Time-Dependence of Microstructural Evolution and Performance Degradation of Ni/YSZ Electrode in Co-Electrolysis SOEC

Production of synthetic hydrocarbon fuels with Co-electrolysis using solid oxide electrolysis cell (SOEC) by Fischer-Tropsch reaction has attracted attention to solving energy and environmental problems. Reduction of CO 2 and H 2 O to CO and H 2 like a simple reaction process. However, carbon coking and microstructure alteration due to long-term operation could cause degradation performance, especially at Ni/YSZ fuel electrode. In this study, we determined the microstructure evolution and performance degradation of fuel electrode supported SOEC (Nexceris, USA) as function of temperature under 10% H 2 O:20%CO 2 and applied voltage of -1.3 Volt. As a result, lower temperatures (1023 K) degradation showed faster degradation rate than higher temperatures (1073 K) despite similar fuel composition. Post-mortem analysis by SEM-EDX showed that the amount of carbon deposition is relatively low. However, the Ni average diameter increase by factor of two compared to as-reduced Ni/YSZ fuel electrode. Another measurement was conducted to confirm the effect of the water vapor only. It showed that the Ni average diameter was observed to be similar between co-electrolysis and water electrolysis conditions. This result indicated that the change of the Ni average diameter could be affected by the presence of water vapor only. There have been many reports on the change of Ni diameter in the Ni/YSZ for SOEC [1,2]. The Ni migration/diffusion in the Ni/YSZ fuel electrode is a complex mechanism, especially at the porous body because the complex geometry and morphology. Thus, it is so often to use model electrodes to simplify the geometry in order to understand the Ni migration [3]. The YSZ film was deposited on the MgO single crystal by pulsed-laser deposition (PLD). After that, the Ni film sputtered onto YSZ thin film, then patterned by photolithography. The Ni-pattern electrode can be viewed as a simplified cross-section of a porous electrode and simulated on a flat surface. It has two side Ni patterns in the opposite direction which are separated by a small gap on YSZ film which works as the electrolyte. At the edge of the Ni-pattern electrodes, the Pt electrodes were sputtered as a current collector. The model electrode was measured by applying a voltage on two-side of the Ni-patterned electrode where one Ni pattern was in fuel cell mode and another Ni pattern was in electrolysis mode. The measurement was completed under various gas composition at 1173 K. The measurement was taken every 20 h – 40 h before the laser microscope was used to observe the change in the Ni pattern electrode. The result on the model electrode will be corroborated with our study on Ni/YSZ porous. Acknowledgement This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. Reference: [1] A. Hauch, S. D. Ebbesen, S. H. Jensen, M. Mogensen, J. Electrochem. Soc. , 155(11) (2008) B1184-B1193. [2] D. The, S. Grieshammer, M. Schroeder, M. Martin, M. A. Daroukh, F. Tietz, J. Schefold, A. Brisse, J. Power Sources , 275 (2015) 901-911. [3] Z. Ouyang, Y. Komatsu, A. Sciazko, J. Onishi, K. Nishimura, N. Shikazono, J. Power Sources , 529 (2022) 231228.