What's wrong with hydrogen? You can produce it with renewables, it basically works with existing IC technology and the exhaust is just water. The only hangup is the energy/volume ratio, which is an area of ongoing research.
It seems like a great fit for...a lot of use cases. (if we can get over some of the storage hurdles)
》Water vapor is known to be Earth’s most abundant greenhouse gas
https://www.nasa.gov/topics/earth/features/vapor_warming.htm...