According to that Wickepedia article, hydrogen fuel cells have theoretical max efficiency of 83%. Even though the pratical efficiency for fuels for automibiles will be significantly below this it will still be quite good. Also, fuel cells capable of displacing the genset in the Volt are very expensive today but it is very conceivable there costs can come down to below the genset. The difficult issues that do not have good answers for yet are effectively isolating, storing, and distributing the hydrogen. This is where the efficiencies and costs are difficult to resolve. Personally, I believe hydrogen fuel cells are very cool and will have their places, just not in my car. I have no interest in trading gas for hydrogen as my feul until we have a surplus of inexpensive, clean energy that would otherwise be wasted.
Don't kid yourself. GM and the other automakers saw Hydrogen feul cell research and prototypes as a lesser of 2 evils: this or significant production runs of EV's. By the way, the taxpayers are footing the majority of this bill.
