Fuel Cell Description

The 30-year technological story of flexible graphite, and example modern flow plate/fuel cell descriptions, are given in four Graftech patents (Mercuri, 2001a, b 2002a, b). 

PEM Fuel Cell Description 1.2.1 Fuel Cell Reactions... 

Catalyst Layer Morphology The microstructure of the catalyst has a strong effect on the overall effectiveness of the catalyst. From the generic fuel cell description of Chapter 2, the catalyst structure is highly three dimensional, and the potential reaction locations are limited to those with immediate access to ionic and electronic conductors, catalyst, and reactant gas. Maximization of this triple phase boundary area will reduce the activatiou polarization losses for a given current density. A catalyst layer with very low triple-phase boundary area density will have reduced number of available reaction sites and reduced performance. 

A brief description of various electrolyte cells of interest follows. A detailed description of these fuel cells may be found in References (1) and (2). 

A logical first step in understanding the operation of a fuel cell is to define its ideal performance. Once the ideal performance is determined, losses can be calculated and then deducted from the ideal performance to describe the actual operation. Section 2.1.1 is a description of the thermodynamics that characterize ideal performance. Actual performance is addressed in Section 2.1.2. Section 2.1.3 provides a lead-in to the development of equations in Section 3 through Section 8 that quantify the actual cell performance as a function of operating conditions for PEM, PAFC, AFC, ITSOFC, MCFC, and SOFC, respectively. 

This coincides with ongoing research to increase power density, improve water management, operate at ambient conditions, tolerate reformed fuel, and extend stack life. In the descriptions that follow, Ballard Power Systems fuel cells are considered representative of the state-of-the-art. 

A flow diagram for a natural gas fueled, 4 MW class, solid state fuel cell power cycle is presented in Figure 9-11. A brief process description is given below, followed by a performance summary. Selected state point values are presented in Table 9-16. 

Below is a listing and brief description of organizations involved in the development of codes and standards pertaining to fuel cell technology. 

With the increased computational power of today s computers, more detailed simulations are possible. Thus, complex equations such as the Navier—Stokes equation can be solved in multiple dimensions, yielding accurate descriptions of such phenomena as heat and mass transfer and fluid and two-phase flow throughout the fuel cell. The type of models that do this analysis are based on a finite-element framework and are termed CFD models. CFD models are widely available through commercial packages, some of which include an electrochemistry module. As mentioned above, almost all of the CFD models are based on the Bernardi and Verbrugge model. That is to say that the incorporated electrochemical effects stem from their equations, such as their kinetic source terms in the catalyst layers and the use of Schlogl s equation for water transport in the membrane. 

A schematic of a typical fuel-cell catalyst layer is shown in Figure 9, where the electrochemical reactions occur at the two-phase interface between the electrocatalyst (in the electronically conducting phase) and the electrolyte (i.e., membrane). Although a three-phase interface between gas, electrolyte, and electrocatalyst has been proposed as the reaction site, it is now not believed to be as plausible as the two-phase interface, with the gas species dissolved in the electrolyte. This idea is backed up by various experimental evidence, such as microscopy, and a detailed description is beyond the scope of this review. Experimental evidence also supports the picture in Figure 9 of an agglomerate-type structure where the electrocatalyst is supported on a carbon clump and is covered by a thin layer of membrane. Sometimes a layer of liquid water is assumed to exist on top of the membrane layer, and this is discussed in section 4.4.6. Figure 9 is an idealized picture, and... 

In that review ( 1), a description of practically all devices built and tested in the U.S. and Europe was presented. In this paper, the emphasis will be placed on the fundamental principles as well as the different factors that limit the fuel cell we will discuss the most recent development of stationary power sources. 

A second workshop, Catalysis for Sustainable Energy Production , was held in Sesto Fiorentino (Florence, Italy) from 29 November to 1 December 2006. The structure and approach of this workshop were similar to those of the first, but the focus was on (i) fuel cells, (ii) hydrogen and methane storage and (iii) H2 production from old to new processes, including those using renewable energy sources. The present book is based on this second workshop and reports a series of invited contributions which provide both the state-of-the-art and frontier research in the field. Many contributions are from industry, but authors were also asked to focus their description on the identification of priority topics and problems. The active discussions during the workshop are reflected in the various chapters of this book. 

This section delineates the work reported on fuel cells. It starts with a descriptive overview of fuel cell technologies, including a synopsis of each of the major fuel cell types. It then provides a review of lEA government work as it relates to each fuel cell type. The section also includes a summary of general work conducted on basic fuel cell R D and a review of fuel cell demonstrations for both transportation and stationary applications. 

This section provides a brief description of the various, "leading" fuel cell technologies currently under development. 

Swiss chemist Christian Schonbein (1799-1868) publishes the first description of a fuel cell. 

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