Water Management in a PEM Fuel Cell by Material Design and Engineering of the MEA

PEMFCs depend on proper water management to obtain high power density and energy efficiency. Traditionally, water management has been addressed by system design and engineering. That is, by adding auxiliary systems to the basic fuel cell system to provide humidification to the anode and remove water from the cathode. This approach adds significant complexities and costs and reduces the overall efficiency of the PEMFC system. To simplify the complexity of the PEM fuel cell system, an alternative approach is explored. In this new approach, components with the right properties will be used in the membrane and electrode assemblies so that the zero-net-water-transport-across-the-membrane condition can be achieved. This presentation discusses the components and the properties required to achieve the condition of zero-net-water-transport-across-the-membrane. Introduction Proton Exchange Membrane (PEM) fuel cell is being considered as a power source for a variety of applications because of its high efficiency, simplicity in design and operation, and environmentally friendly characteristics. Significant efforts in multiple areas in the past two decades have brought this technology to a point that commercialization in a near future is now considered a possibility. The biggest obstacle to the commercialization of this technology currently is its cost. If the cost issue could be addressed, the remaining technical issues such as durability and low temperature startups would be quickly resolved. There are mainly two reasons for the current high cost of the PEM fuel cell system. The first one is due to the cost of the materials. The second one, arguably the more significant one, is due to the complexity and the cost of the auxiliary systems needed to operate a fuel cell system. These auxiliary systems are used mainly to provide proper gas, water and thermal management to the system. Of the gas, water and thermal management requirements, water management is believed to be the most crucial one. PEM fuel cells depend on proper water management to obtain high power density and energy efficiency. During operation water is dragged from the anode to the cathode by electro-osmosis leading to dehydration at the anode. Concurrently, in addition to water transported from the anode by electroosmosis water is also generated at the cathode by the oxygen reduction reaction. When the water created in the cathode is not properly removed its accumulation leads to poor fuel cell performance by blocking the gas pores used for oxygen gas transport and forming an additional transport barrier over the reactive area. In some applications and conditions, cathode humidification is desired. Traditionally, water management has been addressed by system design and engineering. That is, by adding auxiliary systems to the basic fuel cell system to provide humidification to the anode and to remove water from the cathode. This approach has added significant complexities and costs to the system. Furthermore, these auxiliary systems reduce the net power output of the fuel cell system leading to lower conversion efficiency. Some of the traditional approaches of water management in PEM fuel cells are listed below. Old Paradigm: Water Management by System Design and Engineering Anode/Cathode Gas Humidification: To provide humidification to the anode/cathode, various humidification strategies and systems have been adopted. Figure 1 lists some of the strategies employed by various fuel cell developers. Each system has its own advantages and disadvantages. Regardless of which one is used, additional complexity, cost and parasitic power loss are involved. Figure 1. Humidification strategies used in PEM fuel cells. H 2 H 2O (l)