Microstructural Changes in Ni-YSZ Electrodes Operated in Fuel Cell and Electrolysis Modes: Effect of Gas Diffusion Limitations

Abstract

Ni-YSZ electrode support symmetric cells were operated at 0, 0.75, 1.00, and 1.50 A/cm2 for 1000 h in 50% H2-50% H2O at 800 ˚C. Electrochemical fracture at the anode-electrolyte interface is observed to occur under high anodic overpotential. Ni migration is observed and quantified over time at the anode of the polarized cells; however, the cathode shows no migration compared to control. Gas diffusion calculations show that steam is significantly enriched and depleted at the anode and cathode respectively, leading to the formation or suppression of volatile Ni(OH)x species, which have been hypothesized as a transport pathway for Ni. However; gas flux calculations show that chemical evaporation alone is unlikely to be fast enough to induce the Ni loss observed.