Introduction: Separate Hydrogen and Oxygen From Water Through Electrolysis

Picture of Separate Hydrogen and Oxygen From Water Through Electrolysis

Electrolysis a method of separating elements by pushing an electric current through a compound. It is used in various industrial applications such as removing copper from its ore. It is also used to separate hydrogen and oxygen from water. Electrolysis isn't the most efficient way to obtain hydrogen, but it is one of the easiest and cheapest ways to "homebrew" hydrogen.

Hydrogen is the most abundant element in the universe. With the "green-energy" craze and talk of powering our future oil-free economy on hydrogen, it has gotten much attention in the last few years. Learning about this potential fuel of the future is important and interesting. Besides, hydrogen is a powerful fuel, and blowing stuff up in the name of science is fun .

Step 1: Electrolysis of Water - an Explanation

Picture of Electrolysis of Water - an Explanation

This section is an explanation of the electrolysis of water, feel free to skip it if you don't find it interesting.

2H2O(l) = 2H2(g) + O2(g)

As everyone knows a water molecule is formed by two elements: two positive Hydrogen ions and one negative Oxygen ion. The water molecule is held together by the electromagnetic attraction between these ions. When electricity is introduced to water through two electrodes, a cathode (negative) and an anode (positive), these ions are attracted to the opposite charged electrode. Therefore the positively charged hydrogen ions will collect on the cathode and the negatively charged oxygen will collect on the anode.

When these ions come into contact with their respective electrodes they either gain or lose electrons depending on there ionic charge. (In this case the hydrogen gains electrons and the oxygen loses them) In doing so these ions balance their charges, and become real, electrically balanced, bona fide atoms (or in the case of the hydrogen, a molecule).

The reason this system isn't very efficient is because some of the electrical energy is converted into heat during the process. There have been reports of 50%-70% efficiency, but I doubt that is possible in a home environment. Anyway, enough with the boring stuff, lets go make some gas!

Step 2: Materials

Picture of Materials

****DISCLAIMER**** You are putting electricity into water. It has the potential to be dangerous. Do so at your own risk. Be smart about it. If you wouldn't touch it with your hands don't stick it in the water. If you're worried about it wearing rubber gloves will give some extra insulation. ****DISCLAIMER****

****DISCLAIMER**** Hydrogen is highly flammable and explosive (think Hindenburg). The amount we're making isn't extremely dangerous, but be careful. Flying shards of glass are never fun.****DISCLAIMER****

Separating Hydrogen and oxygen from water is really simple. It can be as easy as sticking two wires leading from a battery into water and watching the bubbles form. We however want to collect all the little bubbles, so its just slightly more complicated.

Things you will need:

@ (1) Med.Container - To hold water. Preferably clear so you can see whats going on.
@ (1 or 2) Gas Collecting Containers - A test tube, or an old soda bottle like me. Also clear. 2 if you want to collect both the hydrogen and the oxygen
@ (1) Power Source - I use a 12v 1000mA adapter, 9v batteries (in a series) and other sources work too. Bigger the power source, faster the bubbles form.
@ (2) Graphite Electrodes - Optional. You can stick a bare wire into the water, but it corrodes pretty quick. You can pull them out of a 6v Lantern Battery
@ Salt
@ Water

Step 3: Water and Salt

Picture of Water and Salt

Water alone is not a very good conductor. You need to add some sort of electrolyte. Regular old table salt works fine. Add as much as will dissolve into the water, and don't worry about it if there is some sitting on the bottom, it really doesn't matter. Pour this salt/water solution into your med. container, and also fill your 1 or 2 gas collecting containers

Step 4: The Tricky Part

Picture of The Tricky Part

Ok, this is the tricky part. You need to flip the gas collecting container(s) upside down in the med. container, so that no air is trapped in the gas container(s). I do it by holding my thumb over the hole, and flip it really quickly. Its not a huge deal if air is trapped, your hydrogen just won't be pure.

Step 5: The Electrodes

Picture of The Electrodes

Now take the two electrodes leading from your power source. The hydrogen will form on the positive electrode, and the oxygen on the negative. If you don't know which is which, turn on the power source and stick the electrodes in the water. The one with more bubbles is the hydrogen. Now stick the electrode underneath the gas collecting container. (turn off the power first) If you're having trouble making the gas collecting container stay up, and the electrode stay in the right place, tape it. Thats what I do anyway.

Step 6: Thats It!

Picture of Thats It!

Thats it! Turn it on, and watch it bubble. The amount of time it takes depends on how powerful your power source is. Stronger it is, faster it bubbles. Mine takes about 5 min for a test tube.

