WANG Junbo ¹, DENG Ke ², ZHAO Hongfei ², TANG Qi ¹, ZHANG Yin ¹, JI Chengze ², ZHOU Jun ²

(1. Foshan Power Supply Company of Guangdong Power Grid Co, Foshan 528000, Guangdong, China; 2. Institute of Science and Technology and Education Development, Xi'an Jiaotong University, Xi'an 710049, Shaanxi, China)

Extended abstract:[Background and purposes] 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.[Methods] 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.[Results] 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.[Conclusions] 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.

Key words: solid oxide electrolysis cell (SOEC); porous electrodes; porosity; electric field distribution; three-dimensional reconstruction; multiscale simulation