Fact: The U.S. power grid has continually reduced its overall emissions for decades now.
Fact: Electric vehicles produce less overall emissions than a 35mpg car, even on the dirtiest grid in the U.S, and most EVs are operated on much cleaner grids.
Fact: Over 1/3 of EV drivers own enough solar generation to offset the power used in their cars, making them truly zero emissions.
Zero-emissions electric vehicles exist now, if you have the money or lifestyle to fit it. I too think it will be a great day when hydrogen cars actually compete with battery-electric vehicles. But the obstacles we have to solve before then are many:
1) invent a way to convert electricity into hydrogen that actually approaches the efficiency of batteries, if not equaling it, instead of making it out of methane like we do now or wasting half your power in electrolysis.
2) build hydrogen fueling stations everywhere before a solid base of users exists to pay for it.
3) convince the public that hydrogen cars won't explode like the Hindenburg (stupid but important).
4) make them cheaper than an equivalent battery-electric car, because by the time all that gets done BEVs will be so far ahead you will wonder why you bothered with hydrogen at all.
Once Tesla has created a super-cheap source of grid storage batteries, everyone with an electric car can get solar and go off the grid. Then the power plants and centralized distributors will be forced to shut down. Then local grids will spring back up so people can use communal backup generators on cloudy weeks, but we will never again need the complex monstrosity of our present power grid because all generation will be local. We already have new factories installing enough solar and wind to power themselves, so it's only a matter of time before the grid becomes redundant and uneconomical to maintain.