Experiments and modeling of solid oxide co-electrolysis: Occurrence of CO2 electrolysis and safe operating conditions

Solid Oxide Electrolysis Cell (SOEC) has attracted considerable attention for its potential scalability and high energy conversion efficiency. It is capable of electrolyzing both H2O and CO2 simultaneously, generating syngas that can be further synthesized into carbon-based fuels, which are good energy carriers for long-term energy storage. However, despite its promise, the understanding of the reaction mechanism crucial for extending cell longevity remains incomplete, and concerns persist regarding carbon deposition during co-electrolysis. A dual approach, combining experiments and Multiphysics simulations was adopted to explore the reaction mechanism and carbon deposition risk across a wide range of operating conditions on industrial-size cells. Both experimental observations and simulation results indicate that CO2 electrolysis and carbon deposition are significantly influenced by the inlet water content and flow rates at the fuel electrode. Increasing the inlet H2O concentration and fuel electrode flow rates lead to CO2 electrolysis occurring at higher current densities. Also, carbon deposition, which was found at the interface of fuel electrode and electrolyte, can be mitigated by controlling the conversion rate relative to the inlet H2O content and by increasing the flow rate at the fuel electrode. Additionally, the current density distribution of H2O electrolysis and CO2 electrolysis across the cell were also investigated. The obtained insights hold significance for the practical operation of SOEC co-electrolysis.