Electrolysis at high vs. low voltages

[brads3290]

Recently I've been trying out some electrolysis, just to observe the results (and catch the occasional bit of hydrogen ), and I'm hoping to start learning much more about chemistry in general, as at the moment I don't really know much about this. When I decided to first do the experiment, the only power source I had access to (that didn't provide a deadly current, that is) was an old 30v 333mA charger, on which I did some chopping and extracted the two terminals.

 

I've been using this for the past couple of days to try different things, and I've read a couple of threads on here and I noticed mention that 12v is too high to get good results on some processes... Well I guess I'm out of luck there!

 

This was on http://www.scienceforums.net/topic/14412-more-copper-electrolysis-fun/- post #4:

 

 

I was using 12V (I know its too much but its all I've got atm).

 

Would anyone please be able to explain the differences, both in the way the reaction happens and the results achieved, between high voltages (say, 12v, even 30v ), and the lower voltages (say, 4-5v?). Also, does the current drawn make a huge difference? As mentioned before, the power supply I'm using limits the current to 333mA.

 

Thanks in advance, and please do let me know if the 30v 333mA PS particularly unsafe.. I'd rather be told I'm naive than figure it out the hard way! (though it does seem as though the current is too weak to penetrate skin - I've only felt a shock, and a tiny one at that, if water transfers current into a wound on my finger)

Edited December 10, 2015 by brads3290

[Sensei]

When I decided to first do the experiment, the only power source I had access to was an old 30v 333mA charger, on which I did some chopping and extracted the two terminals.

333 mA is just maximum after exceeding it for too long time power supply will be damaged.

What is the real current flowing through circuit, you should measure using the real ampere meter, plugged serial to your circuit, while it's running.

 

Power supplies which can have many amperes cost plentiful of money.

The cheapest thing you can do is using 230 V, 1-3 A rectifying diodes, 4 pieces, and make rectifying bridge.

1 A, 400 V max, rectifying diode cost $0.025 (yes, 2.5 cents), the last time I bought them.

Even this smoothing capacitor is not needed. As electrolysis happens without it anyway.

 

Transformer from 230 V -> 24V 5A, costs here $25 (250 times more expensive than above high voltage solution).

 

Producing 25 mL of Hydrogen using 230 V takes 90 seconds, with Gold and tap water with salt addition.

Producing 100 mL of Hydrogen using 230 V takes 90 minutes, with Gold and tap water without salt addition (less than 0.07 kWh energy used)

 

The larger current, the more molecules are separated, and more Hydrogen produced. Whether there will be Oxygen on positive electrode, depends on what metal is used for it. I recommend Gold. 24 carat Gold, so rings 14 carats and 18 carats are not good enough and would be damaged permanently, as whatever 2nd alloy metal they have like Silver or Copper will dissolve.

 

Water will be heated during electrolysis with such voltage.

The worst est is electrolysis of water with Iron electrodes.

Water temperature can reach 100 C. And current goes to 3 A (700 Watts).

In this particular case, you need to watch it all the time. It won't be long maybe 20 minutes

Edited December 11, 2015 by Sensei

[studiot]

Here is my Rough Guide to Electrolysis.

 

Both safety and voltage depend upon what you want to electrolyse.

 

Basically the higher the voltage the faster the electrolysis process so 30v may produce some rather rapid fizzing with some solutions.

 

For experimental purposes some way of varying the voltage is highly desirable.

 

Electrolysis works like this

 

 

Above some threshold (which may be close to zero) the greater the voltage the greater the current and the faster the elctrolysis proceeds.

This can be seen in the two curves shown in the sketch.

The threshold voltage is called the experimental decomposition voltage and is about 1.7 volts for sulphuric acid.

 

Some solutions release noxious or explosive gases on electrolysis, some are hazardous in themselves.

For instance the electrolysis of copper sulphate is OK with copper electrodes but the sulphuric acid requires platinum electrodes or they will be eaten away.

Edited December 10, 2015 by studiot

[brads3290]

Thanks for the great advice guys! In future I might have access to different solutions, but at the moment I'm just limited to adding different household things to tap water to create the solution. I've done it with salt (if the salt is dissolved properly, the water ends up cloudy blue, if it isn't dissolved, the water goes yellow when it's disturbed - Chlorine?).

