Temperature SOFC current

Unlike molten carbonates, solid oxides use a hard ceramic electrolyte instead of a liquid. That means the fuel cell can be cast into a variety of useful shapes, such as tubes. With higher temperatures, sofcs may be able to cogenerate steam at temperatures as high as i,ooo°f. The Siemens Westinghouse Power Corporation has built the first advanced hybrid system, which combines a gas turbine with a tubular sofc. As of 2003, the 220 kW hybrid system has operated in California for more than 2,000 hours with a respectable 53 percent efficiency, comparable to current combined cycle gas turbines. The ultimate goal is an efficiency of 70 percent or more. 

Solid oxide fuel cells (SOFCs) are one of the most efficient energy conversion devices [1]. The main demand in the current SOFC development is lowering operation temperature to the range of 600-800 C - intermediate temperature SOFC (IT-SOFC). In order to lower operational temperature and increase or at least sustain performance comparable to that at high temperature SOFCs, it is necessary to decrease the resistance of the electrolyte and lower the overpotential of the electrodes. One of the ways to achieve this goal is to decrease the thickness of the electrolyte and optimize the structure of the electrodes. 

Scientists are currently exploring the potential for developing lower-temperature SOFCs operating at or below 800°C ( 1,500°F) that have fewer durability problems and cost less. Lower-temperature SOFCs produce less electrical power, however, and stack materials that will function in this lower temperature range have not been identified. 

Kulikovsky, A.A. (2010) Temperature and current distribution along the air channel in planar SOFC stack model and asymptotic solution. J. Fuel Cell Sci. Technol, 7 (1), 011015. 

Anodes perform electrooxidation of fuel by catalyzing the reaction and facilitating fuel access and product removal [1]. These require sufficient reaction sites for the fuel oxidation and electronic conductivity to transfer electrons from the oxidant to the cell components, i.e., electrol34e and current collectors. In high-temperature SOFCs, porous cermets, made from a percolating metal phase and... 

The model is used to study the effect of a resistive spot on temperature and current distribution in a 15-cell fragment of a planar SOFC stack (Figure 5.21). Two variants have been calculated. In the base case, the stack contained no spots this variant provides the reference undisturbed distribution of stack temperature Tsase-... 

Fuel cells were invented more than 150 years ago, but their commercialization has been very slow. To date, they have been used primarily in space vehicles, but these systems are quite costly and not suitable for commercial applications. In the last decade, however, there has been a dramatic increase in research, and it is now clear that fuel cells will enter the commercial marketplace in the not too distant future. Currently, most attention is focused on two types of fuel cells, polymer-electrolyte membrane (PEM) fuel cells and solid-oxide electrolyte fuel cells (SOFCs) (Carrette et al., 2000 Minh 1993). PEM systems use a proton-conducting polymer as the electrolyte and operate at low temperatures SOFCs use an oxygen ion-conducting ceramic membrane as the electrolyte and operate at temperatures of 700 to 1,000°C. 

It is generally considered that the cathodes for intermediate-temperature SOFCs should be electrochemically more active than those cathodes in the first generation, namely, LSM. When LSF, LSC, or LSCF is used as cathode, an interlayer made of doped ceria becomes inevitable to avoid chemical reactions between cathode and YSZ. In addition, such cathodes should be also protected against Cr vapors. This approach gives rise to a complicated layer structure across the electrolyte to current collector and makes it difficult to fabricate such complicated layers. For example, the following points are important ... 

Even for the intermediate-temperature SOFCs, Ni is the best anode as far as the current technological status is concerned. Although a number of investigations have been made on oxide anodes, nickel cermet (ceramic-metal) anodes exhibit... 

The final piece of the polarization curve to be modeled is the departure from the expected OCR given by the Nemst equation. For low-temperature PEFCs, the OCV is predicted to be around 1.2 V, but in practice, only about 1.0 V is observed. For a high-temperature SOFC, however, the actual OCV can be very close to the theoretical OCV. For the PEFC, the 0.2 V represents an incredibly significant efficiency loss before any useful current is even drawn. The departure from the theoretical OCV is typically a result of two phenomena ... 

The departure from Nernst OCV is a result of reactant crossover through the electrode and mixed reaction potential, or electrical shorts from mixed electrolyte conductivity. For most fuel cell systems, the major concern is reactant crossover, although high-temperature SOFC systems suffer from some electrical conductivity in the electrolyte. For the mass crossover case, the effect can be modeled by inclusion of the crossover current density with the fuel cell current density activation overpotential at the electrode with the mixed potential reaction. 

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