# Electrolysis of water...

## Recommended Posts

I remember reading about electrolysis of water before learning about it in chemistry class during the school year, and now I want to try it. First off, what is a safe electrolyte for it? Also, since the quantity of products is determined by the charge transferred, (as in the current and low long the current is flowing) then what effect other than determining whether or not electrolysis occurs does the voltage have? As in, if the charge transferred is the same in one case where the voltage is barely above the cell potential and another case where the voltage is much higher than the cell potential, since the energy transferred will be much higher, where does that extra energy go? Would it heat the solution?

If I were to do water electrolysis using a 1.5 volt cell (I think water's cell potential is 1.23 volts) would the extra 0.27 volts not dissipated by the electrolysis overheat the cell? Also, would the size of the water container affect it?

##### Share on other sites

the cell will not over heat from an additional 0.27 volts. the 0.27 volts will go towards increasing the amperage. the size of the cell can have an effect on the rate of the production, for example two big plate electrodes will provide a higher rate as the resistance will be less and more current can flow compared to two wire electrodes.

you don't technically need an electrolyte for this but if you must then use a bit of sodium hydroxide. this will not give off any gasses like sodium chloride would.

and yes, there is heat generated because of resistance withing the cell as if it was part of a normal electric circuit. i suggest you read some stuff about basic electronics. it can be useful.

##### Share on other sites

the cell will not over heat from an additional 0.27 volts. the 0.27 volts will go towards increasing the amperage. the size of the cell can have an effect on the rate of the production, for example two big plate electrodes will provide a higher rate as the resistance will be less and more current can flow compared to two wire electrodes.

you don't technically need an electrolyte for this but if you must then use a bit of sodium hydroxide. this will not give off any gasses like sodium chloride would.

and yes, there is heat generated because of resistance withing the cell as if it was part of a normal electric circuit. i suggest you read some stuff about basic electronics. it can be useful.

Actually I'm basing this on a combination of what I remember from the electricity and magnetism unit from physics class and the electrochemistry unit from chemistry class. I thought that the voltage drop from the load (water) had to be as much as the voltage increase from the power supply?

Also I don't know where to get sodium hydroxide but would sodium hydrogen carbonate do the trick? I thought I remember reading that an electrolyte was necessary.

Also, what effect would the distance between the electrodes in the water have? If the electrodes were placed further apart would that simply mean there would be more resistance and therefore less current would flow despite the same voltage drop?

Oh and graphite is a conductor, right? So if I used graphite rods (I know how to isolate the graphite from a pencil; burn the pencil and the wood peels off leaving the graphite intact) as electrodes would that work?

##### Share on other sites

The need for an electrolyte depends on the purity of the water. Tap water probably doesn't need much, if any. Distilled water will need something to be added.

From a practical standpoint, you should use more than 1.5V. You need to disassociate the water, but there are also other issues. There's a bias at the electrodes that needs to be overcome as well, and also what happens when the gas forms on the electrode — you need it to bubble off, and want a faster reaction, so you'll get better results with a higher V.

Actually I'm basing this on a combination of what I remember from the electricity and magnetism unit from physics class and the electrochemistry unit from chemistry class. I thought that the voltage drop from the load (water) had to be as much as the voltage increase from the power supply?

Both are right.

V = IR

You get a drop of V over the whole path; a higher I means that you get a larger drop in V.

Also, what effect would the distance between the electrodes in the water have? If the electrodes were placed further apart would that simply mean there would be more resistance and therefore less current would flow despite the same voltage drop?

Right.

##### Share on other sites

Trying to do this without an electrolyte will probably give rather disapointing results. While there are impurties in tap water that will make it a better conductor than pure water (which, btw, does conduct but rather badly) there are not many.

Bicarbonate of soda would work well but it isn't very soluble.

Turning it into the carbonate would improve the solubility.

Of course, you could just use washing soda too start with or you could heat the bicarbonate to decompose it.

