fuel cells have a massive problem, it's called HYDROGEN yes there is absolutly shed loads of it here on eath problem is it's all bonded to other stuff, most economical way to get hydrogen is from natural gas and steam.
Fecking hot steem and natural gas in presance of a catalyst the oxigen in the water will react with the carbon in the natural gas provideing co2 and h2 problem is tat really dosent solve a lo of problems it needs quite a lot of energy to do still produces co2 and hydrogen is a PITA to store. to get a relativly useable amount ino a cylinder in gasious form needs about 5000 psi so ou need a really stong cylinder ( thats going to be heavy ) it'll take's about 50% of the energy hydrogen provides to get it upto 5000 psi
it also good at getting out due to is small size it can migrate through seals really well, the other option is cryogenic storage, pressure's not a problem but you need to keep it cold when the vechel isn't been used the only practical way i can see is allowing the stuff to boil off to maintain the required temp to keep it liquid.
so with all that shag and hasstel if it's going to be steamed out of natural gas just feed the engine the gas in the first place uch easyer and more efficent in the long run.
as for getting hydrogen out of water- good luck it's possible but needs loads of energy that energy has to come from somwhere, where is the question.
ethanol is easy storing and has sufficent energy density to be usefull, the passat happily munching E85 & E99 atm wasent hard to convert ether
