Description: A Regenerative Fuel Cell (RFC) is an electrochemical energy storage device that operates like a rechargeable battery with the potential to store significantly more energy with lower mass for long-term energy storage needs. An RFC consists of a fuel cell, an electrolyzer, fluid processing system and a reactant storage system. The fuel cell converts chemical potential energy into electrical energy; fuel cell consumes hydrogen (H2) and oxygen (O2) gasses to produce electricity, heat, and water. When powered by an external source, such as a photovoltaic array, the electrolyzer produces H2 and O2 gasses from the water produced by fuel cell stack. Fundamental thermodynamics limit the round-trip efficiency of this process to below 60%. For this project, both the fuel cell and the electrolyzer use the proton exchange membrane (PEM) electrolyte technology. The RFC Project will develop RFC technology to provide energy storage for spaceflight applications including in-space, lunar surface exploration, and surface exploration of other planetary bodies. Future exploration missions, including human missions to the Moon and Mars, are expected to have a variety of longer-term energy needs that cannot be met using batteries for energy storage. For missions with larger energy storage requirements, RFCs offer equivalent energy storage for lower mass. An RFC energy storage system can provide power in locations near humans where nuclear power is not an option. It can also provide power to Lunar Landers, ISRU applications, Exploration Rovers, and Lunar Habitation. The RFC is versatile enough that it can provide power for longer-term operations, such as Lunar nights, and will enable missions to operate in harsh environments such as permanently shadowed crater areas.

Benefits: Power and energy storage are key commodities needed for space exploration, including that of the lunar and other planetary surfaces. Existing energy storage technologies (including projected Li-ion battery systems) do not have a sufficiently high specific energy (W•h/kg) to satisfy lunar surface mission energy storage requirements within available mission mass budgets. Energy storage technology advancements are needed to improve specific mass, specific energy, and overall energy storage system efficiency to reduce the mass and size of space power systems and resulting launch mass and overall space system volume. These improvements increase the probability of achieving mission objectives and/or reduce mission costs. Some advanced energy storage technologies are needed to enable missions such as surface mobility or nighttime operations and provide for operation in extreme environments, such as lunar night. Current energy storage technologies, such as Li-ion batteries, are insufficient for NASA Lunar exploration missions due to the length of the lunar night and resultant energy needed to operate through it. - Regenerative Fuel Cells (RFCs) can provide an enabling technology suite for sustained and reliable electrical power for surface and near-surface missions where PV/battery or Nuclear options are not feasible. - RFCs offers up to 3.4X energy storage for the same mass as batteries. Higher specific energy (W·hr/kg) for high energy applications where fully packaged battery system become too massive. -The Regenerative Fuel Cell (RFC) Project will develop RFC technology to provide energy storage for spaceflight applications including in-space, lunar surface exploration, and surface exploration of other planetary bodies.