Fuel Cell Technology: Reaching Towards Commercialization

4.3: Modeling of Solid Oxide Fuel Cells

4.3 Modeling of Solid Oxide Fuel Cells

A solid oxide fuel cell (SOFC) consists of three main components: a porous cathode (or air electrode), a porous anode (or fuel electrode), and an ion-conducting ceramic membrane, as shown in Figure 4.26. The operation temperature of SOFCs are high, typically between 700 C and 1000 C, to ensure sufficient ionic conductivity in the membrane and to promote electrochemical reactions. Similar to the PEM fuel cells, the advantages of the SOFCs include high-efficiency, high energy density, and low pollution. Furthermore, a major constraint of the PEM fuel cells, i.e., the requirement of hydrogen fuel, is relaxed in SOFCs. Although hydrogen is taken as a future alternative to the depleting fossil fuel, a number of issues related to hydrogen generation and storage limit the large-scale usage of hydrogen. About 96% of hydrogen is currently obtained by reforming hydrocarbons, and 20 to 30 percent of the chemical energy is wasted during the process [164]. Since the energy density of hydrogen gas is low compared to that of hydrocarbon liquid, hydrogen storage may be difficult and expensive.

Figure 4.26: Schematic of a solid oxide fuel cell (redrawn from [178])

Two types of geometries are commonly used for SOFCs, namely, tubular and planar configurations as shown in Figures 4.27(a) and 4.27(b), respectively. Some model power plants manufactured by Siemens-Westinghouse adopt the tubular design, which has demonstrated high efficiency and long term stability (3). However, two technical problems are associated with the tubular design, namely, high fabrication...


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