[random rant directed at no one]
The problem I foresee with H2 is that making it is a problem unto itself. The amount of energy you get by combining H2 and O2 in combustion is the exact same energy it requires to split it. It's a law of physics. Right now we can dig up pre-existing HCs and distill it into gasoline or diesel at the expense of killing the planet, and people are making massive money on that market.
I agree that we need to stop burning HCs for energy, but replacing it with an incredibly explosive gas that requires massive amounts of energy to produce is not a net win.
I've read a few books on biofuels because nerd reasons. Even if we converted every single U.S. farmed plant into alcohol, (this was a book from about 10 years ago), it's estimated that we would not only not have any food in the U.S., we would still fall short of demand by 30x. We're a thirsty bunch.
If we converted all of the farmed fats into bio diesel, we would still be way behind. You have to remember that at best, you can only get about 13% of a crop yield as alcohol. It's a time and labor-intensive process. Using some algaes, you can get up to 60% of crop yield as bio diesel, it takes a few hours, and emits no CO2.
Here's my main thinking: We are taking carbon from below the biosphere, burning it, and dumping it IN the biosphere. No amount of cleaning it up is the answer. The answer is taking the carbon from here, then we can burn it with near impugnity because whatever we burn has A) already existing up here for billions of years, and B) first had to be scrubbed OUT of the air by plants.
I'm all for bio fuels like alcohol, but it's far from sustainable. Bio diesel is much closer to sustainable, but still not enough. H2 requires as much energy to produce as you get back by combusting it, and even then most of what you combust is lost to friction, heat, and pumping. EVs provide a nice step, but until we get away from our primary electrical source being burning fossil fuels, it's not a proper end game.
The only solution I see as sustainable is EV and a massive infrastructure change to renewable energy, which so far has been mostly thwarted by big oil. For a long time there was a billboard on the turnpike that read "Sun sets. Wind dies. Clean coal power is the answer." Really? A few million years of history shows that the sun comes back every morning, and the wind won't just disappear forever... unlike coal. They coal industry is still pushing the narrative that sending workers into a deadly mine to harvest dead carbon is the sustainable answer.
This whole thing kind of boggles my mind. When we discovered that Asbestos was dangerous, we didn't have the Asbestos Local 212 go on strike, and manufacturers didn't scream "who will think of the jobs?" They were like "E36 M3, we gotta stop killing people."
[/rant]