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I've looked all over the place to find a way for me to separate water without needing to put in salt. What I've found is you can separate water into hydrogen and oxygen through electrolysis (which needs salt to make the water conductive), radiation (which I don't want to use - this is a house project that I want to get into), thermal (the water needs to be hotter than what I can provide), and photobiological (looks cool - but it looks like it won't produce much).

There's a lot of things out there for electrolysis water splitting, but every single one looks like it needs salt. Can I initially provide salt to a water splitting machine, then never refill it and still split water? Is there anything else, in which I could put in the water to make it split, and not have to ever refill said thing?

Really, I want to build the machine, and not have to keep providing resources that I'm going to have to get - just provide the machine water and electricity.

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Salt is not needed. Salt merely allows the water to be somewhat more conductive.

The King of Random on YouTube has a great video on making one. All you need is electricity and water. https://www.youtube.com/watch?v=cqjn3mup1So

He uses sodium hydroxide, but this not needed. It will just be less efficient.

If you want to be more efficient, you can add an electrolyte like salt. Whatever electrolyte you use, should not be used up. However, if the concentration of electrolyte gets to high (after you have used up a lot of water) it will split it too. This is bad with salt, as you can end up with chlorine gas and sodium hydroxide, which can be nasty to deal with.

So, as long as you replace the water fast enough and don't put in too much electrolyte, it should be fine and you will not need to replace it often.

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Pure water is poorly dissociated - it means that it does not conduct electricity very well. Therefore, if you want to split pure water electrolytically, you would need to use a high current - not very safe in home settings. Table salt (or practically any other water-soluble salt) acts as an electrolyte - it dissociates in water and greatly increases its conductivity, making the electrolysis possible with low currents. Be careful though, if you use the table salt and apply a voltage of 1.5 V or more, you will not only split water, but also produce chlorine gas (toxic, corrosive and explodes on contact with hydrogen). It is safer to use sulfates, such as sodium sulfate, or even diluted sulfuric acid - your only products will be hydrogen and oxygen, and you won't need to add new portions of salt or acid every time. Sodium/potassium hydroxide will also work, but its solution absorbs carbon dioxide from air with time, and forms a carbonate. Sodium carbonate is also a good electrolyte but it will release carbon dioxide during the electrolysis, so you will get a mixture of oxygen and carbon dioxide on the anode if you use an old solution.

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