Solid Oxide Cells (SOC) offer an effective and eco-friendly method for hydrogen generation or conversion, with a potential for their integration with renewable energy sources for energy storage and distribution. SOC operating in electrolysis mode are also notable for their capability to produce higher added-value chemicals, such as oxygen, carbon monoxide, syngas, ammonia, or light hydrocarbons by means of the so-called Power to X routes.

Conventional SOC devices use catalytically active Ni-based electrodes, which imposes stringent requirements on the fabrication and operation conditions. In particular, Ni-containing electrodes must be maintained in strongly reducing atmospheres at the fuel side, both during the cell operation or in stand-by mode, in order to prevent nickel oxidation and associated mechanical issues. The concept of symmetric cells (sSOC) proposes utilization of the same electrode material at both oxygen and fuel side, simplifying the procedure of the cell fabrication and improving device tolerance to switching between gases supplied to either electrode. Redox-stable Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) with a notable catalytic activity is considered as a promising electrode material for sSOCs, whereas its application does not require using hydrogen at the fuel electrode side, increasing the safety of the device.

The present study focuses on electrochemical characterization of SFM and SFM-GDC composite as electrodes for electrolyte-supported sSOCs. The cell configuration included dense membranes of 6Yb4ScSZ electrolyte with remarkable ionic conductivity, protective layers of GDC, coated with electrode layers. SFM and SFM-GDC electrodes have a pronounced activity towards steam electrolysis, with a strong influence of water supply to the fuel electrode on the performance. Particularly, small-area SFM/6Yb4ScSZ/SFM symmetric button cells deliver the electrolysis currents up to 1-1.4 A/cm² at a cell voltage of 1.3 V and can operate upon periodic switches between the fuel and air atmospheres. The electrodes are active towards co-electrolysis of H₂O-CO₂ mixture, with somewhat lower activity with respect to CO₂ conversion in comparison with conventional Ni-based composites.

Among the factors affecting the performance and stability of the electrochemical cell, one could highlight the phase stability of the electrode material, mechanical and microstructural features of the electrode layers, especially in hydrogen- and water-containing atmospheres. The cell characteristics are shown to be strongly susceptible towards high-temperature interactions between the components, which necessitates a proper optimization of the fabrication procedure. Deposition of SFM-GDC functional layers improves the mechanical stability of the electrodes, without compromising the electrochemical properties. Optimized procedures of the electrode deposition are currently being implemented for fabrication of large-area (up to 40 cm²) single-repeating units with SFM and SFM-GDC symmetric electrodes.