Unravelling the role of Si and Al impurities in Ni/YSZ fuel electrode degradation in solid oxide electrolysis cells

Abstract

Global climate concerns from fossil fuel use have increased the demand for sustainable energy storage technologies. Solid oxide electrolysis cells (SOECs), operating at high temperatures (500–900 °C), offer high efficiency and cost-effectiveness but suffer from degradation challenges, particularly in nickel–yttria stabilized zirconia (Ni/YSZ) electrodes. Understanding the degradation mechanisms is critical for improving long-term performance. In this study, the impact of silicon (Si) and aluminum (Al) impurities, commonly introduced through components like gas seals, insulation materials, and manufacturing additives, on the electrochemical performance and microstructure of Ni/YSZ-supported SOECs was investigated. An accelerated testing approach was employed by applying a contaminated nickel contact layer containing Si and Al on the top of the fuel electrode surface, and the cell performance was compared with an uncontaminated reference cell. Through comprehensive electrochemical and microstructural analyses, distinct degradation patterns were identified, and correlations between impurity distribution, local electrochemical conditions, and performance loss were established. A possible mechanism of Si poisoning is proposed in this research, where Si(OH)₄ species undergo temperature and steam-dependent transport before depositing as SiO₂ at triple phase boundaries. This SiO₂ subsequently undergoes electrochemical reduction and incorporates into nickel particles under high overpotential and low interface oxygen partial pressure conditions. These mechanistic insights provide strategies for mitigating impurity effects and improving cell performance in practical SOEC applications.