Fuel cell critical specifications

Direct-methanol fuel cells (DMFCs) have attracted considerable attention for certain mobile and portable applications, because of their high specific energy density, low poison emissions, easy fuel handling, and miniaturization [129,130], However, the methanol permeation through electrolyte membranes (usually called methanol cross-over) in DMFCs still is one of the critical problems hindering the commercialization [131,132], Nafion , a... 

All the examples discussed in the following subsections are meant to be taken simply as an indication of how important it is to determine the correct hydro-phobic content for a specific DL. It is also critical to take into account all the possible operating conditions in which the fuel cell will function because these parameters will have a direct impact on the overall performance of the cell. 

Polymer electrolyte fuel cell (PEFC) is considered as one of the most promising power sources for futurist s hydrogen economy. As shown in Fig. 1, operation of a Nation-based PEFC is dictated by transport processes and electrochemical reactions at cat-alyst/polymer electrolyte interfaces and transport processes in the polymer electrolyte membrane (PEM), in the catalyst layers consisting of precious metal (Pt or Ru) catalysts on porous carbon support and polymer electrolyte clusters, in gas diffusion layers (GDLs), and in flow channels. Specifically, oxidants, fuel, and reaction products flow in channels of millimeter scale and diffuse in GDL with a structure of micrometer scale. Nation, a sulfonic acid tetrafluorethy-lene copolymer and the most commonly used polymer electrolyte, consists of nanoscale hydrophobic domains and proton conducting hydrophilic domains with a scale of 2-5 nm. The diffusivities of the reactants (02, H2, and methanol) and reaction products (water and C02) in Nation and proton conductivity of Nation strongly depend on the nanostructures and their responses to the presence of water. Polymer electrolyte clusters in the catalyst layers also play a critical... 

It is critical to minimize the component manufacturing variations in order to build a reliable PEM fuel cell system. We demonstrated that even within the same commercial MEA sample, the thicknesses of the electrode layers and membrane could vary greatly from one region to another. With the current scale of PEM fuel cell production, commercial-grade fuel cell components often display substantial deviations from their product specifications. Such component manufacturing issues hamper the overall effort toward improving commercial PEM fuel cell system reliability. Without adequate MEA quality control, it is difficnlt to interpret antopsy resnlts and to link apparent membrane/electrode problems of nsed MEAs to a particnlar failnre mechanism. Part of the problem is the lack of a nondestrnctive in-line MEA qnality control method to ensnre batch-to-batch consistency. 

In order to be used as UPS, flie fuel-ceU stack needs to be integrated to a complete system suitable for the application. The required components for fuel supply, controller, cooling, monitoring, etc. (Balance Of Plant, BOP) for critical infrastructures not only have to meet the typical requirements for a fuel cell, but also the application-specific requirements such as high reliability and low maintenance. 

If one desires to know the temperature distribution throughout the ceU, then an overall energy balance and transport equation must be utilized. This is often critical for identification of failure points that are geometry specific or perhaps in understanding phenomena that are due to the temperature gradient (e.g., phase-change-induced flow in fuel cells [4]). 

Especially for mass applications such as automotive, a full life cycle assessment (LCA) is absolutely critical. Since there are a lot of embedded resources such as noble metal catalysts and energy for manufacturing fuel cells, LCA very much depends on aspects such as recyclability and lifetime. For the operation period itself, cost, performance, and durability issues are important. But a complete picture must also consider aspects of specific applications including how they are connected in future energy scenarios. 

The terms E, and Xj are termed the critical parameters, and the Kjj are termed the critical specifications that are required to meet the functional requirements of the particular component under consideration. The term critical is of course an indication that the specification in question is one of the significant few specifications that will be tracked all the way from the voice of the customer down to the factory floor. In a complete PEM fuel cell system, there can be hundreds of specifications that will need to be tracked during the development of the system. Of these, perhaps a few dozen will remain critical even after the product has launched and is in production. 

---