Loss of Gibbs Energy Using Sm-Doped Ceria Electrolytes in SOFCs Considering Local Equilibrium while Ion Hopping

ABSTRACT

Using Sm-doped Ceria electrolytes (SDC) in SOFCs (solid oxide fuel cell), the open circuit voltage (OCV) becomes lower than the Nernst voltage (Vth), which is obtained using Yttria-stabilized Zirconia (YSZ) electrolytes. Classically, OCV is calculated with Wagner’s equation. However, experimental verification of leakage currents using SDC electrolytes is necessary, both qualitatively and quantitatively. Furthermore, there are limitations in Wagner’s equation using SDC electrolytes, from the limits of linear transport theory. Consequently, the voltage loss in OCV cannot be explained by the conventional transport equations with leakage currents, in which the system as being close to equilibrium. In this report, the constant voltage loss without leakage currents due to mixed ionic and electronic conducting (MIEC) dense anode is proposed, considering the local equilibrium to deal with the transition state while ion hopping. Thus, the effective Gibbs energy is smaller than the theoretical Gibbs energy.

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