If you can produce hydrogen without carbon emission, then you can also use that hydrogen and produce synthetic fuel without carbon emissions like Fairandunbiased said in #1078. Synthetic fuels can be burned in existing engines and transported using existing infrastructure. There's really no reason to use hydrogen itself as a fuel.Well, that's the wrong way to produce hydrogen then. There are ways to produce hydrogen without carbon. This beats all the carbon burning power sources in long run.
Making hydrogen production more efficient and more env-friendly is one side of the coin. The other is to find and test the right use-cases. I don't see why these two tasks cannot go in parallel.