The effect of the clamping pressure and the relative humidity on gas crossover is studied in this research. It is central to this paper that the effect of the operating parameters on the hydrogen crossover is analyzed for various current densities. The performance and the hydrogen crossover rate are measured simultaneously according to the different clamping pressure and relative humidity at each current density. The effect of both parameters on the system performance coincides well with other researches. The higher hydrogen concentration and crossover rate are detected for the elevated clamping pressure and relative humidity. Interesting result from this experiment is that almost even hydrogen concentration at the cathode is detected with respect to current densities for all cases. When transforming this data with the flow rate of air supplied, the hydrogen crossover rate is gradually increased as the current density is increased. It means that the mass of the hydrogen gas transferred is increased for higher current densities. (C) 2016 Elsevier Ltd. All rights reserved.