In preparation for future Lunar and Martian surface operations, NASA is seeking viable methods of storing energy captured by solar panels for use in times of limited solar energy availability. Currently used Li-ion batteries, while sufficient for short-term energy discharge cycles, are not optimal for the Moon’s 29.5 day diurnal period as their energy storage capacity scales linearly with system mass.
Regenerative Fuel Cells (RFCs) offer an alternative method for storing electrical energy with more favorable scaling metrics, combining electrolyzers (split water into H2 and O2 gas in times of energy surplus) with fuel cells (generate energy during energy deficits by recombining gases into water). RFCs have a mass advantage over batteries for Lunar operations, with energy densities of 400 to 550 Wh/kg.
PEM electrolyzers produce saturated gases which, if the temperature drops below dew point, may result in condensation that can freeze and damage fluidic connections in the system. Thus, any solution that incorporates RFCs requires a dedicated dehumidification subsystem.
To meet this challenge, Lynntech proposes a two-stage water removal/reclamation system that involves traditional compression and phase separation, as well as cascading Metal Organic Framework (MOF) based desiccant beds with vacuum heated water reclamation/regeneration. Lynntech intends to design a system with 2 independent canisters with multiple in-series MOFs each for simultaneous absorption and regeneration. One MOF canister will dehydrate water while the other regenerates captured water to the H2O tank. These canisters then switch, resulting in continual gas dehydration and water regeneration throughout the operating cycle.
Lynntech will team up with Framergy, experts in MOF development and optimization, to design this hybrid MOF-based approach to RFC dehumidification that exceeds NASA’s desired mass recovery rate to decrease overall system mass.
Lynntech’s development effort will enhance and expand the capabilities of RFCs in NASA application by optimizing system energy density while avoiding proportionally increasing system mass. Such advancements greatly increase the viability of long-term missions to asteroids, planets, moons, or any other operation that experiences cyclic exposure to sunlight. Additionally, improved RFCs may be used for life support during In Situ Resource Utilization operations, providing H2O or O2 for human consumption.
Long-term solar-powered flight may greatly benefit from lightweight solutions to increase efficiency in RFC systems. The addition of a MOF-based regeneration system increases the mass recovered throughout each cycle, decreasing the initial on-board water mass required and optimizing system energy density.