The electrodes do corrode if you don't have graphite, its pretty gross, but i don't think its dangerous. (don't quote me)

Here is a video of it bubbling:

Step 7: Further Ideas

When your gas collecting container is full, try lighting it. The hydrogen will give a very satisfying *POP*, and the oxygen won't do anything.

Here's a Video (sorry for not wearing a shirt =0 ):


For a bigger and better explosion, put both electrodes into the gas collecting container. Hydrogen needs oxygen to burn, and the ratio of 2:1 is the best ratio. That is what we get when splitting water. You will get a much more powerful explosion.

I've personally always wanted to make a model rocket powered on hydrogen. I know that there is one that is sold on the market, but I don't remember what its called. I'll look for it.

T3Hprogrammer and Kiteman suggest using baking soda rather than salt as an electrolyte. Table Salt (NaCL) has the potential of producing chlorine gas and sodium hydroxide when introduced to electricity.

JakeTobak suggests using platinum electrodes instead of graphite as graphite will chip, splinter, and corrode. They're as cheap as a couple dollars, and can be found on Ebay (thanks Kiteman)

Further Reading:

@ Homemade Hydrogen by Theodore Grey
@ Fuel from Water: Energy Independence with Hydrogen by Michael A. Peavey via
@ Water Car - How to Turn Water Into Hydrogen Fuel via


Rubens?? (author)2016-09-18

So what should I use instead of using salt to do it?

Mattphillips (author)Rubens??2018-01-09

Baking soda is a safer electrolyte, baking soda will create carbon dioxide, salt will create chlorine gas.

LukeB129 (author)Rubens??2017-08-22

KOH postassium hydroxide.

darkath (author)2016-04-20

Ok, so I am making a remote controlled blimp, and need to make hydrogen for the lift gas. is there any way to pressurize the hydrogen so it goes through the tube and into the blimp?

JuulP51 (author)darkath2016-11-27

If I add more graphite bars, does it give me more gas too?

LeoM115 (author)JuulP512017-12-10

If you keep the amount of bars even and make sure that all the positive bars have a corresponding negative bar, yes. But you might have trouble separating the hydrogen from the oxygen.

SeanW144 (author)darkath2017-02-28

Use a separate containment a tube running from the electrolosys container into another empty container. It wont become highly pressurised this way but youll be able to store more together meaning higher concentration. Then just make sure your ps is strong enough to separate the hydrogen at a high rate. Peace brother

IanM102 (author)darkath2016-04-23

Maybe a vacuum pump and an old spray can could do the trick, you could control it with an arduino.

MichaelK512 (author)2017-01-31

what should you use for the electrodes?

MichaelK512 (author)MichaelK5122017-02-07


SeanW144 (author)MichaelK5122017-02-28

Carbon rods are classically used... to the common man thats a pencil or in this case two of them... make sure to sharpen both ends. These rods can also be uses to create a spark gap filament for high voltage current which gives off a brilliant white light. Peace brother

LeoM115 (author)SeanW1442017-12-10

Or you can take the graphite out:

BilliN (author)2017-06-03

Can you breathe this oxygen as a human, without having any side effects?

LeoM115 (author)BilliN2017-12-10

Pure oxygen can cause cancer, but its pretty much safe.

RobertO160 (author)2017-11-09

This is the same method they use on submarines to create oxygen from seawater. But does anyone know what they do with the hydrogen?

LeoM115 (author)RobertO1602017-12-10

Probably just get rid of it

N Satya SrikanthN (author)2016-07-29


Oxygen forms at anode (the positive electrode), and Hydrogen forms at cathode (the negative electrode). Please change the battery connections and upload the correct schematic diagram for electrolysis

to are technically right but positive it when something has less electrons so it should be negative and if something has more electrons it is negative its stupid i thing positive should be negative and vise versa

DaveH223 (author)EthanL62017-11-18

Voltage flows from positive to negative current flows from negative to positive

Wrong way round cathode is positive which attracts cations... anode negative attracting anions

SeanW144 (author)SeanW1442017-02-28

I know this as I make batteries all day long and have been doing for several years. I learned from multiple sources including my own experiments. I wouldnt be able to make half the shiz I do if I didnt understand this

guymark (author)2016-02-28

An interesting article - thank you - though the comments are possibly more entertaining albeit for the wrong reasons :)

I would go along with suggestion of replacing the table salt with something else - and providing folks are careful, would suggest caustic soda while caustic (really?) is the best choice as other than sodium, it contains nothing more than oxygen and hydrogen.

Unless it acts purely as a catalyst and just "hangs around", I am guessing that baking soda may be adding carbon in the form of CO2 to the gas produced.

I may be wrong on that, but certainly sodium hydroxide will NOT contribute ANYTHING as a contaminate.

