Hydrogen is the most abundant element in the whole universe.
And it's never destroyed, it just binds to other elements like 2 Oxygen elements to create water...
When you "burn" hydrogen its actually a reversing chemical process of combining it with other elements, when hydrogen is "burned" it gives off heat/fire as it recombines with oxygen or other free floating elements.
Because burning stuff gives an optical illusion of destroying something or making it smaller, it's really the opposite, as the "burning" material is dispersed widely out into a larger volume into the atmosphere in the form of a gas of some sort.. (co2 / water vapour etc)
With fuel-cells the electricity is created because of the electrons pull attached to Hydrogen wanting to join Oxygen to become water/H2O..
You can see here this ballon of hydrogen is already pooling water at the bottom due to the oxygen that was already in the ballon...
When the flame hits the hydrogen in the ballon it forces a fast reaction of the Hydrogen recombing to the oxygen in the atmosphere causing a splash of water and the release of a lot of heat in the chemical recombination process.
Instead of electricity being created all the potential energy is lost in the form of a heat explosion in the process recombining the hydrogen and oxygen atoms.
Air is mostly just 78% nitrogen and 21% oxygen with 0.04% being co2 and other stuff. So free floating hydrogen will attach to oxygen to become water vapour any chance it can get.
https://en.wikipedia.org/wiki/Atmospher ... omposition
Here is a rather new and nerdy video below of how they make PEM fuel cells.
PEMFCs are built out of membrane electrode assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers.
An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. https://en.wikipedia.org/wiki/Proton-ex ... _fuel_cell