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Most efficient way to Electrolisize water into H2 and O2


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What is the most efficient way to create Hydrogen and Oxygen gas from the electrolysis of water?

 

I have done much research on the internet in this area, though what scare information i found of any value came from basic science experiments done by elementary school children. This distressed me much, as I wish to try and find an effeicent way to electrolysize water into hydrogen and oxygen for an experiment I am conducting.

 

My reasearch and limited knowlege on the subject has turned up several facts, the authenticity of which i cannot be 100% sure of.

1) Use of NaCl (table salt), Baking soda, or Sulfuric acid in an aqueous solution will increase production of either hydrogen or oxygen at the expense of one or the other.

2) Hydrogen forms at the negative electrode, and Oxygen at the positive electrode.

3) only 1.23 to 1.75 volts are needed for electrolysis, and increasing voltage/current with more wattage will increase production at the expense of efficiency.

4) platinum is a good material for a cathode or anode, though i do not understand why copper or stainless steel nails/wire would not...

 

Points two and three are rather easy to understand and impliment in an electrolysis device. I plan to use rather "crude" parts as I cannot afford much more expensive parts that would give more finesse to the finished product.

 

For point two i plan on using several PVC pipes within a much larger pipe, each smaller PVC with it's own cathode or anode. This will create oxygen producing and hydrogen producing pipes respectivly. The larger pipe would simply enclose the general structure so all pipes may be submerged in water at the same time and can share the same resivoir more easily.

 

Point three is where i get a bit creative. By using a PC power supply, i can create a uniform 12v current throughout the aparatus, attaching negative and positive wires equally for the variosu hydrogen and oxygen producint tubes. I am thinking a 2:1 ratio of H2 to O2 tubes to be more uniform with the relative 2:1 ratios of the gases present in water. As for what material to use for the cathods/anodes...well, i beleive that a copper net would be most appropriate as it would increase surface area greaty, and copper is cheaper than platinum.

 

The first point however is where the facts seem to break down... is it better to use baking soda or salt as a conductive ion/anion in the sollution? or perhaps a mixture of both? would placing just baking soda or salt separatly within hydrogen/oxygen tubes increase production of the gas they are supposed to help create? (I do not know which salt produces which gas more efficiently as i have varying and conflicting sources) Clarification in this area would expediate the design of the device greatly.

 

Please clarify me where I am wrong, and if possible provide some useful websites or books i can read at my local library. The faster i get clarification, the faster i can design a prototype. The picture of which will be posted here of course, soon thereafter i will be creating the real thing and testing it. and yes, i will be igniting the mixture. My plan is to create a device large/efficient enough to be both light and create hydrogen/oxygen quickly enough to burn a solid flame without having to store up the gasses.

 

I mean a large 4-5 inch flame, not just a ciggareete lighter flame. If all goes according to plan, i will have a completed device built and ready within...say...a week. dependant on the rate of clarification of course.

 

In the distant future, such a device will work alongside identical devices to create large ammounts of hydrogen and oxygen to be stored in high capacity tanks. (though i will save that for another day.)

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get a small bucket and dip graphite (pencil led) electrodes attahed to the wires in the solution. Use NaCl, for u will need less of it to get the same eefect as Baking soda, but it will generate chlorine, but very little. U cannot use copper or iron or zinc for the will oxidize and react with the salt or get oxidized forming rust fort iron for example. THis will result in a ton of "crap" floating in you water and the electrodes will slowly dissolve. IT is horribly disgusting. Graphite, is neutral, and will not react so ur water will stay clear. however copper will not react to much but still will.

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Don't use NaCl. You will get a bunch of chlorine since in order to make the electrolysis even remotely efficient, you need a good deal of NaCl. Sodium bicarbonate is just as effective. Don't let anyone tell you otherwise. The same amount of ions are produced so there is no difference there.

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Thank you all for the info.

 

I take it that it's untrue the NaCl and Sodium Bicarbonate form one produce (oxygen/hydrogen) more efficiently than the other. EG: Baking soda forms more oxygen faster, and NaCl form more Hydrogen.

 

Then it's settled, i shall dissolve baking soda into the water instead. though i have some questions about this substance:

1) does it break down in any way in water like NaCl does?

2) will it leave the sollution or become useless after some time?

3) how much should i add into the water per liter for optimal results?

4) will it settle to the bottom after a while if the water cools? do i have to heat the water to keep it in an ideal sollution or is room temerature okay? will stirring be necessary?

 

Also, thanks for the advice in regards to the cathode/anode materials. Graphite seems rather inefficient though...i would prefer something i can form into a fine mesh for more surface area and greater effect. Unless I can find some really cheap fine platinum wire, i guess i will have to go with copper for the time being. I know it will oxidize slowly, but it's better than iron for sure. What about stainless steel? I know that is not supposed to rust, is it?

 

Here is the design I have thusly come up with:

hydrogen project.GIF

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Probably the BEST salt you could use would be sodium fluoride. NaF is very soluble in water, and the standard oxidation potential of water is -1.23 volts while that of the fluoride ion is about -2.87 volts. As a result, water is MUCH easier to oxidize than the fluoride ion is. This means that you won't get any contamination at the anode or cathode, and you'll be left with relatively pure hydrogen and oxygen. The chloride ion has a SOP of -1.36 which means that it should be more difficult to oxidize than water, but because the values are so close and because of various other things going on, the chloride ion is easily oxidized to chlorine gas. This also leads to the formation of various other compounds and generally makes a big mess. So by using good electrodes and a sodium fluoride electrolyte, you should be able to have a successful electrolysis.

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I think i might be putting alot more voltage into this than just 1.25 i am afraid.

