Polymer electrolyte membrane fuel Flooding

J. J. Baschuk and X. Li. Modelling of polymer electrolyte membrane fuel cells with variable degrees of water flooding. J. Power Sources, 86 181—196, 2000. 

Baschuk, J. J. and X. Li, Modelling of Polymer Electrolyte Membrane Fuel Cells with Variable Degrees of Water Flooding, Journal of Power Sources, Vol. 86,... 

Gerteisen, D., Heiknann, T., and Ziegler, C. Modeling the phenomena of dehydration and flooding of a polymer electrolyte membrane fuel cell. Journal of Power Sources, 187(1), 165-181, 2009. 

The presence of water is critical for operation but in current PEMFCs proper water management is a delicate issue and poor control can greatly reduce the efficiency of the device. An excess of water can flood the catalyst and porous transport layers impeding the transport of reactants and eventually drowning the fuel cell. At low water content, the polymer electrolyte membrane can become a poor conductor and the reactivity at the electrodes is affected. Local hot spots arising due to the inefficient operation result in early degradation of the cell. ... 

The performance of a polymer electrolyte membrane (PEM) fuel cell is significantly affected by liquid water generated at the cathode catalyst layer (CCL) potentially causing water flooding of cathode while the ionic conductivity of PEM is directly proportional to its water content. Therefore, it is essential to maintain a delicate water balance, which requires a good understanding of the liquid water transport in the PEM fuel cells. 

Water content affects many processes within a fuel cell and must be properly managed. Proton conductivity within the polymer electrolyte typically decreases dramatically with decreasing water content (especially for perfhiorinated membranes such as Nation ), while excessive liquid water in the catalyst layers (CLs) and gas diffusion layers (GDLs) results in flooding, which inhibits reactant access to the catalyst sites. Water management is complicated by several types of water transport, such as production of water from the cathode reaction, evaporation, and condensation at each electrode, osmotic drag of water molecules from anode to cathode by... 

The membrane has two functions. First, it acts as the electrolyte that provides ionic conduction between the anode and the cathode but is an electronic insulator. Second, it serves as a separator for the two-reactant gases. Some sources claim that solid polymer membranes (e.g., sulfonated fluorocarbon acid polymer) used in PEMFC are simpler, more reliable, and easier to maintain than other membrane types. Since the only liquid is water, corrosion is minimal. Pressure balances are not critical. However, proper water management is crucial for efficient fuel cell performance [6]. The fuel cell must operate under conditions in which the by-product water does not evaporate faster than it is produced, because the membrane must be hydrated. Dehydration of the membrane reduces proton conductivity. On the other hand, excess of water can lead to flooding of the electrodes. 

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