Experimental Investigation of Air Relative Humidity (RH) Cycling Tests on MEA/Cell Aging in PEMFC Part I: Study of High RH Cycling Test With air RH at 62%/100%

The effect of high air relative humidity (RH) cycling (RHC 62%/100%) on the degradation mechanisms of a single (5 x 5?cm2) proton exchange membrane fuel cells was investigated. The cell performance was compared to a cell operated at constant humidification (RHC?=?62%). Runs were conducted over approximately 1,500?h at 0.3?A?cm2. The overall loss in cell performance for the high RH cycling test was 12 mu V?h1 whereas it was at 3 mu V?h1 under constant humidification. Impedance spectroscopy reveals that the ohmic and charge transfer resistances were little modified in both runs. H2 crossover measurement indicated that both high RH cycling and constant RH test did not promote serious effect on gas permeability. The electroactive surface loss for anode and cathode during high air RH cycling was more significant than at constant RH operation. The water uptake determined by 1H nuclear magnetic resonance within the membrane electrode assembly (MEA) after high RH cycling was reduced by 12% in comparison with a fresh MEA. Transmission electron microscopy showed bubbles and pinholes formation in the membrane, catalyst particles agglomeration (also observed by X-ray diffraction), catalyst particles migration in the membrane and thickness reduction of the catalytic layers. Scanning electron microscopy was conducted to observe the changes in morphology of gas diffusion layers after the runs.