Fuel cells and electrolyzers for space applications: for energy storage to propulsion/deorbitation
Regarding applications for space, two main groups of technologies and applications can be distinguished regarding hydrogen field: gas production (hydrogen and oxygen), and power generation. Firstly, for gases generation, reforming of bioethanol and PEM electrolysis are possible choices for hydrogen production for terrestrial plants related to space activities. Secondly, regarding power generation with fuel cells, different applications are possible.
Proton exchange water (PEM) electrolysis is an electrochemical process in which pure water split up into hydrogen and oxygen by means of electricity using a polymer electrolyte membrane as a medium of transfer.
Electrolysis process is the most suitable technology for gases production on board. Even if the overall electrochemical reaction is the same as for a terrestrial plant, some operational and design details have to be modified in order to fulfil with on orbit conditions.
Hydrogen produced by electrolysis is essential for space missions because it is the main fuel used for propulsion of spacecrafts during launch and it can also be used for on orbit propulsion and deorbiting at the end of the operative life of the spacecraft.
On the other hand, the other product gas of the electrolysis process, oxygen, is necessary for life support in manned missions, like in the International Space Station.
Power generated by fuel cell systems can be used for many aerospace applications:
- Stationary back–ups
- Military/ Aeronautic auxiliary power units (APUs)
- Unmanned aerial vehicles (UAVs)
REVERSIBLE FUEL CELL SYSTEM
Reversible fuel cell system consists of a stack that operates in both ways:
- Fuel cell mode: the stack consumes hydrogen and oxygen and produces water and power.
- Electrolyzer mode: when power is supplied to the stack, it consumes water and produces hydrogen and oxygen.
REGENERATIVE FUELL CELL SYSTEM
A regenerative fuel cell system consist of two different stacks (one fuel cell and one electrolyzer) connected to three storage tanks (for hydrogen, oxygen and water) that operate in a closed loop.
This kind of systems can be used as auxiliary power supply for spacecrafts (satellites, rovers, etc.).
It could be a possible substitute for current batteries presenting a mass saving and higher energy density that improves with the increase of the power level.
Innovations & Advantages
- Production of hydrogen by electrolysis for launchers is an environmentally friendly process.
- Replacing batteries by fuel cells in satellites leads to an important mass saving.
- Fuel cells presents a higher energy density than batteries.
- Hydrogen produced by a regenerative fuel cell system on a satellite could also be used for propulsion and deorbitation manoeuvres.
Current and Potential Domains of Application
- Hydrogen production for launchers
- Propulsion/deorbitation by water electrolysis
- Power for launchers (by means of fuel cells)
- Power for telecom satellites (by means of regenerative fuel cell system)
- Combination of propulsion and power generation for telecom satellites (by means of regenerative fuel cell system)