Zirconia electrolyte stack

Figure 6.18 Schematic diagram of a fuel cell stack using a stabilized zirconia electrolyte.

Scandia-stabilized zirconia electrolyte with standard SOFC electrodes is used to construct the cells. Stacks are constructed using stainless steel interconnects. The surfaces of the stainless steel are treated to provide an electrically conductive scale with low-scale growth rate. The performance characteristics of a single cell (2.5 cm active area) and a 25-cell stack (active area of 64 cm per cell) are shown in hgure 3.5 and hgure 3.6. The performance stability of the stack is shown in hgure 3.7. 

FIGURE 3.6 Stack performance using Sc-doped zirconia electrolyte and metal interconnects. 

Recently, the Swiss company Sulzer Hexis AG has developed the concept of an SOFC for small-scale domestic application to provide heating on demand and to cover peak power requirements. This so-called Hexis (Heat Exchanger Integrated Stack) cell consists of circular zirconia electrolyte disks of about 12 cm diameter that carry the anode and cathode (Figure 7.38). The individual cells are... 

For the purposes of review. Figure 1 illustrates the basic function of the cathode in a solid oxide fuel cell. Whether acting alone or as part of a stack of cells, each cell consist of a free-standing or supported membrane of an oxygen-ion-conducting electrolyte, often yttria-stabilized zirconia (YSZ). Oxygen, which is fed (usually as air) to one side of the membrane, is reduced by the cathode to oxygen ions via the overall half-cell reaction... 

The stack electrolytes are scandia-stabilised zirconia, about 140 (im thick. The air-side electrodes (anode in the electrolysis mode) are a strontium-doped manganite. The electrodes are graded, with an inner layer of manganite/zirconia ( 13 pm) immediately adjacent to the electrolyte, a middle layer of pure manganite ( 18 pm), and an outer bond layer of cobaltite. The steam/hydrogen electrodes (cathode in the electrolysis mode) are also graded, with a nickel-zirconia cermet layer ( 13 pm) immediately adjacent to the electrolyte and a pure nickel outer layer ( 10 pm). 

The major components of an individual SOFC cell include the electrolyte, the cathode, and the anode. Fuel cell stacks contain an electrical interconnect, which links individual cells together in series or parallel. The electrolyte is made from a ceramic such as yttria-stabilized zirconia (YSZ) and functions as a conductor of oxide ions. Oxygen atoms are reduced into oxide ions on the porous cathode surface by electrons, and then flow through the ceramic electrolyte to the fuel-rich porous anode where the oxide ions react with fuel (hydrogen), giving up electrons. The interconnect serves to conduct the electrons through an external circuit. 

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