383Views18Replies

# can anybody please give me all the info about electrolysis of water?like: how much voltage ? Answered

Tags:

The forums are retiring in 2021 and are now closed for new topics and comments.

For an overview, you can (and should) read the Wikipedia article the subject, here
http://en.wikipedia.org/wiki/Electrolysis_of_water

I think that Wiki article is a good introduction, but maybe a little short on practical hints, like what materials to use for the electrodes and the electrolyte, and what sort of voltage, and/or current, is needed to make the reaction happen.

Regarding voltage and current, the two most important principles to understand are:

(1)The reaction rate is proportional to the current. That is to say electrons are one of the reactants. If you can push electrons through your cell faster, you produce gasses faster.

(2)There is a minium voltage needed to make the reaction happen at all. I think it is somewhere around 2 volts. Putting more voltage across the cell will tend to increase the current, and thus make gasses faster, but at the expense of wasted power, which goes into heating the cell. I think a good compromise between gas production and wasted power is to try to run your cell at voltage between 4 and 6 volts.

Moving the electrodes closer together can improve efficiency, by making the paths for ion conduction shorter, and thus lowering resistance.
http://en.wikipedia.org/wiki/Electrical_resistance_and_conductance
However making the electrodes too close together, may cause problems in keeping the gasses from mixing with one another. Also if the electrodes are so close they can actually touch one another, then that's a short circuit, and you probably don't want that either.

If you get really serious about the power supply for your electrolytic cell, you may decide you want some sort of electronic regulation, e.g. constant current, or a firm upper limit on the cell voltage.  And here's one example of somebody who has engineered a power supply intended for the electrolysis of water.
http://www.powerstream.com/dc-hydrogen.htm
I'm not saying their box is actually worth its circa 200 USD sticker-price. I'm just saying they've at least thought about it a little bit,  and it is interesting to look at the solution they've come up with.

Regarding the electrodes and electrolyte, you want to choose materials that are unlikely to participate in chemical reactions that compete with the reactions you want to happen. For example if you chose NaCl (table salt) for the electrolyte, then Cl- ions may compete with OH- ions at the anode, giving you Cl2 gas in addition to, or instead of, O2 gas at the anode. A better choice would be Na2CO3 (washing soda) or NaHCO3 (baking soda).

You might be asking yourself, well why don't the CO3-2 ions try to come out of solution as CO2 gas at the anode? Or why don't the Na+ ions try to plate out as Na metal on the cathode?

And the answer to that question is essentially that certain chemicals, certain ions, like to stay dissolved in water. They really like the water. So much so, that just a few electron-volts is not enough energy to compel them to get out of the pool. For ions that are really water-soluble, like Na+, often the best way to get them out of solution is to put the whole swimming pool on a hot plate, and boil the water from under them.

Anyway, for the novice, it is really hard to guess at what kind of chemistry might happen for a given choice of materials, e.g. which ions are likely to stay in solution, which are likely to leave. For that reason it may be best to follow someone else's recipe, e.g. carbon electrodes, baking soda, and a 5 or 6-volt power supply.

thanks a lot!!!!
i m happy that finaly i have got what i wanted.

Can you give us all the info about what you actually want to know?

L

man, i had typed all my Q's, but somehow they didnt get published.
what i want 2 know is that , how much voltage & current is required for electrolysing 1kg of water; which electrode is best for this; which temperature is optimum for this reaction; what should be the minimum conc of additive salt(like NaCl,etc) ; can i use the graphite electrode from the ordinary battery cell(of 1.5V) & what would be the consequences; willl the temperature of water increase during the reaction & by what rate; what is the possible amount of leakage of water as vapour during the reaction (like .1 kg of water is wasted in the form of vapour/1 kg of initial water taken for experiment) ;is it possible to burn the H2 & O2 formed during the reaction & what would be the efficiency of the reaction?
so plz plz u ppl answer all my Q's bcoz i need 2 know this very urgently.
thank you for reading my Q & trying 2 think abt it !

You want to think in terms of energy.

1 Kg of water is 55.55 Mol.
The electrode potential is 1.23V

If I understand this correctly (http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html) you need 237.13 KJMol-1, which would be 13,174KJ.

How long it takes to electrolyse 1Kg affects the answer, and I think you'll have to go with what you can get out of your system.
E.g. 1A @ 1.5V is 1.5 watts, and you're only shifting 5.4KJ per hour at that. If you extrapolate to the full kilo, you're looking at 2440hours, or 100 days.
If you can cram 10A, you're down to 10 days at 15watts - and it'll be getting warm.

http://en.wikipedia.org/wiki/Electrolysis_of_water

But, you should end up with 2,666 litres of gas out of 1Kg water - what are you going to do with that?

L

actually i wanted 2 create some device which will convert water into H2 & O2; & then use this energy by combustion as & when required!
now the only thing i m having trouble with is that when H2 is created i need 2 store it under some pressure; & this will create back pressure, & efficiency of the system will decrease.
what i really wanted 2 know was that can i use just tap water ( having considerable hardness) without adding baking soda or any other stuff, so as 2 produce large amount of H2 gas, for combustion purpose.

As I remember, the Wikipedia article says something about electrolytes.
How are you going to store the gas? Maybe that should be the question?

L

to store i m using a tank.
to push the generated gases i m thinking of using a motor runing on wind energy!
so the back pressure wouldnt much affect the efficiency of the system.
thanks a lot 4 helping me so much......

Air-compressor?
You'll need a reservoir on the electrolytic-side and something like a pressure-switch. What's the plan?

L

sort of air compressor!
just so that the generated gases can be stored under pressure in a cylinder.
my plan is to electrolyse water & use hydrogen & oxygen for combustion (as & when required ) for hosehold purpose(like heating water for bathing, cooking,etc).
what' s ur opinion?
ya i know that its a bit dangerous , but i believe that if we control the combustion then we can use the gases successfully for our purpose.
what say?
:)

The only important question is "where are you getting the electricity from?
Pressurising gases costs money, you might find that buying cylinders is better if you want to run the household on pressurised gas.

L

You might want to also try PULSING the dc voltage. I have heard that if the DC voltage is PULSED at about 610 Hz... the electrolysis is much more intense. I have not tried it to verify this myself though.

water can be split into h2 and o2 from approximately 1.5v and the current depends on the total resistance the higher the voltage and current the quicker the gases are formed. you can use any conductive material for the electrodes, carbon is good because it is unaffected by the current passing though. I think a lower temperature is best because the resistance increases with heat. you should try and use baking soda instead of salt because salt releases chlorine which is poisonous while baking soda releases co2, the concentration while change the resistance allowing more current to flow - the more there is the greater the current will be. The temperature will increase depending on the amount of gas being produced. the two gases will explode if they are together to reform water although if you separate them the hydrogen will not burn unless exposed to oxygen.

i have posted all the details above , so plz try 2 answer it !
thank you>

Did you try doing any research of your own? Where did you look? What parts of the things you read did you not understand? Perhaps we can help clarify specific issues about which you are confused?

graphite electrodes. dc powersupply between 2-15v.water+salt or sodium bicarbonate(baking powder)

i have posted all the details below, plz try 2 answer them.
thank you.