However, a closer look at Fig.5 rev

However, a closer look at Fig.5 reveals an exceptional case that deserves further explanation. It can be seen that, when the air stoichiometry is increased to 4, the maximum power density point is attained when the inlet relative humidity at cathode is 60% instead of 20%. The high air stoichiometry is responsible for an enhanced drying of cathode GDL and GC, as shown by the reduced liquid water saturation and concentration overpotential in Fig. 7, which also undesirably drains water from membrane and decreases its conductivity. The combined effect of increased oxygen supply and water removal under a high air stoichiometry diminishes the role of concentration overpotential, and the fuel cell’s performance becomes dominated by ohmic overpotential. Hence, when such a high air flow rate is needed, the dehydration of membrane should be remedied (or the loss of water compensated) by increasing the inlet relative humidity at cathode.