Molten carbonate fuel cells cell components

Table 6.4. Contributions to life-cycle impacts from different components of a 1-m unit single molten carbonate fuel cell (based on data from Lunghi and Bove, 2003).

Petri, R.J. Benjamin, T.G. Molten carbonate fuel cell component design requirements. Proceedings of the 21st Intersociety Energy Conversion Engineering Conference, American Chemical Society Washington, DC, 1986 Vol. 2, 1156-1162. 

Fujita, Y. Nishimura, T. Urushibata, H. Sasaki, A. Degradation of the components in molten carbonate fuel cells with Li/Na electrolyte. Proceedings of the 4th Symposium on Molten Carbonate Fuel Cell Technology, PV. 97-4, Selman, J.R., Ed. Electrochemical Society Inc. Pennington, NJ, 1997 191-202. 

Paetsch, L. Pigeaud, A. Chamberlin, R. Maru, H. Development of Molten Carbonate Fuel Cell Components, Final Report to EPRI, Report No. AP 5789, Jul 1989. 

The work of Baur et al. (1916, 1921) must be recognized as the first work in the field of molten carbonate fuel cells. If is imporfanf fo note fhat the solid electrolyte (a mixture of monazite sand and other components including alkali metal carbonates), with which O. Davtyan worked in the 1930s, actually represented a carbonate melt immobilized in a solid skeleton of silicates. 

Several conversion technologies can be used to generate hydrogen from natural gas or diesel fuel. If we take methane as the main component of natural gas, the following chemical reactions are possible in an external reactor or internally in a solid oxide fuel ceU (SOFC) or an molten carbonate fuel cell (MCFC) ... 

Piewetz et al. [623] described a 32-kWei diesel fuel processor prototype designed for a molten carbonate fuel cell. It consisted of a hydrotreater unit operated at 45 bar and 380 °C for conversion of the 0.2 wt.% sulfur components present in the feed. A zinc oxide bed was positioned downstream, which adsorbed the hydrogen sulfide generated in the hydrotreater. The sulfur free feed then entered the reformer, which was operated at 25 bar and 480 °C. 

Chen W., Klein L.C., Huang C. Solution preparation of Li(Co,Fe)02 coatings for molten carbonate fuel cell components. J. Sol-Gel Sci. Technol. 2001 27 203-211... 

The molten carbonate electrolyte fuel cell (MCFC) has a history that can be traced back at least as far as the 1920s. It operates at temperatures around 650°C. The main problems with this type of cell relate to the degradation of the cell components over long periods. The MCFC does, however, show great promise for use in CHP systems, and this is discussed in detail in Section 7.4. 

A dense and electronically insulating layer of LiA102 is not suitable for providing corrosion resistance to the cell current collectors because these components must remain electrically conductive. The typical materials used for this application are 316 stainless steel and chromium plated stainless steels. However, materials with better corrosion resistance are required for longterm operation of MCFCs. Research is continuing to understand the corrosion processes of chromium in molten carbonate salts under both fuel gas and oxidizing gas environments (23,25) and to identify improved alloys (29) for MCFCs. Stainless steels such as Type 310 and 446 have demonstrated better corrosion resistance than Type 316 in corrosion tests (29). 

High temperature fuel cells (solid oxide and molten carbonates) efforts must be guided to materials development (catalysts, electrodes, electrolytes, plates, seals, etc), fuel cells components development and its manufacturing methods and fuel cells prototypes development. 

In recent decades, research has intensified to develop commercially viable fuel cells as a cleaner, more efficient source of energy, due to the global shortage of fossil fuels. The challenge is to achieve a cell lifetime suitable for transportation and stationary applications. Among the possible fuel cell types, it is generally believed that PEM fuel cells hold the most promise for these uses [10, 11], In order to improve fuel cell performance and lifetime, a suitable technique is needed to examine PEM fuel cell operation. EIS has also proven to be a powerful technique for studying the fundamental components and processes in fuel cells [12], and is now widely applied to the study of PEM fuel cells as well as direct methanol fuel cells (DMFCs), solid oxide fuel cell (SOFCs), and molten carbonate fuel cells (MCFCs). 

The two types of high temperature fuel cell are quite different from each other (Table 6). The molten carbonate fuel cell, which operates at 650°C, has a metal anode (nickel), a conducting oxide cathode (e.g. lithiated NiO) and a mixed Li2C03/K2C03 fused salt electrolyte. Sulphur attack of the anode, to form liquid nickel sulphide, is a severe problem and it is necessary to remove H2S from the fuel gas to <1 ppm or better. However, CO is not a poison. Other materials science problems include anode sintering and degradation, corrosion of cell components and evaporation of the electrolyte. Work continues on this fuel cell in U.S.A. and there is some optimism that the problem will be solved within 10 years. 

Table 6-1 Evolution of Cell Component Technology for Molten Carbonate Fuel Cells... 

An electrolyte is an essential component within fuel cells, used to facilitate the selective migration of ions between the electrodes. Fuel cells are typically classified according to the electrolytes used alkaline fuel cell (AFC), polymer electrolyte (or proton exchange membrane) fuel cell (PEMFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and solid oxide fuel cell (SOFC). Typical efficiencies, operating temperatures and output voltage for the various types of fuel cells are shown in Table 2.14. It should be noted that none of these fuel cells... 

Another fuel cell design is the molten carbonate fuel cell (MCFC) (Yuh, 1995), which operates in the temperature range 620-660°C with an efficiency of >50%. FuelCell Energy, Inc. (Danbury, CT) produces MCEC units. These units are designed as back-up generators for intermittent use. The operational lifetimes of fuel cell systems need to be extended. In order to do so, it is necessary to limit component corrosion. 

The high operating temperature of MCFCs provides the opportunity for achieving higher overall system efficiencies and greater flexibility in the use of available fuels compared with the low temperature types. Unfortunately, the higher temperatures also place severe demands on the corrosion stability and life of cell components, particularly in the aggressive environment of the molten carbonate electrolyte. 

Table 7.2 Evolution of cell component technology for molten carbonate fuel cells (Hirschenhofer et al 1998)...

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