Gas diffusion hindrances on Ni cermet anode in contact with Zr0.84Y0.16O1.92 solid electrolyte

Abstract

The electrochemical behavior of Ni cermet electrode with CeO2 − x additive in contact with YSZ electrode was studied by means of impedance spectroscopy in H2, H2O, CO2, CO, He, and Ar gas media of various composition within the temperature range of 700 to 950°C. Near the equilibrium potential, the electrochemical impedance spectra of the studied electrodes indicate to three stages of electrode reaction. The polarization conductivity of the low-frequency stage of electrode reaction (σlf) is characterized with the following regularities: (a) temperature dependence of σlf has a positive slope in Arrhenius coordinates; (b) σlf increases upon replacement of gas mixture with lower mutual diffusion coefficient by mixture with higher mutual diffusion coefficient, while polarization conductivity values of other stages remain practically invariable; (c) concentration relationships of 1/σlfrecorded for constant activity of oxygen in the gas phase are linear in the 1/σlf vs. 1/P CO 2 (P CO) coordinates; (d) no low-frequency stage of the electrode reaction is observed upon electrochemical inflow (outflow) of the gas reagents (reaction products) to (from) the test electrodes (current passing through closely pressed specimens and central specimen impedance measurement); and (e) no change in the gas flow rate affects σlf value. The observed regularities were explained by assuming the gas diffusion nature of the low-frequency stage of the electrode reaction. The gas diffusion layer thickness was estimated.