Deconvoluting electrode polarization resistances underestimated due to electronic leakage in proton ceramic cells

Proton ceramic cells lose faradaic efficiency through electronic leakage in the electrolyte that electrochemical impedance spectroscopy (EIS) cannot resolve directly. Proton conducting electrolytes such as BaZr 0.7 Ce 0.2 Y 0.1 O 3−δ (BZCY721) exhibit non-negligible p-type electronic conductivity that short-circuits the electrode polarization processes, causing systematic underestimation of their impedances. Here, we apply a correction procedure in which the electronic resistance is placed in parallel with the faradaic resistances in equivalent-circuit analysis, thus yielding true electrode polarization resistances. The procedure is applied to a symmetric cell comprising porous Ba 0.95 La 0.05 Fe 0.7 Ni 0.2 Zn 0.1 O 3−δ (BLFNZ) electrodes on BZCY721 and the ionic and electronic transport numbers are obtained by fitting the measured total electrolyte conductivity based on defect chemistry and transport equations. Accounting for the electronic short-circuit markedly alters the deconvoluted electrode polarization resistances, activation energies, pre-exponential factors, and reaction orders. The apparent electrode polarization resistance is underestimated by approximately one order of magnitude at 600°C, and the activation energy is reduced from the apparent 1.3 eV to 0.8 eV. The corrected charge-transfer and mass-transfer conductances are consistent with proton transfer ( p O 2 0 and p H 2 O 1 / 2 dependences) and oxygen exchange ( p O 2 1 / 4 and p H 2 O 0 dependences), respectively. The impact of the electronic leakage is quantified by equivalent circuit analysis of the electronic and faradaic conductances.