Abstract:

Solid oxide cell (SOC) is a typical multi-layer thin film ceramic device consisting of oxygen electrodes, electrolytes, and hydrogen electrodes. The currently widely used structure is a single cell supported by a Ni-YSZ (Nickel-Yttria Stabilized Zirconia) hydrogen electrode, with YSZ (Yttria Stabilized Zirconia) serving as the electrolyte. This configuration achieves electrolyte filmization, while also reducing the operating temperature of the cell. However, it introduces significant diffusion impedance within the hydrogen electrode, which is considered the main reason for the electrochemical asymmetry in reversible solid oxide cell (R-SOC). This study prepared hydrogen electrodes with varying porosity and investigated the impact of diffusion impedance of hydrogen electrodes on R-SOC asymmetry. On this basis, hydrothermal in situ growth technology was employed to prepare ultra-thin and dense GDC (Gd₂O₃ doped CeO₂) barrier layers, compared with conventional screen-printed barrier layers to explore the effect of electrolyte ohmic impedance on electrochemical asymmetry. Experimental findings revealed that the electrolyte ohmic impedance is also a significant factor affecting the electrochemical asymmetry of reversible SOC, and the synergistic mechanism of the diffusion impedance of hydrogen electrodes and the ohmic impedance of thin film electrolytes on this asymmetry was elucidated. The experimental results show that increasing the hydrogen electrode porosity and reducing the electrolyte ohmic impedance can both enhance the R-SOC performance, particularly improving SOEC electrolysis performance, and both have the effect of reducing asymmetry. At 750 ℃, 50% H₂O, and ±0.3 V bias conditions, the single cell with a large-pore hydrogen electrode and a thin film barrier layer exhibited a discharge current density of 0.752 A∙cm⁻² and an electrolysis current density of 0.635 A∙cm⁻². Compared to the single cell with a small pore hydrogen electrode and an ordinary screen-printed barrier layer, the discharge and electrolysis performance of the cell have been improved by ~37% and ~140%, respectively. At the same time, the current density asymmetry of the cell (∆j) under these conditions was only 0.117 A∙cm⁻², reduced by 58% compared to a small porosity hydrogen electrode single cell and 24% compared to a large ohmic impedance single cell. In addition, the study noted that R-SOC asymmetry increases with operating temperature and decreases with higher steam content in the fuel on the hydrogen electrode side. These findings hold significant reference value the design, preparation, and reversible operation of high-performance hydrogen electrode supported thin film electrolyte SOC single cell structures.

Key words: Reversible solid oxide cell, Electrochemical asymmetry, Hydrogen electrode diffusion impedance, Ohmic impedance, Thin film barrier layer