When I was a grad student I had to run a lab for undergrads to make their own fuel cells. This was a drawing I made to explain the basic components and how they went together. The metal plates on the outside are the current collectors. At the center is the membrane-electrode assembly or the MEA. It’s a piece of solid electrolyte membrane that feels a bit like a piece of rubber. On each side is a small square of catalyst, usually platinum particles.
I have to tell you, I sort of miss painting platinum onto MEAs. However, I do not miss helping people put these together. Getting all that lined up and sandwiched together is harder than it looks.