Authors: Junyi Tao | Gao Yao | Yosuke Komatsu | Anna Ściążko | Takao Okabe | Naoki Shikazono
Source: ECS Meeting Abstracts (article, 2025-07-11)
Field: Materials Science — Materials Chemistry

Study on the Effect of Anode Overpotential on Ni Morphology Changes Using Patterned Ni-YSZ Fuel Electrodes in Solid Oxide Fuel Cells Solid oxide cells (SOCs) are promising energy utilization technologies due to their ability to reversibly convert chemical and electrical energy in solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes [1]. Currently, porous nickel-yttria-stabilized zirconia (Ni-YSZ) cermet is the most widely used material for SOC fuel electrodes [2]. However, due to Ni migration and agglomeration, fuel electrode degradation remains one of the main challenges for SOCs commercialization [3]. The patterned Ni-YSZ fuel electrode can be an effective tool to study Ni migration in solid oxide cells. Triple phase boundary (TPB) determines the electrocatalytic activity of Ni-YSZ fuel electrodes. However, observation and quantification of the changes in TPB due to Ni migration in conventional porous Ni-YSZ composite fuel electrodes are challenging [4]. In contrast, patterned Ni-YSZ fuel electrodes enable direct observation of TPB definition and Ni migration through top-view observation [4-6]. Several hypotheses have been proposed to explain Ni migration in solid oxide fuel cells, including the Gibbs-Thomson effect [7], Ni-YSZ wettability enhancement [4], Ni(OH) x surface diffusion [8], the formation and diffusion of gaseous Ni(OH) 2 [9], and Ni + -ion migration [10] , etc. Although these hypotheses explain aspects of Ni migration to some degree, the underlying mechanisms that trigger Ni migration require further investigation. For instance, dynamic Ni morphology changes have been observed in patterned Ni-YSZ fuel electrodes under operando conditions [11]. Dynamic Ni spreading and splitting up occur periodically under fuel cell mode, while Ni does not move under open circuit and electrolysis cell mode. The results from phase field simulation with physics-informed neural networks suggest that Ni spreading and splitting are several orders of magnitude faster than pure Ni surface diffusion [12]. Overpotential is considered as one of the important causes of Ni migration, in which a threshold overpotential required to trigger this process [8, 13]. For SOEC operation, it is reported that overpotential threshold ranges from 160 mV to 300 mV, with the critical value varying depending on factors such as impurities and particle size, etc. However, for SOFC operation, the overpotential threshold has not been reported so far. For patterned Ni-YSZ fuel electrodes, the relation between anode overpotential and Ni migration remains unclear. Therefore, it is essential to systematically study the effect of anode overpotential on Ni morphology changes. In the present study, ex-situ potentiostatic experiments with varying terminal voltages were conducted on patterned Ni-YSZ cells to investigate the effect of anode overpotential on Ni morphology changes. The patterned Ni-YSZ cells were operated in fuel cell mode with terminal voltages ranging from 0.5 V to 0.7 V, using a fuel gas composition of 92% N 2 , 4% H 2 , and 4% H 2 O at 1073 K. Ni morphology changes were assessed by comparing top-view images of the patterned Ni-YSZ fuel electrode before and after 30 min operation. The anode overpotential was determined by subtracting the ohmic overpotential and cathode overpotential from the total overpotential. The calculated anode overpotential ranges from 0.09 V to 0.24 V. The results demonstrated a discontinuous transition in Ni migration from receding to spreading as the anode overpotential is increased. The effects of gas composition are being studied in the ongoing research. References [1] A. Hauch et al., Science , 370 (2020), 1-8. [2] W. Z. Zhu and S. C. Deevi, Mater. Sci. Eng. A , 362 (2003), 228-239. [3] M. B. Mogensen, Curr. Opin. Electrochem. , 21 (2020), 265-273. [4] Z. Jiao and N. Shikazono, Acta Mater. , 135 (2017), 124-131. [5] Z. Jiao, E. P. Busso and N. Shikazono, J. Electrochem. Soc. , 167 (2020), 024516. [6] Z. Ouyang et al., J. Electrochem. Soc. , 170 (2023), 124511. [7] H.-Y. Chen et al., J. Power Sources , 196 (2011), 1333-1337. [8] M. B. Mogensen et al., Fuel Cells , 21 (2021), 415-429. [9] Y. Lei et al., J. Power Sources , 482 (2021), 228971. [10] M. B. Mogensen and G. Mogensen, ECS Trans. , 112 (2023), 71-80. [11] Z. Ouyang et al., J. Power Sources , 529 (2022), 231228. [12] J. Tao et al., J. Electrochem. Soc. , 171 (2024), 054513. [13] A. Hauch et al., Solid State Ion. , 293 (2016), 27-36. Overpotential ; Anode ; Materials science ; Fuel cells ; Oxide ; Yttria-stabilized zirconia ; Electrode ; Chemical engineering ; Morphology (biology) ; Solid oxide fuel cell ; Metallurgy ; Chemistry ; Electrochemistry ; Cubic zirconia Advancements in Solid Oxide Fuel Cells ; Fuel Cells and Related Materials