Cerium Silicate Formation in Solid Oxide Electrolysis Cells: Effects on Durability and Mitigation Strategies

Kurzfassung

High-temperature solid oxide electrolysis (SOEL) exhibits superior electrical efficiencies compared to low-temperature electrolysis technologies and possess the unique ability to produce syngas via simultaneous co-electrolysis of steam and carbon dioxide. However, impurity-induced degradation can significantly reduce their lifetime and the requirements for feed gas quality remain unclear. This study presents the first systematic investigation of silicate formation in state-of-the-art Ni/Gadolinium-doped ceria (CGO) fuel electrodes and its severe degradation impact, an issue addressed in multiple German research projects by DLR and Sunfire. Through microstructural and crystallographic analyses, the formation of the cerium silicate phase Ce4.67(SiO4)3O predominantly at the electrolyte|electrode interface is established. A progressive macroscopic color change along the channel is demonstrated to be a reliable indicator for cerium silicate formation. Water quality is identified as a critical factor for minimizing degradation rates. At 860°C, degradation rates of 10.4-14.8 mΩ cm2/kh were observed in single cells operated in co-electrolysis with ultrapure water containing <1 ppb silica, while reverse osmosis water with >40 ppb silica led to a 3-5x acceleration in degradation. The results reveal a highly detrimental solid oxide electrolysis cell (SOEC) degradation mechanism and underscore the necessity of stringent feed water purity to ensure stable long-term stability and commercial viability.