my understanding of the process of the proton exchange membrane fuel cell was that the input is H2 and is ionized catalytically at the anode by means of the platinum. this leaves H+ ions, which travel through the polymer membrane, and e- which are forced to travel along an external circuit, producing the power output. from there the H+ are supposed have crossed the cathode, which continues to confuse me, and combine with incoming O2 and the e- of the finished circuit, resulting in H2O. how does the platinum have this effect and what makes it more suited to this function than other elements or compounds. as a bonus question, why do the protons cross the cathode instead of being attracted to it?