But there's always a catch when you fiddle around with thermodynamics and energy efficiency. In hydrogen's case, it's a problem of production. Hydrogen may be the most plentiful element in the universe, but unless you feel like dropping by the surface of the sun (bring a cold drink and thick-soled shoes!), you're not going to find the element anywhere for free. Hydrogen here on Earth is always bonded to something, which means it needs to be extracted, a process that's expensive, time-consuming and takes an enormous amount of energy.
Currently, most of our hydrogen is produced through electrolysis or by stripping it from natural gas in a process called steam reforming. (Natural gas is a fossil fuel, too.) While steam reforming is the most common method of industrial hydrogen production, it requires a good deal of heat and is wildly inefficient. Hydrogen produced by steam reforming actually has less energy than the natural gas that steam reforming begins with. Plus, unlike hydrogen fuel cells, the process produces pollution -- so it's actually more energy efficient just to use the hydrocarbons themselves as fuel.
However, there's hope. While we still haven't found a viable way to get hydrogen on the cheap, things are getting better. The cost of materials is falling, and there are several potentially easier ways to collect it, like harnessing hydrogen-producing algae and using methane from landfills. A hydrogen-powered future may be in sight, or it's at least a speck on the horizon.