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Author Topic: Splitting Water, Can Graphene make this more efficient?  (Read 4998 times)

Offline Airthumbs

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 I mixed salt into tap water and used the cables for a jump starter as the anode and cathode in the solution.  I noticed by increasing the surface area of the one giving off all the hydrogen bubbles that it produced a larger quantity of the gas.  I collected the gas by filling a test tube with water and used a submerged funnel to catch all the gas given off. One of the terminals has a green substance begin to stick to the metal and I assume that was chloride. I collected enough hydrogen to fill a small 300ml bag in five minutes.  The reaction for gas emission was only around the terminal.

Now if I used Graphene as the material and made that multi-layered I could increase the surface area by an order of magnitude, would that increase the amount of hydrogen gas given off?  I also understand that Graphene is the most conductive substance currently available so I imagine that might help in the process?

Any ideas?



 

Offline evan_au

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #1 on: 27/01/2013 07:01:34 »
Graphene could certainly give you a larger surface area in contact with the water, as could carbon nanotubes (rolled-up graphene) or sintered metal electrodes.

The problem with graphene is that its extremely high conductivity occurs in the plane of the graphene, not from the graphene to the water, so most of this area is not effective as an electrode - only at the edges of the graphene sheets. Oxygen and hydrogen ions concentrating at the edges of the sheet are likely to react with the unpaired bonds of the carbon atoms.

But conductivity in the electrodes is not a real problem, since the main resistance is in the water - so metal electrodes should work fairly well (as well as being cheaper than current sources of graphene).

Chemically, I am suspicious that the gas was coming from only one electrode. If the experiment were breaking down water, you would expect oxygen at the positive electrode, and twice the volume of hydrogen at the negative electrode. If it were breaking down salt (NaCl), you would get Chlorine at the positive electrode (which is very reactive, so it might react with the electrode material), and sodium at the negative electrode (which is very reactive, so it will react with water to release hydrogen).

Can you confirm that the jumper cables were made of copper? In this case, you could get green/blue copper chloride on the positive terminal. Note that Copper Chloride is not a good conductor, so the electrode contact with the water will degrade over time.
 

Offline CliffordK

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #2 on: 27/01/2013 07:30:32 »
I have a welder that makes and burns mixed gas, 2H2 + O2.  By mixing the gasses, it can have the electrodes in rings, spaced a short distance apart.  Don't you get bubbles forming on the electrodes?  One would certainly have to  have a system rigid enough that the positive and negative electrodes would not touch.

Otherwise, I believe that you need some kind of ion exchange.  So, having too large of electrodes with keeping the H2 & O2 in separate chambers may hinder the ion exchange, and not provide a significant benefit.
 

Offline Airthumbs

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #3 on: 27/01/2013 14:26:09 »
I was expecting gas from both terminals also and was very surprised when none came from the positive terminal.  All that formed was the blue/green material, which came off easily.  I studied the wire closely to see if there was even any sign of smaller bubbles forming anywhere but there was nothing.

Once the gas had been collected from the negative terminal I ignited it and it certainly went up fast with that orange/red colour of Hydrogen.

The wires I used did appear to be copper. They were copper in colour anyway.  I know that if you use different metals as either the anode or cathode and a different solution you can get the result of Oxygen from one and Hydrogen from the other. That is what I was hoping for but I cannot find any information on the Internet.

 

Offline CliffordK

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #4 on: 28/01/2013 11:13:53 »
What "salt" did you use?

KOH/NaOH,

Or NaCl?

You likely will get better O2 production using the KOH or NaOH.
 

Offline Airthumbs

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #5 on: 29/01/2013 00:20:56 »
I'm not sure of the salt I used.... It's gone! 

 

Offline CliffordK

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #6 on: 29/01/2013 01:04:08 »
If you use "table salt", NaCl (or NoSalt (KCl)),  then you will have a side reaction with Cl2 being formed at one of the electrodes.  The chlorine would be highly reactive, and you may be finding that it is reacting with your electrodes rather than bubbling out of solution.  Do you also get the formation of some water soluble sodium hypochlorite (NaClO), which is also reactive?

If you use NaOH or KOH (Lye or potash), often found in some types of drain cleaner, then you will not form the chlorine products.  The sodium or potassium will remain in solution, and you should get the formation of more oxygen.
 

Offline chiralSPO

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #7 on: 17/05/2015 01:29:39 »
Welcome back Airthumbs!

I looked up some of your older posts and saw this one, so I figured I'd add my two cents:

Unfortunately copper is easier to oxidize that water is, so you won't end up making much oxygen using a copper electrode on the positive end (anode). The copper will corrode instead (forming lovely blue and/or green copper salts) and eventually either covering or dissolving the entire electrode, severely limiting the utility of the whole electrolytic cell.

I recommend stainless steel (304 or 316 grades work quite well) or nickel metal for the anode. Copper works just fine for the hydrogen side (cathode).

