Microstructural and Electrochemical Characterisation of Degradation in Nickel Impregnated Scandia-Stabilised Zirconia Electrode during Isothermal Annealing

Abstract

In this study, we examine the degradation of nickel impregnated scandia-stabilised zirconia (ScSZ) electrode in wet hydrogen at a working temperature of SOFCs. Continuous van der Pauw measurement was carried out when the electrode was aged at 650 oC in an atmosphere with 5 vol% hydrogen and 95 vol% nitrogen. A fall in sheet conductivity was found in the electrode during ageing within 1000 min. Electrochemical impedance spectra were collected at a constant time intervals during isothermal annealing at 650 oC, 800 oC and 950 oC for the impregnated electrode, at open circuit. Three resistance contributions were decoupled by equivalent circuit fitting, i.e. the ohmic resistance, the anodic reaction resistance, and the gas diffusion resistance. Secondary electron images of electrodes before and after ageing showed an increase in nickel particle size and a decrease in the number of particles, providing microstructural evidence of coarsening. Nickel coarsening was identified as the main mechanism of degradation for the electrode in wet hydrogen.