“…This hydrogen pumping phenomenon has been recognized when the oxygen supply is insufficient in one or several cells inside a galvanostatic discharging PEMFC stack, as discussed in literature [42e44]. Under conditions where the air supply is sufficient, however, to be best of our knowledge, no research has reported this phenomenon except for the experimental work of Mitsuda and Murahashi [45] in a phosphoric acid fuel cell (PAFC). In their work, a single PAFC was tested at a constant current density with insufficient fuel supply, and unexpected hydrogen gas was detected in the cathode exhaust.…”