Polymer electrolyte fuel cells considerations

In recent years, the preparation and properties of Pt-Ru/C electrocatalysts for polymer electrolyte fuel cell applications have received considerable attention [94-97]. 

Although the low operating temperature of the unit is usually seen as an advantage, in some instances temperatures as low as 80°C are not high enough to perform useful cogeneration. Furthermore, in order to achieve the most effective operation of the unit, the electrolyte must be saturated with water. Control of the moisture of the anode and cathode streams therefore becomes an important consideration. The PEM fuel cell is also sometimes referred to as a polymer electrolyte fuel cell (PEFC). 

Obviously the increasing importance of solid electrolytes as employed in solid oxide or polymer membrane fuel cells calls for experimental methods adapted specifically to the needs of these experimental setups, which are considerably different from those employing liquid electrolyte solutions. The number of experimental methods beyond classical electrochemical ones adapted specifically to these requirements was fairly low when preparing this chapter. In most cases standard surface analytical or solid state analytical techniques were employed for an introductory overview see [3]. Nevertheless, these electrochemical systems are not taken into... 

In this section, recent advances in the field of polymer electrolyte direct methanol fuel cells, i.e., PEFCs based on direct anodic oxidation of methanol are discussed. A schematic of such a ceU is shown in Fig. 48, together with the processes that take place in the cell. The DMFC has many facets, electrocatalysis materials and components which deserve a detailed treatment. The discussion here will be confined, however, to the very significant performance enhancement demostrated recently with polymer electrolyte DMFCs, and, as a result, to possible consideration of DMFCs as a nearer term technology. 

The Chapter by R. Adzic, N. Marinkovic and M. Vukmirovic provides a lucid and authoritative treatment of the electrochemistry and electrocatalysis of Ruthenium, a key element for the development of efficient electrodes for polymer electrolyte (PEM) fuel cells. Starting from fundamental surface science studies and interfacial considerations, this up-to-date review by some of the pioneers in this field, provides a deep insight in the complex catalytic-electrocatalytic phenomena occurring at the interfaces of PEM fuel cell electrodes and a comprehensive treatment of recent developments in this extremely important field. 

Exciting research is underway to improve the performance and longevity of batteries, fuel cells, and solar cells. Much of this research is directed at enhancing the chemistry in these systems through the use of polymer electrolytes, nanoparticle catalysts, and various membrane supports. Additionally, considerable effort is being put into the construction of three-dimensional microbatteries, see also Electrochemistry AIaterials Science Solar Cells. 

In June 2001 we initiated this project to explore the possibilities of decreasing the Pt loading in Pt-Ru catalysts for H2/CO oxidation in the polymer electrolyte membrane fuel cells (PEMFCs). We have demonstrated a new method for the preparation of the Pt-Ru catalysts involving spontaneous deposition of Pt on Ru nanoparticles that we explored first with single crystal Ru surfaces. The resulting catalysts have a high CO tolerance with considerably lower Pt loading than the commercial catalysts. 

In last few years there has been considerable amount of activity in using ink-jet technology for printing different components of a fuel cell particularly those for polymer electrolyte membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC). The various components reported to have been printed using ink-jet are as follows ... 

Considerable changes are needed in the anodic part of the membrane-electrode assemblies in order to accommodate the first two of the above-mentioned points. Instead of the porous gas diffusion layer that in polymer electrolyte membrane fuel cells ensures a uniform distribution of hydrogen across the surface, a gas-liquid diffusion layer that contains a set of hydrophilic as well as a set of hydrophobic pores is needed here. Through the hydrophilic pores, this layer must secure the unobstructed access of the aqueous methanol solution to the reaction zone and its uniform distribution. Through the hydrophobic pores, this layer must secure the unobstructed elimination of carbon dioxide, as the gaseous reaction product, from the reaction zone. Analogous changes must be made in the catalytically active anode layer of the membrane-electrode assemblies, where the gas is actually formed, and must be removed toward the gas-liquid diffusion layer. 

It is well known today that perhaps the most dramatic application of the fuel cell—an electrochemical device that may be based in the future upon the oxidation of aliphatic hydrocarbons— was in the Gemini Space Mission. In this application, the cell was based upon the use of a solid polymer electrolyte —a cation-exchange membrane in its acid form—but with hydrogen and oxygen as the fuels rather than an aliphatic hydrocarbon. Considerable research and development preceded and supported these successful missions and the units demonstrated that indeed the H2/O2 fuel cell was capable of extended performance at relatively high current densities—2l capability of fundamental importance in commercial applications. 

Therefore, the requirement for active management of the PEM water content adds considerable system cost, complexity, and unreliability. Because of this, there is considerable research under way addressing the development of alternative classes of acid-based polymer electrolytes for fuel cells. There are excellent reviews of the progress being made in the development of these alternative polymer electrolytes [22]. 

This chapter discusses the subject of fuel cells how they work and how they are designed and integrated into a collection of subsystems for application in a variety of applications. Particular focus is placed upon systems utilizing polymer electrolyte membranes, and how the properties of the membrane dictate the system design considerations. 

In recent years, fuel cells have attracted considerable attention due to their high energy efficiency with zero emissions [1]. Electrocatalysts are some of the key materials used in low-temperature fuel cells such as the polymer electrolyte membrane fuel cell (PEMFC) and the direct methanol fuel cell (DMFC). Creating high-performance catalysts is widely recognized as a key step for the further development and commercialization of low-temperature fuel cells. 

Whiteley, M. et al. 2013a Enhanced fault tree analysis and modelling considerations of a polymer electrolyte membrane fuel cell, in Proceedings of the European Safety and Reliability Conference, ESREL. CRC Press, 29/09/2013. 603. 

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