Human Persistence on the Lunar Surface Enabled by Artificial Photosynthesis

Goal: To determine the optimum device architecture for a visionary hybrid photovoltaic/photoelectrochemical cell (PEC). Capability Need/Knowledge Gap: The objectives are to demonstrate the feasibility of a PEC device for extra-terrestrial artificial photosynthesis by constructing engineering prototypes and determining durability through longevity testing. In our FY19 CIF proposal we described the advantages a PEC holds over the current state of the art by reducing complexity, the number of active elements, and the weight of a photovoltaic-driven electrolysis system by over 50%. The relative state of the art in this program concerns several distinct areas including photovoltaics, power management electronics (PMAD), and water electrolysis cells. The product of these three contributors determines the “solar-to-hydrogen” (S2H) conversion efficiency of the system, for which we typically find 14%. The highest S2H metric for a direct photoelectrochemical cell increased very recently with 19% reported, using III-V materials of space solar cells. Key Technical Challenges: Identifying and fabricating the hydrogen and oxygen evolution catalysts, as well as the deposition of those catalysts on the front and back of existing solar cells. Approach/Research Plan: (1) Identify and procure candidate metal oxides targets (raw materials) and obtain solar cells; (2) Deposit combinatoric metal oxides, classify optical transmission, durability vs alloy content and silane deposition; (3) Metal oxide candidate cutdown to 3 candidates, deposit on solar cells and achieve efficiency of 10%; and, (4) Improve PV efficiency to 20% and PEC efficiency to 10%, extend lifetime to 1000 hours. Vapor deposition techniques will be used to create material alloys. Machine learning can be used to gain fast insights on these materials. We will explore the use of organofunctional silanes as surface energy modifiers. We will source triple junction III-V solar cells from various manufacturers with and without front contacts - in order to allow our processing into PECs by deposition of our metal oxide catalysts. Next Step: To further this technology, new protection schemes need to be developed. For PV/PEC arrays on lunar landers, the radiation exposure is not great when the flight time is considered. A fiberglass webbing could hypothetically be embedded on the cells to provide breakage.

PECs have been explored since the 70s, but only recently have high efficiencies been achieved because typical solar cells are not energetically favorable for electrolysis of water. Other researchers have demonstrated the feasibility of devices from an efficiency and performance perspective, but lifetimes – of the order of 100 hours – are fundamentally limited by electrode corrosion from the caustic electrolyte. There is precedent for exploring the use of organofunctional silanes as surface energy modifiers, including previous work on enhancing durability of metal oxides (indium oxide and zinc oxide) by the PI, as well as thin film solar cells.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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