Polymer electrolyte membrane water management

Because of its lower temperature and special polymer electrolyte membrane, the proton exchange membrane fuel cell (PEMFC) is well-suited for transportation, portable, and micro fuel cell applications. But the performance of these fuel cells critically depends on the materials used for the various cell components. Durability, water management, and reducing catalyst poisoning are important factors when selecting PEMFC materials. 

In PEMFC systems, water is transported in both transversal and lateral direction in the cells. A polymer electrolyte membrane (PEM) separates the anode and the cathode compartments, however water is inherently transported between these two electrodes by absorption, desorption and diffusion of water in the membrane.5,6 In operational fuel cells, water is also transported by an electro-osmotic effect and thus transversal water content distribution in the membrane is determined as a result of coupled water transport processes including diffusion, electro-osmosis, pressure-driven convection and interfacial mass transfer. To establish water management method in PEMFCs, it is strongly needed to obtain fundamental understandings on water transport in the cells. 

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. ... 

M. Watanabe, Y. Satoh, and C. Shimura. Management of the water-content in polymer electrolyte membranes with porous fiber wicks. Journal of the Electrochemical Society 140, 3190-3193 1993. 

Research, develop, assemble, and test a 50 kW net polymer electrolyte membrane (PEM) fuel cell stack system comprised of a PEM fuel cell stack and the supporting gas, thermal, and water management subsystems. The PEM fuel cell stack system will be capable of integration with at least one of the fuel processors currently under development by Hydrogen Burner Technology (HBT) and Arthur D. Little, Inc. 

The temperature of operation of polymer electrolyte membrane fuel cells tends to get higher, because certain advantages are faced, such as improved tolerance of carbon monoxide, the improved ease of water and heat management, and increased energy efficiency. However, several commonly used polymeric membranes cannot withstand the high temperatures. Therefore, there is a need to look for alternative materials. 

At present, polymer electrolyte membrane fuel cells and power plants based on such fuel cells are produced on commercial scale by a number of companies in many countries. As a rule, the standard battery version of the 1990s is used in these batteries, though in certain cases different ways of eliminating water and regulating the water balance (water management) have been adopted. 

M. Ji, Z. Wei, A review of water management in polymer electrolyte membrane fuel cells. Energies 2 (2009) 1057-1106. 

Many different types of fuel-cell membranes are currently in use in, e.g., solid-oxide fuel cells (SOFCs), molten-carbonate fuel cells (MCFCs), alkaline fuel eells (AFCs), phosphoric-acid fuel cells (PAFCs), and polymer-electrolyte membrane fuel cells (PEMFCs). One of the most widely used polymers in PEMFCs is Nalion, which is basically a fluorinated teflon-like hydrophobic polymer backbone with sulfonated hydrophilic side chains." Nafion and related sulfonic-add based polymers have the disadvantage that the polymer-conductivity is based on the presence of water and, thus, the operating temperature is limited to a temperature range of 80-100 °C. This constraint makes the water (and temperature) management of the fuel cell critical for its performance. Many computational studies and reviews have recently been pubhshed," and new types of polymers are proposed at any time, e.g. sulfonated aromatic polyarylenes," to meet these drawbacks. 

Abstract Most of the transport processes of a fuel cell take place in the gas diffusion media and flow fields. The task of the flow fleld is to uniformly distribute the reactant gases across the electrochemically active area and at the same time ensure an adequate removal of the reactant products, which is water on the cathode side in both polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). Gas diffusion media are required to supply the reactant under the land areas of the flow fleld at the same time, the gas diffusion media has to ensure a good thermal as well as water management to avoid any non-optimum conditions. Characterization tools for gas diffusion media are presented, flow fleld types and design criteria are discussed and the effect of both components on the performance of a fuel cell are highlighted. System aspects for different fuels (hydrogen, vapor-fed DMFCS, liquid fed DMFCs) are compiled and the different loss contributions and factors determining the performance of a fuel cell system are shown. 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

Okada, T., Xie, G. and Meeg, M. 1998. Simulation for water management in membranes for polymer electrolyte fuel cells. Electrochimica Acta 43 2141-2155. 

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