I’ve done electrolysis experimaents before, the ones with beakers and batteries and electrodes stuck in pools of water. I understand all that, but how do the new (well not new, but you get it) solid electrolysis cells work? the ones that they use on nuclear submarines and things. also, any ideas on what the relationship between electricity input and gass out put is in a cell?
I haven’t the faintest clue of what you might be talking about but, while we wait for some serious input, I will proceed to relate a humorous anecdote.
I own a sailboat which, like all boats, needs to have sacrificial zinc anodes replaced regularly so the electrolysis will not eat away other useful things like the propeller or the prop shaft.
My friendly bartender is also a boat owner and we sometimes talk about boats. So one day I ask him if he knows anything about electrolysis and he says not really. I keep mentioning the subject and we both realize the conversation is getting to be very weird. Finally I say “What the hell are you talking about?” and he says “No, what the hell are you talking about”.
Well, it turned out “electrolysis” is the name of a hair removal system which his girlfriend had used and I did not have a clue anything like that existed by that name. And he, in spite of owning a boat, had never heard of corrosion caused by electrolysis. We had a good laugh when we realized the misunderstanding.
Now I see the title of this thread and I have about the same feeling that maybe I am missing something… so, rather than make a fool of myself, I’ll stand back and watch how this develops. If it turns out we are talking about bikini lines I will promptly offer my views on this interesting area.
I believe that castle_bravo is talking about nuclear submarines getting oxygen gas from sea water using electrolysis. I think that electrolysis is just a general term refering to any electrochemical reaction. I’m not sure what solid electrolysis cells are exactly, I need more information. I suspect they work in much the same way as the electrode beaker set-up you are familar with. The amount of electricty required is based on the standard reduction potential of the electrochemical. If I had my P-chem book with me I could tell you exactly what it is for the 2H2O to 2H2 and O2 reaction, but, alas, I do not.
Oh, we are not talking bikini lines then? What a disappointment!
Ok, if memory serves me right 96500 coulombs (= 26.8 AH) will deposit 1 mol on each electrode. you do the rest of the math.
This may be more than you want to know, but:
Electrolysis of water into hydrogen and oxygen:
H[sub]2[/sub]O is partially dissociated into H[sup]+[/sup] and OH[sup]-[/sup] ions.
At the anode, assuming an inert electrode such as platinum, the reaction is:
2H[sub]2[/sub]O ----> O[sub]2[/sub] + 4H[sup]+[/sup] + 4e
At the cathode, the reaction is:
4H[sup]+[/sup] + 4e ----> 2H[sub]2[/sub]
So for every four electrons which flow from the anode to the cathode, you get one molecule of O[sub]2[/sub] gas and two molecules of H[sub]2[/sub] gas. Or in more meaningful numbers, 96500 coulombs gives you 1/4 mole of oxygen gas (8 grams, or about 6 litres at room temperature and pressure) and 1/2 mole of hydrogen gas (1 gram, 12 litres).
As for the solid electrolyte, I’m not so familiar with this. Electrolysis can take place in any medium where ions are mobile, e.g. you can perform electrolysis in molten salt to generate chlorine gas and sodium metal. Ions are sufficiently mobile in some solids for electrolysis to take place - solid aluminium oxide has been used as an electrolyte in sodium-sulphur batteries, for example. Other ceramics can conduct potassium or sodium ions, and there is a polymer which conducts hydrogen ions. I don’t know how these are applied in nuclear submarines though.
>> 96500 coulombs gives you 1/4 mole of oxygen gas (8 grams, or about 6 litres at room temperature and pressure) and 1/2 mole of hydrogen gas (1 gram, 12 litres)
Are you absolutely, positively certain of this?
Thanks guys, that helps a lot. about the solid electrolysis cell, The actual name of the thing I was asking about is a solid polymer electrolyte electrolyxer. oh, and Dr. Lao was right when he said the subs used the SPE’s for obtaining oxygen sea water
Sailor:
**"96500 coulombs gives you 1/4 mole of oxygen gas (8 grams, or about 6 litres at room temperature and pressure) and 1/2 mole of hydrogen gas (1 gram, 12 litres)
Are you absolutely, positively certain of this?"**
Yep, pretty much! You have to take into account the number of electrons per atom in the electrochemical reaction, and the number of atoms in the end product.
96500 coulombs contains one mole of electrons. (Avogadro’s constant, 6.02x10[sup]23[/sup], multiplied by the charge on an electron in coulombs, 1.60x10[sup]-19[/sup].)
So if you have one electron per atom involved in the reaction, 96500 coulombs gives you one mole of atoms. This is true of hydrogen ions:
H[sup]+[/sup] + e ---->H
so you get one mole of hydrogen ATOMS, H.
These combine to give you half a mole of hydrogen gas MOLECULES, H[sub]2[/sub].
From the stochiometry of water, you can see that for half a mole of hydrogen you must also get 1/4 mole of oxygen.
Ok, I almost get what you mean by all of the mathematics, except I don’t know what a coulomb is. I looked it up, and it said that it was the amount of electricity flowing past a cross section of an electric circuit at one ampere. I’m not in any way an electrical engineer, so this just confused me. How much electricity does one coulomb represent?
One Coulomb is the amount of charge accumulated in one second by a current of one ampere. As simple as that.