In-flight Hydrogen Production for Aviation
S. Himmelstein | April 28, 2017Technology for producing hydrogen on-board during commercial aircraft flights can support fuel cell operation to generate electricity for auxiliary power. Such a process for on-demand hydrogen production has been developed and patented by researchers from Technion-Israel Institute of Technology.
Hydrogen is produced from water (including waste water on the plane) and aluminum particles. The development eliminates the hydrogen storage problem and could pave the way for less-polluting, more-electric aircraft that replace hydraulic and pneumatic systems typically powered by the main engine from the reaction of activated aluminum powder and water for commercial aircraft applications.
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.
Hydrogen can be produced on-board aircraft from activated aluminum powder and water.
Heat generated during the process can be used to heat water and food in the galley, augment de-icing operations or heat aircraft fuel prior to starting the engines.
Quieter on-board operations and reduced carbon dioxide emissions are additional benefits cited by the researchers.
This sounds very much akin to CCHOD (catalytic carbon being the active agent that overcomes the aluminum oxide, even at oxide stable pH values.) Reaction proceeds best when at 85°C, and is patented. It might be interesting to see if using a small amount of catalytic carbon (CC) could be used to mainly sustain the Aluminum powder reaction that was started using the Li metal doped Aluminum, but later dosing of Al powder does not require "expensive" doping.
I still fail to understand why large rechargeable Aluminum metal anode batteries would not be utilized in the first place, thereby bypassing a number of steps.
In reply to #1
Pound-for-pound how would Al batteries stack up against this process + fuel cells?
In reply to #2
My expectation is that it would be similar in tonnage. One nagging thing about generating hydrogen either way is the possibility of a thermal runaway if reactor is overdosed, improper cooling is taking place, and the hydrogen product is not being taken off by demand as rapidly as produced. This could lead to over-pressure in hermetic enclosed systems, with catastrophic failure. Controls have to be in place in either generation system (that makes hydrogen).
For the aluminum battery, the metal is in the form of a plate anode, and there is electrolytes, cell separator (each half-cell), battery separator that prevents shorting of cells together, and cathode material (carbon, in this battery it stores a negatively charged aluminum complex ion in the interstitial spaces between sheets of graphene (graphitic carbon).
Compare all that with the components needs for a fuel cell battery of the same power output requirement (with similar to same external conditions of operation), and perhaps the mass is slightly less, perhaps due to efficiency, but also due to less required mass of electrodes with fuel cell designs. Offsetting that is the not negligible mass of the bank of hydrogen generation reactors required, and these can be whoppingly massive (by comparison with a battery), especially if they are required to operate at or near water boiling at 1 atm, except they will also likely be operating at elevated pressure.
While I do not have all the design data on either system in front of me, I feel pretty confident in saying the Aluminum battery would take the field in a heads up competition, even though this battery technology is not mature, where fuel cells are very mature, but would be coupled with less mature generation technology, and that is the challenge at hand.
In reply to #3
Good, well-reasoned reply. Thanks.
Another question involves current. There are compact, high-capacity batteries that can sustain a moderate current for a long time, but really can't put out a lot of current for a short time. How does the newer Al tech stack up against fuel cells here? (bear with me, I'm not battery engineer).
In reply to #4
Owing the +3 charge on the Aluminum ion, I would expect current density (and potential) to be quite brisk.