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New fuel cell could enable electric aviation | MIT News (news.mit.edu)

submitted 5 months ago by Wahots@pawb.social to c/energy@slrpnk.net

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[–] perestroika@slrpnk.net 7 points 5 months ago* (last edited 5 months ago) (1 children)

Thanks for the tip, both the popular and scientific article are interesting.

Short summary of the pros and cons:

energy density: 3 x better than lithium ion
power density: really poor (if they raise their power density by 10 times, it will suffice for cruising, takeoff will require supplementary high-current batteries)
exhaust: sodium oxide (caustic), converted by moisture in air to sodium hydroxide (caustic), converted by CO2 into sodium bicarbonate (harmless) --> this is a tech for cruising up high, not for takeoff or flight above settlements ("don't stick unprotected head into exhaust stream, risk of losing eyes")
climate impact: positive, removes CO2 from air
operating temperature: reasonable (about 100 C)
mass production of sodium: doable, but somewhat messy
fire safety: sodium burns just as bright as lithium, nothing cheerful here

My personal conclusion: currently, this is a potential military technology ("electric cruise missiles / strike drones with 500 km range"), likely won't reach passenger or cargo aviation soon due to lack of sodium handling infrastructure.

[–] hydroxyl@freeradical.zone 5 points 5 months ago (1 children)

@perestroika @Wahots thanks for the breakdown! a short question: so military aviation applications need less km range or is it something else that leads to the conclusion of military tech direction. it's very frustrating seeing the hard work we make for the benefit of our energy community as researchers ending up in military applications :tiredcat2: :firepoop: how can we avoid this?

[–] perestroika@slrpnk.net 5 points 5 months ago* (last edited 5 months ago) (1 children)

It's not the range. With this technology, it's just the combination of fuel and exhaust that makes it unlikely to reach peaceful applications sooner.

A user of this technology must be willing to tolerate (and cause) considerable inconvenience just to increase the range of their electric aircraft.

Fuel distribution would be an annoying but surmountable problem. Not the easiest, but doable. Sodium needs to be stored either in mineral oil or inert gas. Otherwise it will spontaneously oxidize quite fast. Airports would need sodium warehouses with specialized equipment (either oil baths to submerge it or some kind of lockers with an unbreathable atmosphere). Trucks with the same kind of equipment would be needed to deliver the stuff. Maybe a bottle system could be devised, whereupon sodium is solid in a bottle and the bottle is heated above 100 C to pour it out.

Fuel production efficiency would be a problem. I don't know the efficiency of sodium production, but intuitively this is likely to be around 80% (plus road transport). Charging a battery from the grid is more efficient, so the user of this technology must either have cheap electrical energy (this might be true in future with lots of renewables) or be willing to ignore the cost of energy (military users will do that already now, just promise them a bit more flight range).

Finally, public debate about a caustic exhaust stream is likely to be non-trivial. I predict that people will be quite worried about the direct effects of NaO and NaOH air pollution - it's one of those things which is clearly health negative, even if climate positive. Convincing people that it's safe will require studies about how quickly NaO turns into NaOH, and how quickly the exhaust stream neutralizes and becomes safe. Unsurprisingly, military users are pretty unconcerned about being health negative - most of their tools are like that.

[–] hydroxyl@freeradical.zone 3 points 5 months ago

@perestroika thank you again for your input. i knew that metal-air batteries/cells are like very novel but it seems they are unfeasible beyond TRL 3 for now. and the point on the military ignoring the energy expenditures is very valid actually. thanks again :blobheart: