Effect of Gas Diffusivity in Fuel Electrode on Initial Durability for Solid Oxide Cells during Steam/CO₂ Coelectrolysis

For solid oxide electrolysis cells (SOECs) during steam/CO 2 coelectrolysis, the slopes of current density–voltage curves frequently increase at high current densities due to an increase in gas diffusion overpotential. The gas diffusivity strongly affects the initial performance for coelectrolysis SOECs. The durabilities of SOECs during coelectrolysis are generally lower compared to those of SOECs during steam–only electrolysis and solid oxide fuel cells during power generation. The present work investigates the effect of gas diffusivity in the fuel electrode on the initial durability during coelectrolysis at H 2 O/CO 2 = 2 and 700 °C for fuel electrode–supported microtubular SOECs with varying geometries and using different fuel electrode materials. Upon varying the geometries and materials, high initial performances are observed for cells with low polarization resistances associated with the gas–related processes in the fuel electrode. However, the initial deterioration during coelectrolysis remains unchanged for cells using the same fuel electrode materials with different geometries. Material variations lead to changes in the fuel electrode microstructure, such as the pore size and the pore distribution, which in turn affect the gas diffusivity in the fuel electrode substrate. Additionally, it is found that microstructural variations in the fuel electrode significantly influence the initial durability of coelectrolysis SOECs.