Hothgor, Yes you can burn hydrogen to make electricity in turbines or ICE's. Combined cycle would probably get you up to 55% efficiency. But clean Hydrogen from electrolysis, as you suggest from nuclear plants, would be best used in fuel cells with higher efficiencies. The waste heat could drive the Haber Bosch process to make ammonia, which by the way is a very effective scrubber of fossil fuel exhaust from generating plants or cars.

The only fuel cell that I know of that doesn't use a platinum catalyst uses a sodium borohydride solution. All other fuel cells are grossly expensive and will never be adopted in any transportation vehicle outside of mass transit. I already mentioned the ammonia creation as a by product of this process, and we won't need the hydrogen to scrub fossil fuel exhaust if we adopted this scheme.