650

Pressure 7ata Max. temp. G75"C

Current density 150mA/cm2

Fuel gas H2/C02/H20=54.4/13.6/32 Uf=60!i

Oxidant Air/C0,=70/30

Figure 4 shows history of the stack performance. Initial stack performance such as pressure gain and fuel utilization characteristics, was measured before 500 h. Since then, the stack has been operated under constant condition. Operation pressure was 7 ata. Cathode gas composition was Air/C02=80/ 20 since high C02 partial pressure accelerates shorting by NiO cathode dissolution. Both Li/K and Li/Na cells showed stable performance until 1400 h. However. Li/K mean cell voltages began to drop after 1400 h. Shorting by NiO cathode dissolution is assumed to be a cause for dropping of voltage. Anode inlet and outlet gas compositions have been usually analyzed by the gas chromatography in parallel with the operation. Fuel consumption by cell reaction . combustion and methanation was calculated with mass balance between anode inlet and outlet gas compositions. Shorting current density was

OCell voltage (Li/K) □ ir compensated (Li/K) • Cell voltage (Li/Na) ■ ir compensated (Li/Na)

0.2 0.4 0.6 0.8 : 1 Parameter A in Eq.1 Fig. 3 Relationship between cell voltage and parameter A

0 0

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