Mass Transfer and Activation Dual Modification Strategy for Fuel Electrode Interfaces in Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOECs) are promising devices that use high-temperature electrolysis to convert H₂O and CO₂ into valuable fuels like H₂ and CO. Compared with conventional electrolysis, SOECs operate at elevated temperatures, which improves efficiency via utilizing industrial waste heat and renewable energy sources. However, CO₂ electrolysis faces challenges due to the chemical stability of CO₂, requiring a high energy input to break its bonds. NiO-YSZ based fuel electrode-supported SOECs are widely used due to their good electrochemical performance and mechanical strength at a high temperature. Nonetheless, some issues such as reduced electrode conductivity, chemical stability, and interface reaction activity during long-term operation hinder their performance and lifespan. It is thus important for the enhancement of gas transport and catalytic activity to optimize the microstructure and composition of the fuel electrode.

In this work, a dual modification strategy for microstructure optimization and impregnation modification was proposed to improve SOEC fuel electrode performance for CO₂ electrolysis. The electrode microstructure was optimized via introducing starch as a pore former during slurry preparation to adjust the porosity and improve gas diffusion. Half-cells consisting of NiO–YSZ support, NiO–YSZ functional layer, and YSZ electrolyte were fabricated by tape casting and sintered at 1350 ℃. In addition, Ce_0.8Gd_0.15Ni_0.05O₂ (CGN) was synthesized by a sol-gel method and impregnated into the porous fuel electrode. After impregnation, samples were reduced in hydrogen to produce Ni nanoparticles dispersed on the Ce-based matrix. The microstructure was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), while the oxygen vacancies and active sites were determined by X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and carbon dioxide temperature programmed desorption (CO₂-TPD). The electrochemical performance was evaluated by impedance spectroscopy and current-voltage measurements.

The introduction of starch effectively increases the electrode porosity, thus reducing mass transfer polarization resistance and enhancing gas transport. The results of electrochemical tests demonstrate that the optimized electrode has a current density of 0.64 A·cm^-2 at 750 ℃ and 1.6 V under CO₂ electrolysis atmosphere. The impregnation of CGN precursor leads to the uniform dispersion of Ni nanoparticles and increases oxygen vacancy concentration. These modifications significantly improves catalytic activity toward CO₂ reduction, and the electrolysis current density is increased by 58% and 64% at 1.1 V and 1.6 V, respectively. The impedance data indicate a marked decrease in polarization resistance. The long-term stability tests over 100 hours show a stable electrochemical performance, indicating that the combined structural and compositional modifications effectively enhance electrode durability and activity.

The dual modification approach integrating microstructural optimization and CGN impregnation significantly enhanced SOEC fuel electrode performance in CO₂ electrolysis. Increased porosity improved gas transport, while Ni catalyst modification boosted catalytic activity and oxygen ion transport. This strategy could provide a practical and cost-effective method to improve SOEC durability and efficiency without using expensive noble metals. The findings could offer a valuable guidance for the development of next-generation high-performance SOEC systems for carbon-neutral energy applications.