Microstructural and electrochemical properties of Ni-impregnated GDC10 and 8YSZ freeze tape cast scaffolds as fuel electrodes for solid oxide cells

Ni-impregnated Gd0.1Ce0.9O2 and Y0.08Zr0.92O2 fuel electrodes for solid oxide cells are manufactured by the combination of the freeze tape casting and infiltration techniques. Their morphological properties are investigated by scanning electron microscope and X-Ray microtomography while their electrochemical performance is evaluated in symmetrical Y0.08Zr0.92O2-supported button cells by electrochemical impedance spectroscopy. The microstructural analysis of the manufactured scaffolds highlights the characteristic anisotropy of porosity provided by the freeze tape casting method. The average tortuosity factor across the out of plane direction has been calculated equal to 1.38, being considerably lower than the average values of the other components, (τx = 10.2) and (τy = 6.87). The contribution provided by gas diffusion to the overall polarization resistance of the freeze tape cast electrodes has been estimated around 6·10−4 Ω cm2 in the 600–750 °C temperature range, thus lower than the best reported values for the state-of-the-art electrodes featuring sponge-like porosity. The measured impedance data highlighted the higher electrochemical performance of the Ni-impregnated Gd0.1Ce0.9O2 architecture, holding a polarization resistance of 0.823 Ω cm2 at 750 °C, which is regarded as a very promising result for a ∼600 μm thick electrode. The interpretation of the impedance data was supported by the distribution of relaxation times analysis and the complex non-linear least square fit. In particular, the electrochemical investigation highlighted the presence of two major resistive contributions which have been ascribed to the occurrence of a chemical capacitance within the GDC10 lattice (low frequency contribution) and to the multi-layered architecture of the tested symmetrical cells which increases the contact losses (high frequency contribution).