Water management is a central issue in the development of polymer electrolyte fuel cells (PEFCs): liquid water could considerably increase the oxygen transport resistance and hence the transport polarization whereas dryness dehydrates the electrolyte membrane, raising the Ohmic voltage loss. PEFCs produce water during operation and the electro osmosis enlarges the water imbalance between the anode and cathode sides, making water management a complex operation that requires a careful treatment. Issues such as diffusion media dewetting, anode rehydration, and internal humidification have received much attention in recent years. Modeling, numerical simulation, and advanced imaging techniques are capable of revealing details of transport phenomena, and are a powerful tool for elucidating water management.

In this talk, I will cover the below subjects which are the major contributions of UC Irvine to water management: 1.) nonisothermal two-phase flow modeling; 2.) transient dewetting of gas diffusion layer (GDL); 3.) theoretical approach of defining control parameters to characterize two-phase flows; and 4.) experimental evaluation of two-phase flow in PEFCs using neutron radiography. In 1.), a nonisothermal two-phase model, accounting for vapor-phase diffusion and heat pipe effect, was developed and implemented to investigate liquid water distribution. The model was validated in detail against liquid water distribution across GDLs. In 2.), a transient model was developed to capture the phase change and interface movement in PEFCs. A case study will be presented to show the timescale of material dewetting at different regions of GDLs. In 3.), A dimensionless parameter Da₀ will defined to characterize the in-plane two-phase region. When Da₀ is over 1, part of the GDL region is free of water due to waste heat production and evaporation. A liquid-free GDL region is defined and related to Da₀. Impacts of operating temperatures, GDL thermal conductivities, and current densities on the region will be discussed. In 4.), I will present an in-situ study to examine the water content in PEFCs using neutron radiography. Various conditions such as different PTFE loadings in the GDL including the micro-porous layer (MPL), different flow fields (single-channel and quad-serpentine channels), and co-/counter-flow configurations are investigated.