If I didn't have any carbonate I would put a tablespoon full of bicarbonate in a teacup and add boiling water fairly slowly while stiring the stuff. The bicarbonate decomposes to carbonate and gives off CO2 (which is why ou add the water slowly).

The solution of carbonate (and some bicarbonate) will do as an electrolyte.

It would be interesting to compare this with just tap water using the same setup.

The remaining 0.27V or so will go into heating the stuff, but even if you get a few amps of current flowing ( which would be good going with a simple set up) you are only talking about a watt or so of power- nothing to worry about.

Pencil lead electodes work well enough. Welding carbons or the carbon rods from old zinc/ carbon cells work better. Of course, you can always ask father Christmas for some platinum.

##### Share on other sites

I got this to work really well once with tap water a nine volt battery and some wire when I was a kid. For electrodes I basically opened up a couple batteries carefully enough not to break anything.

##### Share on other sites

The remaining 0.27V or so will go into heating the stuff, but even if you get a few amps of current flowing ( which would be good going with a simple set up) you are only talking about a watt or so of power- nothing to worry about.

It's quite likely, though, that you need more than 0.27V of overvoltage to compensate for the non-ideal parts of the system, as I mentioned above. If one goes out on the web, there are descriptions of people doing this and needing 2.0V or 2.5V or more, depending on the electrode type.

##### Share on other sites

Swansont is right. The overpotential for formation of oxygen at the anode can be as high as 1 volt and for formation of hydrogen at the cathode it certainly is more than 0.5 volt. So, better to start with at least 3 volts, but a 4.5 volts cell would even be better.

##### Share on other sites

The need for an electrolyte depends on the purity of the water. Tap water probably doesn't need much, if any. Distilled water will need something to be added.

From a practical standpoint, you should use more than 1.5V. You need to disassociate the water, but there are also other issues. There's a bias at the electrodes that needs to be overcome as well, and also what happens when the gas forms on the electrode — you need it to bubble off, and want a faster reaction, so you'll get better results with a higher V.

Both are right.

V = IR

You get a drop of V over the whole path; a higher I means that you get a larger drop in V.

Well, yeah, I know about that, Ohm's Law, I remember that from grade 12 Physics class. I think the voltage drop is fixed as also being the voltage increase and therefore doesn't vary but the current drawn depends on the voltage and the resistance...

As for the overvoltage, ok I'm getting mixed messages about what voltage to use; so would using too high-voltage a source (since the voltage will drop as much as it raised no matter what the load) cause the voltage supply to overheat? If I did that with a battery would that cause the battery to leak?So if I used a power outlet, and put wires in an extension cord that connected to the graphite rods in the water? Is there a danger of something in the wall overheating or am I safe with a power outlet?

Also, how do you capture the hydrogen and oxygen separately? In my chemistry textbook on a page about electrolysis of aqueous potassium iodide there was some weird U-shaped water container and I'm guessing that's for capturing different gases at the top, but I was thinking if I wanted to fill one balloon with hydrogen and another with oxygen what kind of method would be practical to use?

And with regards to the electrolyte I don't know if I have sodium carbonate, what are some other good electrolytes? What about vinegar, is that a safe and efficient electroylte? (I know that vinegar is an acid and acids and bases are conductive) Graphite from a pencil lead won't react with vinegar right?

On the other hand sodium hydroxide would be efficient and wouldn't give off any gases other than hydrogen and oxygen, right? So where could I get sodium hydroxide? Does anyone here know a few different safe electrolytes (by safe I mean won't give off harmful gases) and where to get them?

##### Share on other sites

I'd stay far away from using power from an outlet. A 9V battery would be sufficient.

##### Share on other sites

at most, use 12V.

whats the mains voltage where you are 110VAC? not good for electrolysis. partly because the voltage is immense for the scale of what you are planning but mostly because AC will produce hydrogen and oxygen at both electrodes.

