Question: what are the half equations for hydrogen fuel cells?
Answer: 2H2(g) + O2(g) ==> 2H2O(l)
Its a very exothermic reaction, releasing lots of heat energy when burnt, remember the 'squeaky pop' lit splint test for hydrogen!
The hydrogen - oxygen fuel cell is non-polluting, since only water is produced.
But know how to think of it in terms of bond breaking and bond making.