Electrolysis of water

I have a few questions for the electrolysis of water.

If 4 Litres of water is used and lets say for example a 9 volt battery is used. How much hydrogen and oxygen will be produced per second in terms of molecules?

Also if salt is added to the water to speed up the process, how much salt would be needed and would the products from the electrolysis change?

Please answer
Thank you

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