##### Share on other sites

"I got this to work really well once with tap water a nine volt battery and some wire when I was a kid. For electrodes I basically opened up a couple batteries carefully enough not to break anything"

OK so you got a current to flow by using about 7 times the voltage that you need. My idea of " work really well" doesn't include something that inefficient.

Think about it, if you only need about 1.2V and you end up using 12V then you are throwing away 90% of the energy. Is adding an electrolyte that difficult?

##### Share on other sites

I will point out also that a PEM cell, will electrolyse De-ionised water perfectly, in fact Tap water will kill the cell over time.

and 3 volts is Plenty.

##### Share on other sites

What does the "E" stand for in PEM?

##### Share on other sites

Ok got it, don't use a power outlet; so with regards to electrolytes, could someone name an efficient electrolyte that doesn't give off harmful gases AND where to get that electrolyte, and what voltage I'd be best using with that electrolyte? I remember I read before that sulfuric acid would make a good electrolyte but what happens to the sulfur? Does it give off sulfur oxides? If not, where could I get it? Or better yet, what I asked earlier about efficient electrolytes and where to get them...

##### Share on other sites

What does the "E" stand for in PEM?

Exchange.

##### Share on other sites

Sulphuric acid is a good electrolyte (if rather corrosive). The sulphate ion is very stable and the sulphur all stays in solution.

Also, as I answered earlier, washing soda works too.

With a good electrolyte like those and reasonable sized electrodes you should be able to see the bubbles of H2 and O2 with a 1.5V cell. A couple of cells should be plenty but, while it's less efficient, using more voltage won't do any harm.

Since you don't want AC and using the mains is dangerous anyway I wouldn't recommend it.

##### Share on other sites

Sulphuric acid is a good electrolyte (if rather corrosive). The sulphate ion is very stable and the sulphur all stays in solution.

Also, as I answered earlier, washing soda works too.

With a good electrolyte like those and reasonable sized electrodes you should be able to see the bubbles of H2 and O2 with a 1.5V cell. A couple of cells should be plenty but, while it's less efficient, using more voltage won't do any harm.

Since you don't want AC and using the mains is dangerous anyway I wouldn't recommend it.

Yeah I mentioned already how I got it not to use a power outlet.

Anyway, as for the washing soda, does it work almost as well as sulfuric acid? I know the latter is corrosive but I'd be careful with it; though then again it is better to lean on the safe side anyway. So where could I get it? Also, what about vinegar? How well would that work, and what gases would that give off?

Also, how do you capture the hydrogen and oxygen separately? In my chemistry textbook on a page about electrolysis of aqueous potassium iodide there was some weird U-shaped water container and I'm guessing that's for capturing different gases at the top, but I was thinking if I wanted to fill one balloon with hydrogen and another with oxygen what kind of method would be practical to use?

##### Share on other sites

A balloon won't work unless you have a way to compress the gases. A test tube or other rigid volume. If it's clear you can see how much you have collected.

##### Share on other sites

A balloon won't work unless you have a way to compress the gases. A test tube or other rigid volume. If it's clear you can see how much you have collected.

Test tube? What about a tall glass or empty plastic bottle, could either of them work similarly? Either way, how would you set them (or a test tube) up to collect the gases?

##### Share on other sites

get a bucket fill it with water, get a plastic soda bottle fill it with water.

put the bottle into the bucket with the screw top end pointing down.

put a pipe into that bottle.

connect the pipe to the Hydrogen generator and the gas will displace the water out of the bottle.

That`s how you "catch" it, also if you Hold the bottle under the water and let it fill with H2 gas, it will also be under pressure, if you had a tap for the top (the Real Base of the bottle) you could bleed the H2 gas off.

the best part is that being all plastic and water, any explosion will be reasonably Safe too, just Very wet and Loud.

## Create an account or sign in to comment

You need to be a member in order to leave a comment

## Create an account

Sign up for a new account in our community. It's easy!

Register a new account