 

using a PC power supply, I have mainly 12 volt connectors, though some also have 3 volt lines as well.

 

If i divide up a single line 10 ways however, would that in turn divide up the voltage evenly? that way 1.2 volts would be served to each line, and i would not exceed the decomposition voltage of NaF?

 

also, where would i procure large quantities of NaF? I am talking gallons here...

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Heh. You need quite a bit more volts than 1.25. I was just giving that example to show that the fluoride ion will not be oxidized into fluorine so your overall electrolysis will be nice and clean. Fluoride ions cannot be oxidized in an aqueous solution. That is why I suggested using them.

 

For the electrolysis, it's best to just have one anode and one cathode. Splitting everything up into multiple anodes/cathodes will just reduce the power each electrode is receiving and will probably slow down the reaction.

 

NaF is a solid crystal akin to NaCl (Table salt). It's just that NaCl can be oxidized to chlorine in an aqueous solution while NaF cannot be oxidized in an aqueous solution. Naf is pretty danged cheap, but the only place I can think of to get the stuff is a chemical supply house.

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Well you didnt say that!

 

I can supply a solid 12 volts to every cathode/anode, more if it would help. I have a nearly unlimited supply of old PC power supplies i can get from my computer class. They are only about 250-300 watts each though, so one per device will hopefully be enough.

 

Hopefully it's nice and conductive...but not toooo conductive. i don't want to blow a fuse or something.

 

so, looks like the salt is definatly going to be NaF, and the cathodes/anodes will be made of copper(though i would have liked to get platinum).

 

but what is the optimal voltage? 12v good? or should it be more...

also, what is the expected rate of electrolysis? would one such container containing 10 oxygen and hydrogen producing tubes be able to produce a solid uninterupted flame on it;s own?

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To maximize the electrolysis of water, you need lots of current. These means nice large electrodes with lots of surface area (looks like you're already going that way) and a hefty low voltage, high current supply. I know some guys who rewind microwave oven transformers for just such use. Link .

 

Of course you'd have to rectify the output (so you get hydrogen at one lead and oxyegen at the other) and that may be troublesome due to the high current (100+ amp diodes are hard to come by).

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what would a PC power supply do for me? I imagine it's somewhat low voltage (12v), and the current couldn't be that bad...right?

 

I know that it will work, but I need high capacity high production units here. I eventually planning on having 15-20 such units producing hydrogen for another experiment of mine.

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Older PC power supplies tend to be completely foolproof. They switch itself off if short circuit is detected and after removing 220V for some time they are ready for work again. So its good choice.

 

You cant use as much current as you my want because most of electrical energy will go for heating and you will end up with boiler instead of electrolyser. There is much less heating if you can get required currents using small voltages. Industrial electrolysers use most often 4...5V.

 

Best electrolyte for making H2 and O2 is NaOH solution. It conducts very well and you can use stainless steel as electrodes. No dissolving of electrdes and no byproducts are formed.

 

If you want just H2 its easyer to make it chemically by puting some Al foil to NaOH solution.

 

You have to be very cautious though. If your hydrogen gets contaminated with remarkable quantities of oxygen you have got explosive thats very unstable and any microscopic arc somewhere in your electrolyser will detonate it immediately.

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i cannot form graphite into a net/grid pattern, and hence i will have much less surface area and alot less production capabiliby.

 

Sure you can. Use the graphite rods from pencils. If you want to get a LOT of surface area (but it'll be fragile) make the grid out of .7 or .5 mm pencil "lead" for mechanical pencils. As for connecting them, implement some creativity. Soldering works, if you are patient (although, again, corrosion is an issue with the solder), but there's any number of other ways to do it. You don't even really need to solder, as long as the rods are connected.

 

And no, graphite (carbon) will NOT deteriorate. I've done a fair amount of electrolysizing with carbon (graphite) electrodes - I carved them out of a pencil - and they have never deteriorated on me. Then again, I've never used anything other than tap water for the water - nothing added - but that shouldn't make too much of a difference for the electrodes, because as has been said, carbon is inert.

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Sure you can. Use the graphite rods from pencils. If you want to get a LOT of surface area (but it'll be fragile) make the grid out of .7 or .5 mm pencil "lead" for mechanical pencils. As for connecting them' date=' implement some creativity.

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Thats a bad idea in this case. The 'lead' also contains lots of clay. If you really want to use graphite you can take apart lantern batteries and get the thick carbon rods out. I have had both types of rods react in electrolysis but I always use an electrolyte.

 

You could also try getting some cheap platinum wire from ebay and making a grid.

 

edit: this stuff looks nice to experiment with: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=3179&item=7512009373&rd=1&ssPageName=WDVW

The seller obviously doesn't know what hes talking about but with that price you cant go wrong. Even if it is platinum plated it doesn't really matter.

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Now about the PC power supplies...what should i look for? what statistics should it display on the side that would be in my favor to get high current and 4-5v voltage? (i am not completely familiar with the statistics display on the sides of the power supplies)

 

As for the electrodes, i plan on using copper for now, platinum when i become more comfortable with the device and decide it's time for an upgrade.

 

NaOH or NaF???

I'll let you two chem experts duke it out on this one. I think NaOH (liquid right?) would dissolve better in water...though NaF does seem to be good too.

Any explicit reasons why I should take one over the other?

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First decide what voltage you want to use (I would go with 12). Then just pick the supply with the highest current rating for that voltage. Most of them will have a box printed on the label that shows all the different voltages with the supplied currents for each.

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what is the current measured in? or does it just say current and then supply a number...

 

I really need to know details here, I will be grabbing four or five of these things over the next few days.

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