Power
If fuel cell engineers had their way, American infrastructure would already be reliant on renewable and alternative fuel sources. Obviously, this is not the case. While car manufacturers and others are slowly coming around to this new technology, society still runs mostly on oil and coal. The people who have the most say in the discussion—energy executives, industrialists, and your friendly neighborhood U.S. Senator—see no reason to change this any time soon.
This isn't to say that fuel cell engineers are without power. Besides the chemical reactions they deal with on a daily basis, the field is rife with powerful thinkers and even more powerful ideas. There is a definite space in society for your work in which the power of your thoughts is transformed into actual tangible results.
If your research and development eventually leads to a combustion-free commercial airliner, you'll have legitimately changed the aviation game with a simple combination of wit, determination, teamwork, and (perhaps most importantly) caffeine.
Typically, the most powerful people in an alternative energy company are the ones who own it. You might be a genius at figuring out how to turn a potato into the next big fuel source, but you need someone like Elon Musk or Richard Branson to promote and market it. They also get most of the credit and cash, but at least when people ask you what you do at neighborhood BBQs, you can talk about your boss. Who doesn't like to do that?