 

Could I make much Hydrogen if I used salt with copper electrodes? I don't really have access to gold at the moment. Also I don't have a way of measuring the current drawn (I'm yet to buy any proper equipment), though my power supply does cut out when I short the circuit (including adding too much salt, making the water too conductive), could that be a protective mechanism to prevent damage?

 

The only other thing is that I'm pretty hesitant to use current that reaches dangerous level, as I've not had any formal training in this stuff, and I'd really rather wait till I'm more experienced to risk playing with anything that could give more than a mild shock.

 

In the future I hope to figure out how I can access other chemicals, such as Sulfuric Acid and Copper Sulfate. Are there any substances other than salt that would work nicely? I've heard that Bi-Carb Soda works nicely, as does Vinegar and Sodium Acetate (the other product of the soda-vinegar reaction, right?).

[Sensei]

Sodium bicarbonate + Acetic acid -> Sodium acetate + Carbon dioxide (gaseous) and water.

 

Sodium bicarbonate is used to bake cakes (2nd name for it is baking soda). So it's available in any food supermarket.

I am using it to bake pumpkin cake.

 

Yes, they works, because they're ions while dissolved in water.

But you will have plentiful of other reactions going on, if you won't use inert metal like Gold.

f.e. Acetic acid + Copper Oxide/Hydroxide -> Copper acetate + water.

You see by yourself, bluish color is probably Copper wire dissolved in water.

Edited December 11, 2015 by Sensei

[John Cuthber]

Since he didn't make it clear: I will just point out that without an isolating and voltage reducing transformer, the circuit that Sensei drew is probably lethal.

 

Also, in general, raising the voltage just makes the system less efficient- you waste more heat.

[studiot]

I agree with John Cutheber, that you need to be confident in electronics before you start making your own mains driven stuff.

 

You 30 volt supply is safe but unwieldy.

 

Here is a robust cheap module that will add on to it to make a variable supply that includes a voltmeter and is short circuit proof.

 

There are many available at around £6 including postage the link is an example supply.

 

http://www.ebay.co.uk/itm/LM317-Adjustable-Voltage-Regulator-Step-down-Power-Supply-Module-W-LED-5KR8/181887572382?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D33196%26meid%3D499427c93d3b44eea3a096e73829d5c1%26pid%3D100005%26rk%3D4%26rkt%3D6%26sd%3D331280958905#ht_9870wt_1059

[John Cuthber]

Let's be absolutely clear about this.

Using high voltage (more than about 4 or 5 volts) is the wrong way to go.

 

 

The commercial systems use a handful of volts and 150000 amps

https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_process

[brads3290]

Hmm.. That's interesting. So how does having a low voltage and really high current make it better for electrolysis? Does it depend on what you're trying to achieve, or is this just the generally accepted way to go?

[Sensei]

Hmm.. That's interesting. So how does having a low voltage and really high current make it better for electrolysis? Does it depend on what you're trying to achieve, or is this just the generally accepted way to go?

You have to look what real means high current.

 

Current, in amperes, multiplied by time is Charge:

 

Q=I*t

 

in Coulombs.

 

1 electron has charge equal to 1.602176565*10^-19 C.

 

so if you divide Q/e you have quantity of electrons.

 

In the case of Gold, or inert metal electrolysis, where is made Oxygen there are needed 4 electrons to separate 4 molecules of water:

 

4e^- + 4H₂O -> 4 OH^- + 2 H₂

and produces Hydrogen gas, which is appearing on negative electrode.

 

OH^- goes through water to positive electrode:

4 OH^- -> 2H₂O + O₂ + 4e^-

Oxygen gas (half as much as Hydrogen gas) is appearing on positive electrode.

(electrons taken by positive electrode)

 

The larger current, the larger charge, the larger quantity of electrons and the more volume of gas produced.

 

If your watt meter is counting current, or ampere meter, you can even predict amount (volume) of produced gas and how long you have to wait for it.

 

High voltage (230 V) and low current (like 2 A), means that water is heated. Energy is spend on heating water, instead of splitting water molecules.

P=I*U=230 V * 2A = 460 W

E=Q*U=230 V * 1s * 2A = 460 J

But with small voltage and large current:

P=I*U=5V * 92 A = 460 W

E=Q*U=5V * 1s * 92A = 460 J

Same power, same energy, but different quantity of electrons, and different volume of gas produced.

Energy does not disappear. It's wasted on heating water in the first case.

But it's hard (expensive) to make really high current at home.

Edited December 16, 2015 by Sensei