What’s missing from this discussion is the cost; synthetic hydrocarbons are incredibly expensive — think $45/gallon.
That may come down some, but people are going to electrify whenever possible instead of using e-fuels like this for cost reasons.
If there’s enough excess capacity of clean, renewable energy sources like wind and solar, that it can be converted into portable fuel . . . why hydrogen?
Its hard to contain, embrittles everything it touches, in gaseous form its density is low so its tanks need to be huge but in liquid form it needs to be kept unreasonably cold and is still low density and requires oversize fuel tanks, and its explosive when it mixes with air - not just flammable, but explosive.
Why not use that clean energy to pull CO2 out of the air and use it to build new hydrocarbon liquid fuels that are compatible with existing infrastructure?
Totally, if you need it use the century old, high density, well understood fuel, it’s just good engineering. Doesn’t need to be carbon negative. Even rockets are using methane these days…
There are probably use cases for hydrogen, but they’re likely large installations, either fixed or trains / ships. Toyota spent a decade trying to make it smaller and failed.
It could be a little carbon negative, in the way planting trees is a little carbon negative.
Sourcing carbon from atmosphere and hydrogen from water to make liquid fuel would pull carbon out of the air and put it into your gas tank.
Methane is easier to work with than hydrogen, but it still needs to be kept colder than what’s practical. If it turns out that propane is much cheaper to make from (renewable energy + atmosphere + water), relative to the cost of making liquids like diesel, kerosene, or gasoline, then propane might be a winning choice for renewable transportation fuel.
Batteries have an environmental impact too. I am no expert, but I can see why researchers are trying to find alternatives.
