I don't think any hydrogen vehicle in actual use has a fuel cell (and if there's any, it's an incredibly rare exception). They are all internal combustion engines.
Proton exchange membranes are very unreliable and expensive. They are also not power-dense, one that powers a bus will be very large.
Proton exchange membranes are very unreliable and expensive. They are also not power-dense, one that powers a bus will be very large.