Factors Influencing the Lifetime of SOFCs

The work on composite electrolytes is of great interest and may bring solid oxide fuel cells closer to commercialization. 

In Section 21.3, the fundamental problems arising in the development of planar solid oxide fuel cells have been listed sealing, corrosion of the bipolar plates, and the development of mechanical stresses in the numerous ceramic components found in such fuel cells. Solutions depend not only on the selection of suitable materials for the individual component parts of the fuel cells, but also on respecting certain principles of design and operation. 

This phenomenon is seen particularly in the highly disperse nickel used in the anodes of most solid oxide fuel cell variants. 

A serious problem arising during solid oxide fuel cell s operation is the interaction between the materials of electrodes and of the electrolyte, by diffusion of individual components from a given phase to a neighboring phase in contact with it. This interaction often gives rise to the formation of new phases or compounds having a low conductivity. 

Many of the factors influencing the solid oxide fuel cell s lifetime that are associated with ageing and degradation of these cells have been discussed in a review of Tu and Stimming (2004). 

In Section 8.2.1 we pointed out that a power plant with a battery of tubular SOFCs had been operated more or less successfiiUy for about 16,000 hours. Apart from the communication cited, very few data can be found in the literature as to the results of long-term testing of soUd-oxide fuel cells. Since this type of high-temperature fuel cell is intended primarily for large stationary power plants and thus has large investment needs, information as to potential lifetimes and reasons for gradual performance degradation or possible cases of sudden failure are extremely important. 

Thermal shocks have a highly negative effect on lifetime. These are sudden temperature changes in individual segments of a fuel cell. The development of considerable temperature gradients within given segments is also detrimental. 

Another important aspect is that of thermal management during startup and shutdown of a power plant. This problem has been discussed in detail by Apfel et al. (2006). 

Various processes taking place in the electrodes and in the electrolyte of a fuel cell also influence the lifetime of SOFCs, in addition to the factors already mentioned. As in other types of fuel cells, the active working surface area of highly disperse metal catalysts has a tendency to shrink gradually with time. This decrease leads to a gradual increase in polarization of the corresponding electrode. 

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FACTORS INFLUENCING THE LIFETIME OF SOFCs 21.7 LOW-TEMPERATURE SOFCs (LT-SOFC)... 

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