Overall and local effects of operating parameters on water management and performance of open-cathode PEM fuel cells

Water management in open-cathode PEM fuel cells is challenging due to direct supply of ambient air. In this contribution, the water transport mechanisms and local water distributions in open-cathode PEM fuel cells are studied using local current measurement and various electrochemical methods. The results show local membrane dehydration occurs and the water distribution is much uneven when current density is lower than 200 mA cm−2. As operating current increases, the water content of membrane increases rapidly until the membrane is fully hydrated and the local water distribution also becomes more uniform. Whereas, liquid water begins to accumulate in gas diffusion layer and catalyst layer when the current density is over 700 mA cm−2. Furthermore, the effects of operating conditions are investigated. On the one hand, when the current density is lower than 500 mA cm−2, improving temperature and air velocity can reduce cell performance as too much water is removed out of fuel cell, leading to membrane dehydration. On the other hand, when the current density is above 600 mA cm−2, increasing cell temperature and air velocity can improve cell performance by removing excessive water in pores of gas diffusion layer and catalyst layer. The experimental fuel cell achieves the best performance with the temperature of 45℃ and air velocity of 2.2 m/s.