Technion team devises method for on-demand H2 production from water and aluminum for aviation applications
Aerospace engineers at the Technion-Israel Institute of Technology have developed and patented a process for on-demand hydrogen production from the reaction of activated aluminum powder and water for commercial aircraft applications. The hydrogen produced on-board during flight can be used in a fuel cell to generate electric energy for auxiliary power.
In addition to fresh water, the waste water available on-board the aircraft can be used for hydrogen generation. The researchers demonstrated high reaction rates producing about 200-600 ml/min/g Al of hydrogen at a high yield of about 90% was demonstrated. The possibility to use the available waste water leads to high specific electric energy of up to about 850 Wh/kg. The work was reported in a recent paper published in the International Journal of Hydrogen Energy.
One of the main challenges associated with the use of PEM fuel cells on-board an aircraft is the hydrogen fuel storage due to hydrogen’s extremely low density (gaseous state: 0.089 kg/ m3, liquid state: 71 kg/m3). It implies storage as hydrogen gas at very high pressures (350-700 bar) or as liquid at very low temperatures (~20 K) [-253 ˚C]. Furthermore, central storage and long pipelines of elemental hydrogen within the aircraft involve safety issues due to its high flammability and explosion hazards.
A novel method for in-situ and on-demand hydrogen production was developed and patented at the Faculty of Aerospace Engineering of the Technion - Israel Institute of technology, based on activation of aluminum powder to react spontaneously with any type of water at room temperature. … This technology offers a good solution to the challenges mentioned above, namely, high specific energy storage with no actual storage of gaseous or liquid hydrogen. Only activated aluminum powder should be stored, producing hydrogen gas only when needed, according to the rate of its use. Furthermore, fuel cell units with their assigned hydrogen source may be located at the points of need on-board the aircraft.—Elitzur et al.
The spontaneous and sustained reaction between powdered aluminum and water is enabled by a special thermo-chemical process of aluminum activation the researchers developed. The protective properties of the oxide or hydroxide film covering the aluminum particle surface are modified by a small fraction of lithium-based activator diffused into aluminum bulk, allowing water at room temperature to react spontaneously with the aluminum.
The process does generate heat, which the researchers say can be used for a number of tasks, including heating water and food in the galley, de-icing operations, or heating aircraft fuel prior to starting the engines.
According to the researchers, their technology would provide:
- Quieter operations on board an aircraft
- Drastic reductions in CO2 emissions
- Compact storage; no need for hydrogen storage tanks onboard aircraft
- More efficient electric power generation
- A reduction in wiring (multiple fuel cells can be located near their point of use)
- Thermal efficiency (fuel cell generated heat can be used for de-icing, heating jet fuel)
- Reduced flammable vapors in fuel tanks (Inert gas generation)
The researchers estimated that the total mass of such a system, including hydrogen storage and a fuel cell, when using the activated aluminum-water technique, is somewhat lower compared to high pressure hydrogen gas system and somewhat higher than that of liquid hydrogen system. Even though the total mass of liquid hydrogen system is slightly lower, the safety aspect makes a lot of difference.
Aircraft manufacturers, including Boeing and Airbus, have already investigated using onboard fuel cells. Boeing has experimented with them in smaller aircraft, in anticipation of using them on its 787-8, the current state-of-the-art electric airplane. According to the Technion researchers, fuel cells can even play an energy saving role in airline and airport ground support operations when they are on used for systems such as de-icing and runway light towers.
Shani Elitzur, Valery Rosenband, Alon Gany (2017) “On-board hydrogen production for auxiliary power in passenger aircraft,” International Journal of Hydrogen Energy doi: 10.1016/j.ijhydene.2017.02.037