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Researchers just discovered a massive 'jacuzzi bubbling with almost pure hydrogen' — a lucrative source of clean energy
(www.businessinsider.com)
This is a most excellent place for technology news and articles.
NOx and water vapor. If the hydrogen is not burned correctly, you get more NOx from burning it than you do burning natural gas.
https://www.thechemicalengineer.com/features/hydrogen-the-burning-question/
Luckily fuel cells don’t burn hydrogen.