As for the HHO generators, I find valid points on both sides, in the first case, clearly generating the gas from an engine>alternator>battery power source is not going to yield more energy that is consumed in making it - so really not a fuel, more an inefficient conversion of one type of chemical energy into another - BUT I do believe it MAY be beneficial particularly on older cars.

The more out of sorts the engine is, the more I am guessing a whiff of something extremely volatile may be of benefit - even if the amount of gas added is totally insignificant from a "fuel" point of view, possibly it does assist in enabling a more efficient burn of the vapourised petrol. This could improve performance and economy while reducing emissions.

In much the same way that OLDER engines often seem to do rather well on LPG though a more moder efficient engine doesn't seem to yield a similar benefit (in both cases of course, LPG has a lower BTU than petrol but in older cars, results often seem to be better than optimal - which is almost certainly down to the fact that the old engine was struggling to burn the petrol/gasoline air mixture as efficiently as it was suppoed to - the lpg however provided an "easy more efficient combustion".)

So, I suspect an HHO generator may be of benefit on an older, tired engine with poor / fouled injectors etc or during VERY cold temperatures where the conventional fuel really is not being burned as well as it should be - the HHO gas may simply assist slightly in the volatility - as well as enabling the engine to run VERY slighlty leaner by adding a stochiometric mix to one which is normally kept rich. The more gas added, the closer to a stochiometric mixture, the leaner the burn. (I would expect a decrease in CO but an increase possibly in Nx ?)

In much the same way, that TINY amounts of acetone in a new car seem to do NOTHING at all of use (as you might expect as it has a lower BTU than regulalr petrol (gasoline) - yet in an old car, can sometimes make for a cleaner burn - nothing magical I suspect other than simply lowering the flashpoint slightly and making the fuel marginally more volatile?

Quite happy to be challenged on the above but you don't need to tell me how many reciepts you have for education (sorry, I mean degrees), just make a fair and reasoned point, I am keen to learn when I am wrong - but I have learned just as much from people who make "happy mistakes" and go "oh wow, that's interesting", than the people who aim never to make mistakes.

LukeB129 (author)guymark2017-08-22

It results in a faster burn rate and cleaner burn in the engine due to the points you mentioned, which may increases efficiency in older cars but on newer cars causes the oxygen sensor to be tricked and makes the car use excessive amounts of fuel.

StevenC17 (author)guymark2016-06-10

That was a fun read....;0)

Goku85 (author)2016-09-29

I am in the process of powering a little bike engine from the gasses. Will keep u posted

LukeB129 (author)Goku852017-08-22

Interesting. For a bike or just for fun? how are you storing the gasses?

ScottC190 (author)2016-07-09

I just taught Honors Chemistry again after not doing so for ten years. I used Calcium Nitrate as a catalyst. NaCl does frequently produce noticeable amounts of chlorine gas, and sodium bicarbonate (baking soda) does produce carbon dioxide with the oxygen, which negates the relighting or a wooden splint effect. I get a very good 2:1 ratio of Hydrogen to Oxygen, which seams to be rather pure.

AsaB6 (author)ScottC1902017-06-22

I built a multi cell electrolytic hydroxy gas generator system using stainless steel washers separated by nylon washers. The electrolyte I used was potassium hydroxide. I tried sodium chloride and baking soda as well. The potassium hydroxide does not produce CO2 or chlorine gas. It does not cloud up the water. It seems to allow faster more consistent production of hydroxy gas. I tested the explosive nature of the gas by filling a balloon with hydroxy gas and tossing into a camp fire. The explosion (actually implosion) was tremendously loud. It freaked everyone out around the fire. Any louder and I'm quite sure nearby structures would have lost their windows. Anyhow, the point is potassium hydroxide seems to work very well for extended periods of time.

ScottC190 (author)ScottC1902016-07-09

Of course, now I realize that the one tube is becoming very basic with CaOH and the other is getting rather acidic with nitric acid. Wear rubber gloves or your fingers may sting.

JeffC101 (author)ScottC1902017-05-28

With the setup in the picture, as the two gases fill the tops of each tube(left and right) does the water level in the centre change? ie does the gas displace the water or is it a balance? if it does displace, at what pressure? Is there enough pressure to push the gas out the top and through a tube to an engine? and once the gas moves out, I'm guessing the water is drawn back up the tube? I would like to build this but am low on funds for experiments

jeffclough (author)2017-05-13

Hi. Here's a corrected version of your first image. Your text was right about positive, negative, anode, cathode, and where each gas collects, but the picture just needed a tweak to remove the confusion. Please update your otherwise excellent article to use this new image. Thanks.

