Hydrogen is pretty common, both in the Universe (roughly 75% of the baryonic mass of the Universe is H) and on the Earth (it makes up 15% of the crust, oceans included which is what matter to us in terms of being able to get it).
It is also a very good fuel but the downsize is that it is bounded to other atoms in a very strong coupling. Breaking this coupling to free H is costly. Splitting H from Oxygen, O, in a water molecule is done today using platinum as a catalyst and that is pretty expensive.
Most of today's production of H starts from Methane, CH4, and therefore requires fossil fuels hence this system does not fulfil our goal of replacing fossil fuels with H.
Researchers at Rutger have worked out a way to split water molecules using carbon nanotubes instead of platinum, thus significantly reducing the cost.
The splitting takes place through electrolyses, which of course requires electrical power but this can be generated using renewable sources, like photovoltaic and wind turbine, so you can produce H in a clean way. The effectiveness of the carbon nanotubes catalyses compares to the one based on the much more expensive platinum.