It can behave as anode and cathode depending upon another electrode taken.
(a) When it acts as anode reaction will be :-
H2 ---> 2H+ + 2e
Representation will be :- Pt, H2 (1atm.) / H+ ( 1M)
(b) 2H+ + 2e- -----> H2
Representation will be :- / H+ ( 1M) / H2 (1atm.), Pt