HappyInstructables (author)2016-10-16

BBC says oxygen will be at the positive node while you say negative. This is a possibly dangerous mistake on someone's part. Which is it?

Oxygen is anionic... negative

BBC is correct, nothing bad will happen you'll just think your oxygen is hydrogen and vis-versa. However another way of telling which is which is that at the electrode at which hydrogen is being produced there should be roughly twice as much gas compared to the electrode at which oxygen is being produced.

Nitr0 (author)2016-11-15

The diagram is wrong, the Anode is positive and cathode negative, and hydrogen is attracted to the cathode because it is an anion, which means that Hydrogen is positive, therefore it is attracted to negative. Besides that, the red side on the battery is usually positive and the black side is negative.

iLike2play2 (author)Nitr02016-11-30

Thank you. I got so hung up the diagram, I couldn't even get to the directions and came straight for the comments! :-)
fact check.

AlanB160 (author)iLike2play22017-02-04

Couldn't you PLEASE edit your diagram per Nitr0, to correct the errors before some kid gets it all wrong?

mn127778 (author)2016-12-29

Probably a typo, but you are very right. if you are aiming to make an explosion, then you should combine the hydrogen and the oxygen. because if you just have hydrogen, then the balloon pops, and the air has to combine with the oxygen in the air to catch on fire, whereas the balloon with the oxygen and hydrogen combined will not have to mix with air to blow up. it is alot louder, bigger, and way more dangerous when you blow that balloon up. DO NOT TRY THAT AT HOME!!!!!!!!!! TRUST ME, BECAUSE I KNOW!!!! OK!!! NEVER!!!!!!!!!!!

maximus0 made it! (author)2016-06-15

why does the water turn yellow after that

ScottC190 (author)maximus02016-07-09

Likely, you are making chlorine gas because you used table salt for your catalyst. It is also known as mustard gas due to its yellow color, and was used as a chemical warfare agent in WWI.; it's dissolving back into the water and turning it yellow.

Nitr0 (author)ScottC1902016-11-15

Chlorine isn't mustard gas. Mustard gas is C4H8Cl2S, chlorine gas is very reactive with moisture to create Hydrogen Chloride, therefore it wasn't used as an agent in chemical warfare. Maybe you're thinking about phosgene, which is COCl2, which smelled like freshly cut grass and was used in chemical warfare, and is 50% Chlorine by composition.

WillJ34 (author)maximus02016-10-28

Dissolved Chlorine gas, if you used a Chlorine salt

tommyfun (author)maximus02016-06-28

That's the chlorine from using table salt as an electrolyte.

ezhil selvan (author)2016-11-12

Why it produce bad oudor?

WillJ34 (author)2016-10-28

This is wrong, the -ve terminal of the battery should be going to the H2 and the positive to the O2

JasonP155 (author)2016-09-03

Electrolysis of brine is a chloralkali process and proceeds according to the reaction: 2NaCl + 2H2O → Cl2 + H2 + 2NaOH

That is, hydrogen and chlorine are produced in equal parts. But because chloride is oxidized to chlorine more readily than oxide or hydroxide are oxidized to oxygen, no oxygen is produced from the electrolysis of brine.

Much of the chlorine produced at the cathode, then reacts with the remaining sodium hydroxide forming sodium hypochlorite (aka bleach):
Cl2 + 2NaOH → NaOH + NaClO + H2O

Table salt dramatically increases the conductivity of the solution, thus allowing much more current flow which can make it seem like you're producing lots of gas, but you're mostly making chlorine and hot bleach and half as much hydrogen as you could be getting. Bottom like NO CHLORIDES! You're better off using baking soda or washing soda or even lye and increasing your supply voltage until you get the results you're after.

PS: if you can't find big enough carbon electrodes, you can also use lead.

GrantP17 (author)2016-08-18

Putting salt in the water can produce chlorine gas when electrified. I don't think it is enough to be dangerous(pool chemicals probably contain more) but better safe than sorry.

HobbyKIng123 (author)2016-05-10

will silver wire work best, or what is best.

jays130 (author)2016-04-18

it is possible to obtain petrol from hydrogen?

ShannonM99 (author)jays1302016-04-25

petrol, or petroleum by-products, are chemical chains of carbon and hydrogen. For this reason, they are all called hydrocarbons.

So, yes, you CAN build petrol from hydrogen and carbon, however, it takes energy to do so. Burning hydrogen directly, in combination with atmospheric oxygen, derives plenty of energy without going through the extra steps, waste, and expense to make more complex molecules.

The real problem with hydrogen is the difficulty of storing it. The molecules are so small and slippery, they tend to leak out any container you put it in. And making it dense enough to make carrying it portable for long trips is a further complication.

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