Researches On The Distribution Properties And The Factors Affecting The Performances Of The PEMFC With Anodic Dead-end

Proton exchange membrane fuel cells (PEMFCs) under anodic dead-end operation can obtain a high hydrogen utilization, and if PEMFCs is well designed, the fuel humidification systems can be simplified. However, when air is used as oxidant, the water and nitrogen can cross over the membrane owing to the concentration gradients between the anode and cathode. The accumulation of the water and nitrogen could lead to uneven fuel and current distribution. What’s worse, it could cause local fuel starvation and carbon corrosion, following irreversible performance decay of the PEMFC. Consequently, the studies of the local distribution characteristics, performance degradation mechanism and the influences of the operating condition on purge interval are of great significance to improve the performance and lifetime of PEMFC with anodic dead-end.In this paper, the local fuel and water distribution characteristics and their effecting factors are investigated. The main contents and their conclusions are as follows:(1) The local distribution characteristics of the PEMFC with anodic dead-end were experimentally explored with measurements of current distribution, local potentials and carbon support micro-structure. Experimental results show that during anodic dead-end operation, the current distribution is uneven, firstly degrading at the area near the outlet, and then proceeding to the region near the inlet with time. The complete fuel starvation near the anode outlet brings about high cathode potential up to1.35V and rapid carbon corrosion. As the levels of local fuel starvation vary on the location in anode along fuel flowing direction, the degradation of carbon is uneven. SEM images demonstrate that a significant thickness reduction and porosity collapse occur at the cathode electrode due to local fuel starvation near the anode outlet.(2) With the purge interval as key parameter, the influences of operating conditions on purge interval were investigated. Experimental results show that, at the same condition, the purge intervals increase with increasing anode gas pressure and cathodic air stoichiometry, and decreases with the increasing cell temperature, relative humidity and current density.(3) The experiments in a visual fuel cell with oxidants of different oxygen concentration and fuels of different hydrogen concentration reveal that, during the experiment, the dominant factor affecting performance decay under dead-ended operation is nitrogen crossover rather than the water accumulation in the anode channel.