En: theoretical cell voltage, AEnl: Nernst loss, AE^t): Cell voltage reduction by self shorting, R„(t)+Rc(t): Non-ohmic polarization, RoIrai(t) : Ohmic cell resistance.

The reduction of OCV was corresponded to the self shorting by the deposition of nickel. AE^t) was estimated from the profile of OCV with time. Ohmic resistance was estimated by the profile cell resistance with time. We have three different degradation rates, a, is the observed degradation rate, a, is corrected by subtracting AENi0(t). a3 is corrected by subtracting AENi0(t) and (RoiJt) -Rchr/°))-

E,(t,I=150mA/cmi)=E0-AEn.I-AENi0(t)-(Ra(t)+Rc(t)+Rohm(t))I =Elo(t=0,1=150mA/cnr)-ct,t-------------(1)

E2(t,I= 150mA/cm2)=E0-AElll-(Ra(t)+Rc(t)+Rohm(t))I =E2O(t=0,1=150mA/cm2)-a,t-----------(2)

E3(U=150mA/cm2)=E0-AEal.-(Ro(t)+Rc(t)+Rohm(0))I =E3O(t=0, I=150mA/cm2)-a3t-----------(3)

The degradation behaviors of tested MCFCs at operation time were different. We considered three steps for long operation. The degradation rate at third step were higher than those at other steps. The large degradation at third step was caused by the short circuit and the increasing cell resistance. We guess that the difference of34000-hour-operation MCFC and 40000-hour-operation MCFC was due to the different pore distribution of matrix . It came from the different fabrication process of matrix.

Table 1. Degradation rate of 34000-hour Table 2. Degradation rate of40000-hour -operation_ -operation._

1st step 2nd step 3rd step
0 0

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