Solid oxide electrolysis cells (SOECs) represent a highly efficient technology for energy conversion, playing a pivotal role in integrating renewable energy and achieving carbon neutrality goals. However, their performance and durability are critically limited by the microstructure of porous electrodes, where complex multiphysics processes occur. Non-uniform electric field distributions induced by heterogeneous pore structures can lead to localized current crowding, Joule heating and accelerated material degradation. Traditional design approaches often rely on empirical methods, lacking a systematic understanding of the effect of dynamic pore morphology on electric field behavior. Therefore, this study was aimed to elucidate the relationship between the three-dimensional microstructure of porous electrodes and the electric field distribution in SOECs through a combination of advanced characterization and multiscale modeling.

SOEC single cells with a NiO/GDC-SSZ-GDC/LSCF configuration were fabricated by using a multi-step ceramic processing route. Microstructural properties of the electrodes were characterized using field-emission scanning electron microscopy (FE-SEM) and X-ray computed tomography (XCT). High-resolution XCT scanning at 500 nm resolution enabled the reconstruction of 3D pore networks, which were processed using anisotropic diffusion filtering and watershed segmentation in Avizo software. Key morphological parameters, including porosity, pore size distribution, tortuosity and shape factors, were quantified. Based on the reconstructed structures, two-dimensional (2D) and three-dimensional (3D) models were developed using a finite element-based platform. These models incorporated coupled charge conservation and electrochemical kinetics to simulate the electric field and current density distributions under SOEC operating conditions. Both idealized particle-based and fiber-based electrode architectures were generated and compared to evaluate their electrochemical characteristics.

The 3D microstructure analysis results revealed that the NiO fuel electrode had a porosity of 0.3214, with interconnected pores accounting for 91.54% of the total porosity. The average tortuosity was calculated to be 1.2, significantly lower than that reported for typical particle-based electrodes (1.8), indicating the presence of more efficient transport pathways. Simulations results demonstrated that pore morphology is a primary cause of local electric field and current density distortion. Both 2D models and 3D idealized models showed significant fluctuations in electric field strength and potential distribution within the porous electrodes. Crucially, simulations based on the real 3D reconstructed structure identified that the local current density at narrow pore throats was significantly higher than those in other regions, directly confirming that complex pore morphology induced current concentration. Furthermore, the fiber-structured electrode model exhibited more uniform potential and current density distributions, as compared with the particle-based structure, benefiting from continuous conductive paths that reduced contact resistance and transport tortuosity.

It is revealed the intrinsic relationship between the 3D microstructure of porous electrodes and the electric field distribution in SOECs was revealed in this study. The findings underscore the necessity of 3D characterization for accurately assessing electrode transport properties. The simulation results confirmed that complex pore morphology, especially narrow pore throats, acted as a hotspot for current concentration, posing a potential risk for localized degradation. Moreover, the fiber structure, with its continuous conduction paths and low tortuosity, was demonstrated to be a superior electrode architecture for achieving uniform electrochemical performance. The insights and methodologies provide a theoretical basis for the rational design of high-performance SOEC electrodes.

Solid oxide electrolysis cells (SOECs) as a highly efficient energy conversion technology exhibit an immense potential in converting CO₂ into valuable chemicals during the electrolysis process, thereby providing an effective pathway to achieve carbon neutrality goals. However, the inadequate catalytic performance of conventional Ni-YSZ fuel electrode is a pivotal constraint hindering the advancement of SOEC technology. Lanthanum-strontium titanate (LST) perovskite oxides have a superior mixed ionic-electronic conductivity (MEIC) under cathodic polarization, making them a promising alternative fuel electrode for the SOECs. However, the performance of LST in CO₂ reduction reactions (CO₂RR) remains inadequate. In this work, Cu nanoparticles-decorated (La₄Sr₄)_0.9Ti_8-xCu_xO₂₆ (LSTCux, with x=0.4, 0.8, 1.2, and 1.6) layered perovskite oxides as a novel fuel electrode were synthesized by a conventional solid-phase reaction method.

For the synthesis of (La₄Sr₄)_0.9Ti_8-xCu_xO₂₆ (LSTCux, x=0.4, 0.8, 1.2, 1.6), La₂O₃, SrCO₃, TiO₂, and CuO as raw materials were weighed, ground for 2 h, and calcinated at 1400 ℃ for 10 h. Subsequently, the samples were reduced in H₂ atmosphere at 800 ℃ for 10 h, yielding the reduced samples of LSTCu-rx. A solid electrolyte-supported structure was adopted with commercial SSZ electrolyte disks. To prevent reactions, the GDC slurry was spin-coated on the both sides of the SSZ disks and sintered at 1400 ℃ for 3 h to obtain a dense GDC functional layer. LSTCu-rx and LSCF powders were mixed with organic binders to prepare electrode slurries, which were then coated on the both sides of the electrolyte disk and sintered at 900 ℃ for 3 h, resulting in LSTCu-rx|GDC|SSZ|GDC|LSCF structured SOEC button cell. Silver paste and silver wires were applied on the both sides of the cell as current collectors.

The phase compositions of LSTCux and LSTCu-rx were characterized by X-ray diffraction (XRD). The morphology was determined by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). The elemental valence states were determined by X-ray photoelectron spectroscopy (XPS). The electrochemical performance was analyzed by Solartron equipment. CO₂ electrolysis tests were performed on the SOEC button cells via the measurement of j-V curves and electrochemical impedance spectroscopy (EIS).

The results indicate that the electrode exhibits superior electrochemical activity and stability in CO₂ Reduction Reactions (CO₂RR). The results of electrochemical performance tests reveal that at 850 ℃ and 2.0 V, the SOECs utilizing LSTCu-r0.4, LSTCu-r0.8, LSTCu-r1.2, and LSTCu-r1.6 as electrodes have current densities of 1.07, 2.01, 1.65, and 1.52 A/cm², respectively. Among them, LSTCu-r0.8 has the maximum current density with polarization resistance (R_p) and Ohmic resistance (R_Ω) of 0.12 and 0.05 Ω·cm², respectively. These results indicate that LSTCu-r0.8 possesses superior electrocatalytic activity and efficient electron transport.

The LSTCu-rx series of fuel electrodes exhibited superior electrochemical performance and catalytic activity, particularly in the field of CO₂ electrolysis. Among them, LSTCu-r0.8 could be used as a promising material for CO₂ electrolysis fuel electrodes due to its efficient CO₂ adsorption and conversion capabilities, excellent electron transport properties, and stable electrochemical performance. In the future, the further optimization of the preparation process and exploration of a wider range of reaction conditions could be conducted to achieve a more efficient and stable CO₂ electrolysis process.