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seperate tank electrolysis Answered

If I were to have 2 seperate buckets, one with ground and the other with something like 9 volts nothing would happen because the 2 bodies of water arn't connected. If I were to join the two bodies of water using a wire would electrolysis take place?

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Austringer (author)2007-12-11

I'm confused by something here......at T0 - when you start, what is in your two chambers?

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T3h_Muffinator (author)2007-12-09

It'll work, but I didn't expect your results If you want to do plating, I think you could try using a salt-bridge, but I'll have to look it up in my chem txtbook again. What'r you trying to do?

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user

I'm trying to design a fuel cell, and afer the test I'm going to use a metal plate to sperate the waters so that the gasses are seperated, which is required to get the electricity back out.

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user

Do you just need two tubes of each respective gas, or do you need two subcells, each that produces the compliment gas of the other?

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my goal is to make a AA size fuel cell. A divider will seperate the tube of the cell into 2/3 and 1/3, so that you get equal pressure for the oxygen and the hydrogen. Please don't steal my design, I promised Nacho that I'd make an instructable about it.

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jtobako (author)guyfrom7up2007-12-09

You need a permeable barrier, not a metal one. It MAY be as simple as something that keeps the O2 bubbles on one side and the H2 bubbles on the other, or it may need to be much more complicated : )

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guyfrom7up (author)jtobako2007-12-09

my aluminum barrier will work. When charging hydrogen bubbles will form around the negative platinum coils and oxygen bubbles will form on the right side of the alluminum barrier. When discharging the 2 platinum coils will do all of the work. I'm pretty sure this'll work, I did some experiments Another Pro with my design (took me abut 20 minutes to come up with a good solution) is that it'll work no matter what position it's in.

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jtobako (author)guyfrom7up2007-12-11

Could you explain something for me? How, physicaly, are the different parts of the water molecule going to get past the aluminum barrier? If 2 H2O become H2 and 2 -OH at one electrode, and 4 -OH become O2 and 2 H2O at the other. How do the other half of the water get past your aluminum barrier?

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Patrik (author)jtobako2007-12-09

Actually, what you need is called a proton exchange membrane.

In essence, you need something which is permeable to hydrogen atoms (or rather, H+ ions, aka protons), but not to H2 or O2 molecules.

PS: before you spend a lot of $$ on platinum to build this - you may want to take a few minutes to calculate how much energy you could store in an AA size fuel cell like this. You may also want to think about what happens when you turn a liquid into a gas in an enclosed space...

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guyfrom7up (author)Patrik2007-12-09

I'm pretty sure my design works, try it yourself if you are in doubt, I tried it and it works.

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Patrik (author)guyfrom7up2007-12-09

So - how much electricity do you get out of it?

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guyfrom7up (author)Patrik2007-12-10

havn't gotten that far, I still need to get some platinum

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Patrik (author)guyfrom7up2007-12-10

That's why I recommended calculating the storage capacity *before* you buy the platinum.

Let me just go ahead and do the calculation for you, if you don't mind:

- Energy released upon combustion of hydrogen:

2 H2(g) + O2(g) -> 2 H2O(l) + 572 kJ/mol

- Size of an AA battery: L 50.5 mm x D 13.5–14.5 mm

That comes out to a volume of about 2ml. Let's be generous and say that the internal volume available for hydrogen (2/3 of total internal volume) is 1 ml.

- Under standard conditions, one mole of gas is 22.4 liters

1 ml H2 is 0.01 liter, or 4.46 e-5 mole

The formula above uses 2 mole H2 to produce 572 kJ, so 4.46 e-5 mole H2 would produce 12.8 Joules of energy.

One Joule is equal to one Watt second. Typical output for a fuel cell is .7V, so on 12.8 Watt second you could get 18.2 A for one second (wow - sounds a lot, doesn't it?), or about 5 mAh (hm - doesn't sound as much anymore).

Now compare that to a standard NiCd rechargeable battery, which gets 650 to 800 mAh, and at a voltage which is twice as high.

To put that into perspective... you would need about 300 of you H2 fuel cell AA batteries to have a storage capacity equivalent to a single NiCd AA battery.

This illustrates one of the main problem with hydrogen fuel cell technology: stored as a gas, the energy density of hydrogen is very low compared to any liquid fuel.

Don't want to rain on your parade, and this does look like a great science project. But often it pays off to spend a few minutes figuring out on paper how well an idea would work...

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Patrik (author)Patrik2007-12-10

typo: 1 ml = 0.001 l = 4.46 e-5 mole ideal gas

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NachoMahma (author)2007-12-08

. If you're talking about plating, it won't work. That type of electrolysis involves the exchange of atoms.
. If you are talking about producing gases, I dunno. Talked to a EE, but he is trained in transmission/industrial electricity and he didn't know if it would work, either. I guess that it will work - let me know if I'm right or wrong.

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guyfrom7up (author)NachoMahma2007-12-08

well, I just did a test and here's my results: The cathode gathers hydrogen The anode gathers nothing the joining wire that's in the hydrogen gathers nothing The joining wire that's in the oxygen water gathers oxygen. I was not expecting that.

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Goodhart (author)guyfrom7up2007-12-09

that confirms what jtobako wrote then.

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NachoMahma (author)guyfrom7up2007-12-08

> The joining wire that's in the oxygen water gathers oxygen.
. I wasn't expecting that. And, if anything, I would have expected H2. Neat! I wonder why nothing on the other end?
. Thanks for the update.

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jtobako (author)2007-12-08

You would have 2 cells in series.

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