Authors: Anna Ściążko | Yosuke Komatsu | Zewei Lyu | Takaaki Shimura | Naoki Shikazono
Source: ECS Meeting Abstracts (article, 2025-11-24)
Field: Materials Science — Materials Chemistry

Microstructure and YSZ Stability in Nickel Redox-Induced Degradation of Solid Oxide Cells Solid oxide cells (SOCs) enable efficient direct conversion of hydrocarbon fuels to electricity in fuel cell mode (SOFC) and fuel production from electricity in electrolysis mode (SOEC). However, long-term operation leads to microstructural degradation of electrodes, deteriorating electrochemical performance. While Ni-free electrodes are gaining attention [1], Ni-based cermets such as Ni-YSZ and Ni-GDC remain the most widely used fuel electrodes. One of the major degradation mechanisms in these anodes is redox cycling, which affects both the electron-conducting Ni network and the ion-conducting ceramic backbone. The extent of degradation depends on redox conditions (temperature, oxygen partial pressure) and the initial microstructure [2]. In this study, redox-induced degradation in a Ni-YSZ electrode is investigated, focusing on the role of initial porosity on the microstructure and stability of YSZ skeleton. Electrodes were fabricated via screen printing on commercial YSZ pellets and sintered at 1350°C (Ni-YSZ1350) and 1450°C (Ni-YSZ1450), yielding 35% and 22% porosity after reduction, respectively. Cells underwent accelerated redox cycling at 800°C, alternating between oxidation in pure O₂ (2 h) and reduction in pure H₂ (1 h). Electrochemical impedance spectroscopy (EIS) was performed after each cycle to assess performance degradation. Microstructural evolution was observed by post-mortem analyses using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and high-resolution focus ion beam – scanning electron microscopy (FIB-SEM). The experiments revealed distinct degradation patterns in Ni-YSZ1350 and Ni-YSZ1450, as shown in Fig. 1A-B. Ni-YSZ1350 exhibited initial performance improvement during the first three redox cycles, followed by gradual degradation. This initial enhancement is attributed to the formation of nano-Ni particles, increasing the triple-phase boundary (TPB), a phenomenon previously reported by Song et al. [3]. In contrast, Ni-YSZ1450 experienced drastic degradation after the first redox cycle, suggesting lower redox tolerance due to its denser microstructure. Microstructural inspection revealed multiple degradation mechanisms. Cracking of the YSZ backbone induced by Ni volume expansion during oxidation was more pronounced in Ni-YSZ1450, leading to increased ionic resistance and TPB loss. Additionally, a significant number of nano-Ni and YSZ particles were observed, supporting the hypothesis that localized redistribution of phases plays a role in the performance evolution. A closer examination of Ni-YSZ1450 after 20 redox cycles revealed intriguing YSZ morphological changes, as shown in Fig. 1C-D. Large expansion and contraction of the electrode were observed, resulting in fractures and reconnections of the YSZ network during cycling. In the oxidized state, Ni was pushed into the nano-cracks within the YSZ framework (Fig. 1C). Interestingly, following the reduction step, newly formed disconnected pores appeared in the YSZ network, containing embedded nano-Ni particles, suggesting that certain nano-YSZ cracks could partially reconnect upon re-reduction (Fig. 1D). This study further investigates electrochemically induced redox degradation in anode-supported cells, where local high current densities and fuel starvation create severe nano-cracking of the YSZ backbone near the electrolyte, ultimately leading to electrolyte delamination. Moreover, the attempt is taken to predict microstructural and performance degradation under redox cycling by neural network models (UNIT [4] for microstructure evolution and LSTM [5] for performance prediction). Acknowledgments This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan Society for Promotion of Science (JSPS, KAKENHI 23K13261) and by Advanced Research Infrastructure for Materials and Nanotechnology in Japan (ARIM Japan). References: [1] A. Sciazko, Y. Komatsu, R. Yokoi, T. Shimura, N. Shikazono, Journal of the European Ceramic Society , 42 (4), 1556-1567, (2022). https://doi:10.1016/j.jeurceramsoc.2021.11.039 [2] K. Sato, S. Watanabe, Y. Huang, et al. SN Applied Sciences , 3, 810 (2021). https://doi.org/10.1007/s42452-021-04789-w [3] B. Song, E. Ruiz-Trejo, Antonio Bertei, Nigel P. Brandon, Journal of Power Sources , 374, 61-68 (2018). https://doi.org/10.1016/j.jpowsour.2017.11.024 [4] A. Sciazko, Y. Komatsu, T. Shimura, N. Shikazono, npj Computational Materials , 10, 49 (2024). https://doi:10.1038/s41524-024-01228-3 [5] Z. Lyu, Y. Wang, A. Sciazko, H. Li, Y. Komatsu, Z. Sun, K. Sun, N. Shikazono, M. Han, Journal of Energy Chemistry , 87, 32-41 (2023). https://doi.org/10.1016/j.jechem.2023.08.028 Figure Captions Figure 1. Microstructures of as sintered, as reduced and after 20 redox cycles samples, and EIS measurements for Ni-YSZ samples sintered at A) 1350 o C and B) 1450 o C. Magnified microstructures of Ni-YSZ sample sintered at 1450 o C after 20 redox cycles in C) oxidized and D) reduced states. Red arrows indicate cracks in YSZ, green arrows indicate Ni intrusions into YSZ cracks, blue arrow indicates newly formed separated pores in YSZ. Figure 1 Microstructure ; Yttria-stabilized zirconia ; Scanning electron microscope ; Dielectric spectroscopy ; Solid oxide fuel cell ; Redox ; Anode ; Degradation (telecommunications) Advancements in Solid Oxide Fuel Cells ; High-Temperature Coating Behaviors ; Chemical Looping and Thermochemical Processes