It is an electrochemical process. It is similar to other electrochemical processes, like charging batteries. The better question is how did people get convinced it wasn't efficient? Likely, this is the result of some kind of corporate FUD, possible from oil companies originally, but now more likely from battery companies.
If you believe the most efficient listed numbers from Wikipedia, it's roughly 50kWh/1kg of hydrogen to produce. That excludes any cost to transport, store, etc.
The Toyota mirai gets something like 60mi per 1kg of hydrogen fuel. Which, translated, gives you an efficiency of roughly 800Wh/mi. Excluding transport and storage costs. A modern EV gets roughly 250Wh/mi, and incurs no storage costs or transport costs.
You're number bending. You cannot move continuously change a few percentage points at each step. You can create whatever outcome you want by doing this.
The Mirai gets 74 miles per kg of hydrogen according to the EPA. That's ~560 Wh/mi.
And no, a "modern EV" does not get 250 Wh/mi unless your talking about a smaller car than a Mirai. A good point of comparison might be the BMW i5 which gets ~320 Wh/mi. This is also from the outlet, and does not include upstream energy losses.
What people realize from honest analysis is that FCEVs and BEVs are around 1.5-1.75x of each other. But then people have realized that upstream losses, especially the need for energy storage for renewable energy, greatly undercuts this argument. For season energy storage, the mechanism is literally just burning/reacting hydrogen for electricity production.
So in reality the gap in efficiency is small, and as we switch to greener energy sources this gap shrinks.
It's a bit inefficient, but I think state of the art is over 80% commercially and 95+% in the lab. Of course, then you have to compress and transport and store it.
Can be, but isn’t. The most cost effective way of generating hydrogen is by cracking it out of petroleum. That won’t change anytime soon.
“Green hydrogen” is a lie created by the petroleum industry.
That mirrors similar rhetoric surrounding wind and solar just before they hit large-scale deployment. As it turns out, sustainable resources tend to be much cheaper than unsustainable ones.