Effect of operating conditions and micro-porous layer on the water transport and accumulation in proton exchange membrane fuel cells

Accurate measurement of water transport in an operating proton exchange membrane fuel cell (PEMFC) and water accumulation in the electrodes is crucial for understanding the impact of operating conditions and transport layer configurations on cell performance. A water balance setup, based on in-line gas flowmeter, pressure, relative humidity and temperature sensors, was developed and demonstrated to track the real-time water transport and accumulation within operating PEMFCs. Current results indicate that changing operating conditions have a dramatic effect on the water transport across the membrane, while the ratio of water transported to produced remains relatively constant with current density. Under dry conditions, water moves from anode to cathode while increasing humidity and decreasing temperature enhance cathode to anode water movement. Adding a micro-porous layer (MPL) to the cathode gas diffusion layer (GDL) increases the water back-diffusion from the cathode to the anode at all operating conditions, but the increase is not very significant and only results in a prominent performance increase at 60 °C and 70% RH. The improved performance at 60 °C and 70% RH is likely due to: (a) increased water vaporization, since less water accumulation was measured in the electrode; and (b) creation of in-plane oxygen pathways in the MPL around localized liquid water blockages in the GDL. Based on these results, the use of different operating conditions might have been the key contributing factor for the different behavior observed when an MPL was introduced in previous literature.