Human Persistence in Space enabled by Artificial Photosynthesis

Key Technical Challenges: Sourcing materials to fabricate into functional cells of >10% efficiency and also the stability of those devices reaching desired parameters, ~1000 hours of operation for feasibility. There is no standard test criteria for lifetime of these devices due to their novelty and hence we will generate a failure modes and effects analysis (FMEA), utilizing industrial best practices and legacy fuel cell data to determine lifetime goals, but target of 1000 hours initially.\nApproach/Research Plan: Construct glassware electrolyzer and demonstrate feasibility H2/O2 production using a commercial solar cell; Obtain III-V candidate materials to absorb incident light and metalize these photoelectrodes with three candidate metals for testing; Develop high efficiency PEC prototype using the III-V absorber reproducing literature values; Demonstrate effective silanization of the photoelectrodes; and, Demonstrate >2x lifetime improvement for silanized samples over control up to 1000 hours of H2 production and 2x improvement in degradation rate over that time interval.\nDifferent/Complementary: Our approach involves the utilization of space photovoltaics based on III-V materials (e.g. GaAs) that have demonstrated among the highest efficiencies of any PV material and have been utilized as successful PECs. \nNext Step: We will look to further develop the concept of an adaptable, in-space PV/on-surface PEC system that enables spacecraft to operate in a dual mode.

Goal: To determine the feasibility of a novel photoelectrochemical cells (PEC) using photovoltaic-like devices (GaAs with metal oxide electrodes) for lunar surface power.\nCapability Need/Knowledge Gap: A PEC has advantages 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%. This effort will heavily leverage existing expertise in the GRC Photovoltaics and Electrochemical Systems Branch among the few groups nationally that has long-standing expertise in fuel cells, electrolyzers, III-V materials and photovoltaics, which are critical to the successful development of a PEC. \nState-of-the-Art/Knowledge: The relative state of the art in this program concerns several distinct areas including photovoltaics, power management electronics, and water electrolysis. 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 when 19% was reported.

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