Fame
While your creations may one day end up powering every commercial vehicle in the United States, most of those who own and drive them will have no idea who you are. Heck, most people haven't even heard of Nikola Tesla, and he's the AC half the Tesla/Edison supergroup that made AC/DC a thing.
Fame for the lowly fuel cell engineer will come in the form of peer interest. If you develop a new method of oxidization that creates a 5% increase in efficiency and also smells like fresh strawberries, you'll probably be the toast of the next few alternative energy conferences.
You could also eventually go into teaching, where you can build a small following among students and faculty. Having a fan club at Stanford dedicated to the nerdy Instagrams you post should count for something, right?