How to make a battery without having to store ugly nasty HCl:
Okay so I said I would probably write more about this, so here goes... If we have an NaCl -> NaOH + HCl battery, we don't specifically need to store HCl, what we need to store is Cl- and H+.
If we could take some other metal like say iron and swing it from Fe(OH)₂ + 2Cl- -> FeCl₂ then we would have a place to sink the Cl- without making a nasty acid. Unfortunately, it's not enough just to store Cl-, we also need to store the H+ of HCl because otherwise every time we charge and discharge, we're going to make H2 and O2 and getting abysmal efficiency.
But if we get rid of the OH group, and go to something that only needs to store Cl-, then we can just store that.
FeCl₂ -> FeCl₃ stores 1 Cl- ion, and the cost of that is 8.81 wh/mole.
FeCl₂ -> Fe(solid) releases 2 Cl- ions, and the cost of that is 84 wh/mole.
3FeCl₂ -> Fe + 2FeCl₃ is balanced without fussing around with OH and H2O.
And this chemistry is typical in iron flow batteries. You can realistically get away with around about 2 moles of FeCl₂ or FeCl₃ per liter of water.
So with 1.5 liters of FeCl₂ turning into 1 liter of FeCl₃, and 55 grams of iron plated off on the electrode, you store about 90ish watt-hours.
So 1.5 cubic meters of FeCl₂ turning into 1 cubic meter of FeCl₃, and 55 kg of iron plated off on the electrode, you store about 90ish kilowatt-hours of electricity.
Unfortunately, FeCl₃ is also a fairly nasty thing which needs to be in highly acidic conditions - and not exposed to oxygen or it will begin converting itself into FeOH gunk. It is not quite as bad as pure HCl but it's still an acid.
Caleb James DeLisle
npub105…t88up
2026-10-05 10:39:03 UTC
in reply to nevent1q…dxxa
Author Public Key
npub10502c8jv0y27jwcwxcq9kd3ph2wg7pt8ycexf5w2fyzythe97w2s7t88upPublished at
2026-10-05 10:39:03 UTCEvent JSON
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"content": "How to make a battery without having to store ugly nasty HCl:\n\nOkay so I said I would probably write more about this, so here goes... If we have an NaCl -\u003e NaOH + HCl battery, we don't specifically need to store HCl, what we need to store is Cl- and H+.\n\nIf we could take some other metal like say iron and swing it from Fe(OH)₂ + 2Cl- -\u003e FeCl₂ then we would have a place to sink the Cl- without making a nasty acid. Unfortunately, it's not enough just to store Cl-, we also need to store the H+ of HCl because otherwise every time we charge and discharge, we're going to make H2 and O2 and getting abysmal efficiency.\n\nBut if we get rid of the OH group, and go to something that only needs to store Cl-, then we can just store that.\n\nFeCl₂ -\u003e FeCl₃ stores 1 Cl- ion, and the cost of that is 8.81 wh/mole.\n\nFeCl₂ -\u003e Fe(solid) releases 2 Cl- ions, and the cost of that is 84 wh/mole.\n\n3FeCl₂ -\u003e Fe + 2FeCl₃ is balanced without fussing around with OH and H2O.\n\nAnd this chemistry is typical in iron flow batteries. You can realistically get away with around about 2 moles of FeCl₂ or FeCl₃ per liter of water.\n\nSo with 1.5 liters of FeCl₂ turning into 1 liter of FeCl₃, and 55 grams of iron plated off on the electrode, you store about 90ish watt-hours.\n\nSo 1.5 cubic meters of FeCl₂ turning into 1 cubic meter of FeCl₃, and 55 kg of iron plated off on the electrode, you store about 90ish kilowatt-hours of electricity.\n\nUnfortunately, FeCl₃ is also a fairly nasty thing which needs to be in highly acidic conditions - and not exposed to oxygen or it will begin converting itself into FeOH gunk. It is not quite as bad as pure HCl but it's still an acid.",
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