Sluggish CO2 reduction on the cathodes of solid oxide electrolysis cells greatly affects electrolysis performance. However, there is no study systematically investigating the cathode functional layer (CFL), where the reduction occurs. Cathode supports equipped with fast gas diffusion channels were employed as a platform to investigate the CFL, including porosity, NiO/(Y2O3)0.08Zr0.92O2 (YSZ) ratio, and thickness. The porosity was adjusted by pore former content, and a higher porosity generated a higher electrolysis current density, while the porosity improvement is limited by the fabrication process. The three-dimensional microstructure of the CFL with different NiO/YSZ ratios was reconstructed by distance correlation functions to estimate three-phase boundary density, which can explain the optimal NiO/YSZ weight ratio of 60:40 for CO2 electrolysis. Increasing CFL thickness can provide more active sites until the optimal thickness of 35 μm. Further increasing the thickness results in gas diffusion limitation. Based on the channeled cathode supports, the CFL was optimized according to CO2 electrolysis performance.
Keywords: CO2 reduction; cathode functional layers; gas diffusion; solid oxide electrolysis cells; three phase boundary.