IIRC, there are combustion engines fueled by hydrogen.
The problem with hydrogen is that you don't find it in free form ready for you to collect and use. You need energy to "extract" hydogen from other compounds (water being the most famous of them), and burning hydrogen is going to give you less energy back than the amount you put in to extract hydrogen in the first place.
And if you had that energy in the first place, then why not use it directly?
The ones who want hydrogen are the ones that want to keep the status quo of things as much as possible, as the hydrogen economy is very much compatible with the oil economy in terms of infrastructures (not to mention that you can extract hydrogen from oil too).
If you want to know in detail why the hydrogen economy doesn't make sense, follow this
link.
