Water management is one of the key

Water management is one of the key issues for efficient and stable operation of proton exchange membrane fuel cells (PEMFCs). Water flooding easily occurs at the elevated operation current density, especially at the downstreaming of the flow channel where the generated water should flow out. Proper water management should meet the needs of adequate membrane hydration and the avoidance of flooding in the catalyst and gas diffusion layers. Flooding will not only lead to performance losses due to the hindered reactant supply, but also the safety issue because of the cell reversal. A partial flooding model is proposed to investigate the effect of the porosity on the performanceofa PEMFC.The results showthathightemperature is conducive tothe suppression of flooding at low relative humidity, and flooding would lead to the deterioration of mass transfer due to the porosity decrease of gas diffusion layer, especially at high current densities. Partial flooding won’t significantly affect the power generation capacity of the fuel cell, but will cause uneven distribution of current density, resulting in an adverse influence on long-term operation. Moreover, the performance would suffer serious degradation with completely flooding. Once the area inside the PEMFC is seriously flooded, the current density in non-flooded area is up to 4.7 times higher than that in the flooded area, and the performance is difficult to recover even if increasing the stoichiometry of reactants. The study illustrates the importance of the water management at the downstreaming of the fuel cell.