For the cathode El, however, which has large agglomerates and a small inner specific area, we obtained 120 mV at 100 mA/cm2 for the polarization voltage. The electrode E2 has a high specific inner surface area but an agglomerate diameter which is rather large. This gives a polarization voltage of 50 mV at 100 mA/cm2.

»nomo Víou-io current density [mA/cm3]

»nomo Víou-io current density [mA/cm3]

Fig. 2: iR-free cathode polarization versus current density at various average agglomerate sizes

Cells with NiO/LiCoOj-DLCs, which are long term stable under pressure up to 5 bar, were operated at variable oxygen partial pressure. At realistic gas compositions, 650°C and 5 bar total pressure, a cell performance of 245 mW/cm1 was obtained. Fig. 3 shows the cell voltage as a function of current density at 1 and 5 bar pressure.

The catalytic activation of the inner surface of the LiCo02-layer makes it viable, to reduce the operating temperature without a serious performance penalty. Measurements on standard and activated DLC's have shown, that in the temperature range 550°C to 700°C the activation energy with respect to the charge transfer resistance can be reduced from 108 kj/mol to 60 kj/mol (see Fig.4).

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