Research done at the Laboratory for Energy and the Environment at M.I.T. concludes that "even with aggressive research" the hydrogen fuel-cell car will be no more efficient than the diesel hybrid (a vehicle powered by a conventional internal combustion engine in addition to an electric motor and batteries that are charged on longer oil-fueled journeys) in respect to overall fuel consumption and greenhouse gas emissions by 2020. The point is made too that although hybrid-diesel cars are already in use, a huge arrangement of infrastructure will be necessary to provide hydrogen at fueling stations. Taken along with the shortage of platinum, which could at most provide enough fuel cells to run just a few percent of the 700 million or so vehicles on the world's roads now, I conclude that hydrogen is not going to get us out of the hole we are heading for in the next 10 years when world oil supplies begin to plummet.
The results of this analysis were published only a month after the US government made its pledge to a billion-dollar commitment to develop commercial hydrogen/fuel-cell cars and one year following the US government-industry programme to produce the hydrogen-fueled "freedom car". I do wonder what is going on sometimes. In comparison, the UK government is apparently committed to cutting CO2 greenhouse gas emissions while it has been claimed that by 2030 there will be three times the number of plane flights and it looks that there will be a new terminal at London's Heathrow Airport. Presumably this is in the interests of short-term money making because, ignoring the obvious inconsistency of more planes but less CO2 emissions (?), what fuel will be used to power all those extra planes when the oil-resource will be running low by then, even for our conventional volume of transportation - both by road and air?
The researchers do not disqualify hydrogen outright, and go on to comment that: "If auto systems with significantly lower greenhouse gas emissions are required in, say, 30 to 50 years, hydrogen is the only major fuel option identified to date." I would take issue with this, however, and suggest that making diesel from algae might be the answer. Thus would be completely sustainable, could produce much larger amounts of biofuel per acre than from growing crops, e.g. rape or even palm oil; would pull CO2 out of the atmosphere; not require the use of arable land or freshwater (and hence not impact on conventional agriculture e.g. growing crops for food), since it can be grown in saline tanks, and put anywhere; and if the machinery used for the farming and processing of algae-oil into diesel were run on a proportion of that that same diesel, the result would be a very favourable EROEI. It would also obviate the necessity of engineering a completely new (and gargantuan) delivery infrastructure for compressed hydrogen since this brand of diesel could be simply dispensed using the more conventional means of tanks and tankers. 96% the world's hydrogen (used to make fertilizers and in oil refining) is made from fossil-fuels, mainly natural gas, and that produces CO2; therefore, in order to "significantly lower greenhouse gas emissions" it would have to be made by electrolysing water using electricity generated from renewable resources (also as yet undeveloped on the necessary scale for the task), not fossil fuels as most of it is made from now.
The M.I.T. team has used fairly optimistic efficiencies for fuel cells that are quoted by some of its proponents, but the conclusions are no rosier regarding the wide use of hydrogen cars. As a matter of fact, opinion varies enormously over the viability of fuel cells, both in terms of their efficiency per se and their robustness under real operating conditions. It has also been pointed out that it is not sufficient to quote the efficiency of the fuel cell in isolation, but that of the whole vehicle under mechanical (road) conditions. When all involved is accounted for, a hydrogen car is not so much different from one powered by a diesel or other high-compression engine.
A hydrogen economy is a beautiful idea, and it might or might not come about in the fullness of time. Meanwhile, it is renewable liquid fuel that we need, to replace the source the modern world depends on utterly and relentlessly, namely crude oil, as its supplies begin their imminent dwindling.
 "Hydrogen vehicle won't be viable soon, study says." By Nancy Stauffer, M.I.T. News Office. http://web.mit.edu/newsoffice/2003/print/hydrogen-0305-print.html
 "Fuel Cell Efficiency: A Reality Check." By Dominic Crea. http://www.evworld.com/article.cfm?storyid=730
 See "Oilgae" Link (top left hand corner of this blog), which describes various aspects of turning algae into diesel fuel.