Study of sulfur dioxide crossover in proton exchange membrane fuel cells

As one of the most deleterious impurities to proton exchange membrane fuel cells (PEMFCs), sulfur dioxide (SO 2 ) in air can pass through the membrane from the cathode to the anode and poison the catalyst of the two electrodes. The phenomenon of SO 2 crossover is investigated electrochemically in this paper. The influences of SO 2 concentration, relative humidity, gas pressure and current density on SO 2 crossover are discussed. Experimental results reveal that the anode tends to be poisoned heavily with the increasing concentration of SO 2 in the cathode. The coverage of the anode catalyst by SO 2 permeating from the cathode enlarges with the decreasing relative humidity in the anode. The rate of SO 2 crossover from the anode to the cathode is promoted at high current density when SO 2 is directly introduced into the anode side instead of the cathode side, which can be ascribed to the electro-osmotic drag effect. Gas pressures show no obvious effects on SO 2 crossover. A co-permeation mechanism of SO 2 with water is deduced based on the overall analysis.