Of the cells available, solid oxide fuel cells
(SOFCs) appear to be nearest to commercial use for
large-scale electricity generation. A variety of
designs are being explored, including planar and
tubular geometries (Figure 9.13). In all cases, single
cells are linked to give a fuel-cell stack by an interconnecting material. The electrolyte in these cells is
the oxygen ion conductor yttria-stabilised zirconia
(YSZ). The defect chemistry of this material is similar to calcia-stabilised zirconia (Section 3.4.5).
Zirconia is doped with Y2O3(yttria) to form a phase
with Y3+ substituted for Zr4+
As the dopant ions
have a lower charge than the Zr4+ ions, the crystal
compensates by introducing anion vacancies, resulting in a high oxygen ion diffusion coefficient.