N

possibility of CeYSZ particles in the cermet "j= - 2 0

electrode producing the electrochemically active sites as Ni in the cermet plays a roles in the same way. The cell (c) in Figure 2 had the Ni-CeYSZ cermet electrode, whose rest of component materials were same as those of cell (b). Therefore, the improvement seen in the V-I characteristic from cell (b) to cell (c) in Figure 2 was considered to be the result of the increased active sites.

0 5 1015 20 25303540 Re(Z)

Figure 4

Typical AC impcdance spectrum for a Ni/CeYSZ electrode on a YSZ electrolyte. Closed symbols indicates a fit by the equivalent circuit of Figure 5.

0 5 1015 20 25303540 Re(Z)

Figure 4

Typical AC impcdance spectrum for a Ni/CeYSZ electrode on a YSZ electrolyte. Closed symbols indicates a fit by the equivalent circuit of Figure 5.

To investigate the effect of Ce02 addition to the Ni-YSZ cermet, electrode characteristics were measured by an AC impedance method. A typical AC impedance spectrum of the Ni-CeYSZ cermet electrode is shown in Figure 4. The closed symbol represents calculated values by the equivalent circuit with a finite length diffusion impedance5' shown in Figure 5. The electrode interface conductivity (a.)'1 of Ni-CeYSZ, calculated from the equivalent circuit, is compared in Figure 6 with that of the Ni-YSZ electrode. This clearly indicates that the interface conductivity increased by the addition of Ce02. The increase in <Je supports the postulation that the Ni-CeYSZ cermet anode has more electrochemically active sites than does the Ni-YSZ cermet anode.

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