.e. they waste two thirds of the energy as heat when they convert hydrogen to electrical energy. Moreover, they need expensive palladium-based catalysts because all the other catalysts are irreversibly poisoned by molecules in ambient air. Hydrogenases that are Nature’s fuel cells convert chemical energy very efficiently into electrical energy, and they do that with cheap iron oxide-based catalysts. We want to find out if we can manufacture a fuel cell that is as efficient as Nature’s fuel cells, and that uses a cheap catalyst. That is important for society, because regenerative electrical energy is generated when the wind blows or when the sun shines, but two thirds of that energy gets lost, when stored in a state-of-the-art fuel cell. Batteries are much more efficient in storing electrical energy, and by now fuel costs for an electrical car are cheaper than costs for diesel fuel because also a diesel engine wastes 70% of the chemical energy that drives the car. But batteries have a problem with their energy-density: It is too expensive to store the huge amount of energy in a battery that is needed when the wind doesn’t blow. In addition, electrical cars need heavy and expensive batteries, and still can’t drive as far as a gasoline powered car. An energy-efficient fuel cell would solve these problems: Huge amounts of electrical energy could be stored in high density for dark winter days when the wind doesn’t blow. And if combined with a small battery an efficient fuel cell would outperform a gasoline powered car or airplane. Engineering a fuel cell as Nature does is difficult, though. Energy converting enzymes all use the same basic trick: similar to a marble run, they fast lead electrons down a predetermined pathway of redox centres, and, thereby, prevent the electrons from recombining with the left-behind proton which would dissipate the electron’s energy as heat. To build such a gradient of redox centres is difficult. Neighbouring redox centres must be distanced a mere 2nm from each other to have the electrons jumping layer by layer down a gradient of redox centres as they do in a hydrogenase. We use a recently invented multi material nano3D printer to print such layers as nanostacks, and we want to nano3D print >15.000 electrically connected twin nanostacks per glass slide. One of the twin nanostacks reports an energy-rich electron via a printed LED, while the other twin nanostack generates these energy-rich electrons via a printed solar cell or fuel cell. Thereby, we want to do materials evolution: printing many different nanostack variants, and selecting improved solar cells or fuel cells.
nano3D printer: In the first reporting period we advanced our nano3D printer to an automated robot that uses a gripper arm to replace acceptor and donor slides. The acceptor slide receives the printed materials – typically as spots with some 100-150µm in diameter and some 5-100nm in thickness that are transferred due to a single laser pulse. The donor slides have one type of to-be-transferred-material metered onto a polyimide layer, with a typical layer thickness of some 0,5 to 1µm. We found and analysed meanwhile more than 70 different materials that could be transferred with single laser pulses in order to get a tool box that could be used to combinatorially print all kinds of nanostacks. We estimate that the nano3D printer meanwhile reached TRL8.

nano3D printable materials: fall into several categories:
1. Polymers that serve as “solid solvents”, i.e. when melted by heat or solvent vapour they support a chemical reaction just like a normal solvent does.
2. Amino acids that are embedded within “solid solvents”. These are used to first structure an acceptor slide with >20 different amino acids as solid materials, and then simply by melting elongate growing peptides in the array format to synthesize peptide arrays.
3. Other chemical building blocks embedded within solid solvents that similar to peptide synthesis are used to synthesize many different light absorbing molecules.
4. OLED materials, e.g. emitter materials, electron transport materials, hole transport materials that can be used to nano3D print diodes, LEDs, batteries, solar cells or similar.
5. Polymers with a very high density of reactive groups. Such polymers can react after or before nano3D printing with many different types of small molecules, e.g. to equip them with different types of redox centres, or metal centres.
6. Self-immolative polymers that start to depolymerize into small monomers that simply evaporate once a protecting group at the polymer’s ends is removed, e.g. by light or by acid. We want to use these self-immolative polymers as a carrier material for difficult-to-print-materials.
6. Finally, nanoparticles are printed in order to get lines or spots that serve as electrodes, conductors, isolators, capacitors, coils, semi-conducting LED layers etc.

Microstructured materials: A second line of experiments successfully manufactured microstructured pillars in order to define nano3D printing also in x,y-direction. Most interestingly, we identified some materials that could be used for reversible microstructuring. Unfortunately, due to corona restrictions, LEUVEN could hire its two PhD students only recently, which lead to some minor delays in the manufacturing of other microstructured acceptor slides.

nano3D printed functional entities: Next on the list of experiments will be to use the different materials that were identified in the first reporting period to nano3D print LEDs, conductors, insulators, and capacitors, and test them for performance. These experiments are due in the second reporting period.
High density peptide arrays: Commercialisation of nano3D printed peptide arrays by SME PEPperPRINT is well on track. The only missing thing is milder conditions for printing Fmoc-Arg-OPfP, which currently brings down the quality of arginine-containing peptide arrays, and, thereby, delays commercialisation of these arrays. When compared to peptide arrays that are produced with the peptide-laser-printer, these arrays have an estimated 5-fold higher density of synthesized peptides, and they are an estimated 10-fold cheaper per synthesized peptide. To our knowledge, this type of peptide arrays is unrivalled.

High density arrays with fluorophores: An achievement that was not foreseen in the NANOSTACKS proposal was the finding that we can synthesise many other chemicals beyond peptide synthesis.

nano3D printing materials: During the first reporting period we found a surprising high percentage of nano3D printable materials. Moreover, when using a donor-heating-device we can obviously nano3D print materials that couldn’t be printed at room temperature.

nano3D printed nanostacks that function as LEDs or similar: These experiments will be done in the second reporting period.
Assembled nano3D printer