I think this is important to note about hydrogen as a 'clean' fuel source:

> Today’s hydrogen is “gray,” made by reacting methane with steam at high pressures or using fossil fuels in other ways. Those processes emit some 900 million tons of carbon dioxide every year, almost as much as global aviation. In principle, that carbon could be captured and sequestered underground, yielding “blue” hydrogen. But most hopes rest on “green” hydrogen—using renewable solar or wind power to split water molecules into oxygen and hydrogen with electrolyzers.

_Today_, it is not a clean source of energy for vehicles.