Also, as CliffordK has pointed out, "table salt" is not the best choice--it will increase the rate of corrosion at the anode (unless you're using platinum or iridium etc.) Sodium or potassium hydroxide would be ideal. The solutions do not need to be very concentrated, a few grams per liter is sufficient, but the more concentrated it is, the better the reaction will work (be careful though, even dilute solutions of sodium or potassium hydroxide are caustic, and can burn you; and if you decide to make a fairly concentrated solution, it will get quite hot as the solids dissolve!)
« Last Edit: 17/05/2015 01:33:10 by chiralSPO »
 

Offline evan_au

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #8 on: 17/05/2015 20:49:00 »
Quote from: Airthumbs
if I used Graphene as the material and made that multi-layered I could increase the surface area by an order of magnitude
Improving the surface area of the electrodes is a good idea.

Unfortunately, multi-layer graphene (with say, 100 layers) has almost exactly the same surface area as a single sheet of graphene. To increase the surface area, it would be better to use 100 single sheets of graphene, or another form of carbon with a higher ratio of surface area to mass, such as carbon nanotubes.
 

Offline jccc

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #9 on: 17/05/2015 21:05:38 »
try gold plated wires/meshes for electrodes, add vinegar in water.
 

Offline Airthumbs

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #10 on: 27/05/2015 00:24:34 »
I am pretty sure that one of you people responding to this post certainly knows the most effective way of splitting water.  Instead of me messing around with various different forms of salt I should be splitting water without having to add chemicals to the liquid?

I like the idea of using a gold coated mesh as that would seem to infer that I might get a cleaner reaction over a larger surface area. 

What I find interesting is the suggestion I should add vinegar.  They split water on the International Space Station, and they must do this in the most efficient way possible, and that is?

Is this a dead donkey or what? 

Still I would like to know what the most efficient way to split water is and then once I have that information I can rest peacefully.

I just scanned the internet and still find that the simple instructions on how to split water are absent still.  No guide on current, liquid, or what the best anode and cathodes are. Nothing, not a jot of information on something so simple.  No information on using solar panels to provide the current, nada!

The total absence of this information is a little disturbing don't you think?

It is almost as if this information is being subverted, can you believe it at a time when hydrogen fuel cells are becoming more common!

So come on the Naked Scientists, what is the recipe?
« Last Edit: 27/05/2015 00:38:14 by Airthumbs »
 

Offline chiralSPO

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #11 on: 27/05/2015 03:27:27 »
I am pretty sure that one of you people responding to this post certainly knows the most effective way of splitting water.

I'll give it a try, though "most effective" depends on how you want to judge effectiveness (most cost effective, most efficient, most sustainable, most hydrogen per second, purest hydrogen, etc. etc.)

I just scanned the internet and still find that the simple instructions on how to split water are absent still.  No guide on current, liquid, or what the best anode and cathodes are. Nothing, not a jot of information on something so simple.  No information on using solar panels to provide the current, nada!

The total absence of this information is a little disturbing don't you think?

It is almost as if this information is being subverted, can you believe it at a time when hydrogen fuel cells are becoming more common!

I don't think there is anything subversive going on here, you may just be looking for information in the wrong places.

Here are a few links to get you on the right path:
http://en.wikipedia.org/wiki/Electrolysis_of_water
http://energy.gov/eere/fuelcells/hydrogen-production-electrolysis
http://www.cres.gr/kape/publications/papers/dimosieyseis/ydrogen/A%20REVIEW%20ON%20WATER%20ELECTROLYSIS.pdf
http://www1.lsbu.ac.uk/water/electrolysis.html

And here are some DIY instructions on how to build an electrolyzer (not necessarily that efficient, but much better than gold mesh in pure water)
http://www.instructables.com/id/How-to-Convert-Water-into-Fuel-by-Building-a-DIY-O/

Instead of me messing around with various different forms of salt I should be splitting water without having to add chemicals to the liquid?

While it is possible to split pure water electrolytically, this is very inefficient. Pure water is an extremely poor conductor of electricity (>18 MΩ*cm). Adding ions to the solution can substantially increase the conductivity, thereby increasing the efficiency. Also, depending on what type of materials the electrodes are made of (and if there is an ion-conducting membrane involved) adjusting the pH to very high or very low often increases the performance of the electrolysis.

I like the idea of using a gold coated mesh as that would seem to infer that I might get a cleaner reaction over a larger surface area. 

Mesh is a good idea (more surface area is good), but gold is not the best material despite being very corrosion resistant. Platinum mesh would work much, much better (as both anode and cathode). Nickel will also work quite well under alkaline conditions.

They split water on the International Space Station, and they must do this in the most efficient way possible, and that is?

They use a PEM (proton exchange membrane) electrolyzer on the ISS. It uses lots of high surface area platinum (and maybe iridium too) and operates at a pH of 0.
 

Offline Airthumbs

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #12 on: 27/05/2015 05:28:55 »
Excellent, thank you very much for the reply in the post above.  I shall study the links you provided in detail and get back to you with some more questions most likely.....  :o
 

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Re: Splitting Water, Can Graphene make this more efficient?
« Reply #12 on: 27/05/2015 05:28:55 »

 

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