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2.1 Modelling of SOFCThe SOFC model used in this investigation is based on the model developed in Bang-Møller and Rokni (2010), which were calibrated against experimental for planar SOFCtype.E E E E E E(1)FCNernstactohmwhere E Nernst , E act , E ohm , E conc , E offset are the Nernst ideal reversible voltage,activation polarization, ohmic polarization, concentration polarization and the offsetpolarization respectively. The activation polarization can be evaluated from Butler –Volmer equation (see Keegan et al. 2002). This was isolated from other polarization todetermine the charge transfer coefficients as well as exchange current density from theexperiment data and via curve fitting technique. It followed,E E Econc2RT sinhF offset i in 2i0,a sinh i i 2i11nact act,c act,a(2)0,cwhere R, T, F and i d were the universal gas constant, operating temperature, Faradaysconstant and current density respectively. i n was an internal current density added to theactual current density to account for the mixed potential caused by fuel crossover andelectrons passing through the electrolyte. This value was adjusted when calibrating theelectrochemical model. The anodic and cathodic current densities were calculated fromii0,a0,c pH2 a p p c pO2c,totapHp0.252Oa Eexp RT Eexp RTact,cact,a, (3)where E act,a = E act,c = 1.2x10 5 J/mol. The constants a and c were calibrated againstexperimental data and found to be 11x10 9 mA/cm 2 and 3.5x10 8 mA/cm 2 , respectively.The ohmic polarization depends on the electrical conductivity of the electrodes as well asthe ionic conductivity of the electrolyte which could be described astel E ( i i(4)ohm n)ee,0 Eact,ee exp (5)T RT where the electrolyte thickness t el = 10 m is assumed. The constant e0 is assumed to be3.6x10 5 S/cm.The concentration polarization is dominant at high current densities for anode-supportedSOFCs, wherein insufficient amounts of reactants are transported to the electrodes andthe voltage is then reduced significantly. Neglecting the cathode contribution, it could bemodeled asRT p H 2i in i inE concln 1ln 1 , (6)neF pH2Oias iaswhere n e = 2, since it was assumed that all CH 4 and CO are converted to H 2 before theelectrochemical reactions take place. In the above equations p H2 and p H2O are the partialRisø International Energy Conference 2011 Proceedings Page 290