Hole conductivity in the electrolyte of proton-conducting SOFC: Mathematical model and experimental investigation

Proton-conducting solid oxide fuel cell (SOFC) is promising for the intermediate and low temperature applications. The hole conductivity within the electrolyte has noticeable impact on the cell performance. In this article, a new model is proposed to evaluate the hole conductivity of the electrolyte directly. Single cells with different electrolyte thicknesses are fabricated to validate our model. The BaCe0.7Zr0.1Y0.2O3−δ electrolyte and Sm0.5Sr0.5CoO3−δ-Ce0.8Sm0.2O2−δ cathode is employed in our experiments. The predicted cell output capacities are in accord with both our experiments and the reported results, confirming that our proposed method is valid and effective. There are several distinct features of our model compared with previous reports: 1) Hole conductivity could be evaluated directly from the measured output voltages of the full cell, thus it simplifies the relevant experiment; 2) in order to make the cathode reaction model transferable among samples with diverse micro-structures, new parameters named TPB-specific exchange current density is proposed; and 3) for proton-conducting SOFC, an equivalent circuit model with the consideration of both electrolyte hole conductivity and various overpotentials is firstly proposed. Our model points out that the influence of the hole conductivity on the cell capacity could not be neglected in cases of relatively low output current, high temperature and thin membrane. Therefore the hole conductivity of the electrolyte must be taken into consideration in the related simulations.