Odds of Getting In
If you've got the qualifications and experience, then you shouldn't have too much trouble finding work in the field. Being a fuel cell engineer is a very specific specialty for a mechanical engineer to have, and while some may fall into the career by happenstance, most will actively work towards being an alternative energy OG.
This doesn't just include what you know, but also who you know, and where they're located. While every state has their various research locations, the biggest employers can be found in places that have the largest green energy sectors, like California (source). To have the best chances, you'll want to be where the jobs are.
There isn't a lot of competition in the field. While you may have to search a bit after graduation to find the job, eventually an opening will come along. And the best part is, since being incredibly intelligent and good with machines is basically what you do, you can parlay your skills and education into a whole boatload of other mechanical engineering professions as well. It's time to start getting toasters to run on the crumbs they leave behind.