Works with/for hydrogen fuel cells

"Works for" usually names your employer or states your purpose. "With" is 100% the common choice, even when describing people. "She works with handicapped children." "I work with a team of heart surgeons."

I work for a better world.

I work for the fire department.

I work to make the streets safer.

I work with very delicate instruments.

Thanks, Avangi.

To make sure I understand it right, does "work with hydrogen fuel cells" in question mean "works at the department of hydron fuel cells?"

It's not very specific. There may not be such a department. Hydrogen fuel cells are still in the experimental stages. He may be a scientist working in a laboratory where research is being conducted on the development of the cells. It may be part of a university, or an automotive company or any big company interested in developing new energy sources.

Thanks, Avangi.
I still can't pindown the meaning of "work with" in question. Does it amount to "work on hydrogen fuel cells?"

Right.

"I work with high compression racing engines." I spend my days in their close company, and I am intimately involved with them. (But it doesn't necessarily mean they return the favor by cooperating with me.)