I was always fascinated by chemistry and the oil industry, I actually had to read about it in books. Not only does the petrol chemical industry make all the hydrogen, they make ammonia, the reason why humanity is capable of making so much ammonia today is it sustains modern agriculture with synthetic fertilizer ammonium nitrate or anhydrous ammonia directory injected into the top soil.
The oil industry already possesses the most efficient and cheapest way to Crack hydrogen.
If there was some cheaper, greener, renewable method to make H if the oil industry doesn't invent it, they will scale it up to industrial levels.
Low temperature electrolysis is only viable if you have a huge surplus of electricity that you don't have any use for. This is one thing commercial nuclear power would be good for. Most reactor designs like to be ran at 90% to 100% for months at a time, they do not like to be stopped and restarted or ran at lower power level.
Is going to get you.