Future Development of PEMFCs

Yet these uses are not on a mass scale, and the commercial success, deriving from the production of such power plants, is still very limited. A wider use of this kind of fuel cells can only be expected, when they have conquered two new areas of application, light electric vehicles, and portable electronic equipment. For success in this direction, a number of important and rather complex problems must be solved first  

As power supply for a variety of portable devices is one of the more important future applications of polymer electrolyte membrane fuel cells, great efforts are made at present to reduce the dimensions and weight, and to even miniaturize both the fuel-cell stack and all auxiliary equipment needed for a power plant. 

There are a few different aspects to the concept of lifetime. They cover values of the following parameters of a power plant with fuel cells that have either been attained or are guaranteed or expected  

the time of smooth, uninterrupted operation in a given operating mode  

the number of (admissible) temperature cycles between ambient and operating temperatures and back. 

UTC Power (South Windsor, Connectient), a United Technologies Company, produces power units with PEMFCs for different mihtary and civil applications. In 2002, regular electric bus service using fuel cell batteries developed by this company was started. The Pure Cell model 200M Power Solution power plant delivers 200 k W of electric power and about 900 Btu/h (about 950 kJ/h) of thermal power (www.utcpower.com). 

Plug Power (Latham, New York), founded in 1997, has delivered since 2000 emergency power plants on the basis of PEMFC batteries providing uninterruptible power supply for hospitals and other vitally important objects in cases of sudden loss of grid power (www.plugpower.com). 

At present, in addition to the United States, PEMFCs and power plants based on them have been developed in many other countries, including China, France, Germany, South Korea, and the United Kingdom. Most of the power plants delivered in 2006 (about 60%) were for power supply to portable equipment. A secondary use (about 26%) was as small stationary power plants for an uninterruptible power supply. 

Approximately 75% of the work on PEMFCs is conducted in indushial organizations, the remaining 25% in academic and government organizations. This proves that the initial research and engineering stage has been completed, and commercial development of these fuel cells is under way (see the review by Crawley, 2006). A detailed analysis of the many ways used to make PEMFCs may be found in the review of Mehta and Cooper (2003). 

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The editors beheve that this book is the first book exclusively dedicated on fuel cell membranes in which the experts of the field are brought together to review the development of polymeric membranes for PEFC in all their aspects. The book was written for engineers, scientists, professors, graduate students as well as general readers in universities, research institutions and industry who are engaged in R D of synthetic polymeric membranes for PEMFC. It is therefore the editors wish to contribute to the further development of PEMFC by showing the future directions in its R D. 

In view of the significant modeling activities and number of active groups worldwide, it is useful to assess the current status to ensure future developments will address PEMFC areas of major concern. This is especially important considering that PEMFCs are at a critical juncture. Large capital amounts have already been spent during the last ten years with even larger sums likely... 

Development of high-temperature proton exchange membranes and catalysts for HT-PEMFCs are equally important in terms of the long-term sustainability of fuel cell technology and commercialization. Based on a review of the literature as well as our understanding, we would like to suggest several future research topics for high-temperature catalyst development ... 

Electro-catalyst supports play a vital role in ascertaining the performance, durability, and cost of PEMFC and DMFC systems. A myriad of nano-structured materials including carbon nanostructures, metal oxides, conducting polymers, transition metals nitrides and carbides, and many hybrid conjugates, have been exhaustively researched to improve the existing support and also to develop novel PEMFC/DMFC catalyst support. One of the main challenges in the immediate future is to develop new catalyst supports that improve the durability of the catalyst layer and, in a best-case scenario, also impact the electronic properties of the active phase to leapfrog to improve catalyst kinetics. 

There exist a variety of fuel cells. For practical reasons, fuel cells are classified by the type of electrolyte employed. The following names and abbreviations are frequently used in publications alkaline fuel cells (AFC), molten carbonate fuel cells (MCFC), phosphoric acid fuel cells (PAFC), solid oxide fuel cells (SOFC), and proton exchange membrane fuel cells (PEMFC). Among different types of fuel cells under development today, the PEMFC, also called polymer electrolyte membrane fuel cells (PEFC), is considered as a potential future power source due to its unique characteristics [1-3]. The PEMFC consists of an anode where hydrogen oxidation takes place, a cathode where oxygen reduction occurs, and an electrolyte membrane that permits the transfer of protons from anode to cathode. PEMFC operates at low temperature that allows rapid start-up. Furthermore, with the absence of corrosive cell constituents, the use of the exotic materials required in other fuel cell types is not required [4]. 

Fig. 15.25 Pathways for future electrocatalyst development for automotive PEMFCs. (a) Thick films or bulk single crystal and polycrystalline catalysts that are ideal for fundamental studies on surface structure and mechanisms these materials need to be modified into (c) and (d) to be applicable to fuel cells, (b) Typical commercial nanoparticles (2-4 nm) on a high-surface-area carbon support used in fuel cells at this time (c) Thin continuous films of catalyst on a support such as carbon nanotubes that may provide a physical porous structure for mass transport in a fuel cell (d) Core-shell catalysts where only the shell eonsists of precious metals and are supported on a typical high-surface-area support [72, 77, 89]...

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