Carbon Deposition Induced Short Circuit of YSZ Electrolyte in Solid Oxide CO2 Electrolysis

Carbon deposition during the co-electrolysis of CO2 in solid oxide electrolysis cells (SOECs) poses a serious threat to cell structural integrity. Traditionally, it has been believed that carbon accumulates at the interface between the fuel electrode and the electrolyte. However, in this work, we report a novel phenomenon: the occurrence of internal short-circuiting during carbon deposition. This is evidenced electrochemically by a drop in open circuit voltage (OCV), the appearance of an inductive arc or abnormally low impedance in the low-frequency region, and an irreversible degradation that cannot be recovered by operation in pure H2 or in SOFC mode. Post-mortem characterization suggests that elemental carbon may have bridged across the electrolyte, causing an internal short circuit. A possible mechanism for the migration of carbon from the fuel electrode into the electrolyte is proposed and the carbon despotion pathway is analyzed through thermodynamic analysis and multiphysics simulation. Furthermore, a long-term co-electrolysis stability test lasting 1873 hours demonstrated that in the absence of carbon deposition, such short-circuiting behavior was not observed. This finding reinforces the critical importance of preventing carbon deposition to ensure safe and stable SOEC operation, particularly due to the newly identified carbon-bridge-induced short-circuit mechanism.