I went back and re-read the article and I still can't see where JJ claimed that hydrogen powered cars were impossible.
This debate always degenerates into those who know how to do an energy balance and those who don't. Hydrogen is a storage medium for energy. It is not a source of energy...at least until we find some vast hydrogen reservoir somewhere.
We mine energy now. In doing so, we release the primordial energy stored after billions of years of energy storage by the ecosystem. This includes the storage of energy in rotting plants that formed crude oil and natural gas, the energy from the fission of elements created in the formation of the earth, from the primordial fusion of the sun, the rotational (gravitational) energy of the sun and moon and the primordial heat from the creation of the earth (geothermal). There is no free lunch and no free energy.
Where does your hydrogen come from?