Sulfur Impurities in CO_x Feed Gases of Solid Oxide Cells: Effect on Degradation and Removal Strategies

High-temperature solid oxide cells (SOC) offer unrivaled Faradaic and energetic efficiencies for carbon dioxide electrolysis. However, it is yet unclear which contaminant level in carbon monoxide and carbon dioxide feed gases are tolerable to achieve low degradation rates. In this work, electrolyte-supported cells (ESC) with Ni/Gadolinia-doped ceria (Ni/CGO) fuel electrodes were exposed to CO/CO 2 gas mixtures at open circuit voltage. The resistance evolution over time was monitored by means of electrochemical impedance spectroscopy. With this approach it is shown that a degradation over times of up to 96 h occurs. X-ray photoemission spectroscopy (XPS) and high-resolution secondary ion mass spectrometry (SIMS) imaging techniques were used to show that the degradation is related to sulfur impurities on the electrode surface. The results demonstrate the importance of feed gas purity for the commercialization of high-temperature CO 2 electrolysis.