Preparation of Model SOFCs with Proton-Conducting Electrolyte on Metal Support Using Pulse Laser Deposition

Abstract

Introduction Solid oxide fuel cells (SOFCs) have advantages including no need for using expensive noble metal catalysts, and higher energy conversion efficiency compared to the other types of fuel cells. On the other hand, since their operating temperature ranges from 600 to 1000°C, heat resistance is required for the components, and the materials that can be used for fuel cells are limited to ceramics. Therefore, intermediate temperature (500 to 600°C) SOFCs are of technological interest1-3. Proton-conducting electrolytes such as Yb-doped barium zirconate exhibit sufficiently high protonic conductivity at intermediate temperatures4,5. Furthermore, SOFCs using the proton-conducting electrolytes (p-SOFCs) can operate at a high fuel utilization, because water vapor is formed on the cathode side so that the fuel gas is not diluted on the anode (fuel electrode) side. Previous numerical study has revealed that the p-SOFCs can theoretically generate electric power from the fuels with a conversion efficiency even beyond 80% LHV6. Here in this study, metal-supported p-SOFC model cells are fabricated using Pulse Laser Deposition (PLD) technique, in which p-SOFCs are prepared on supporting porous metal plates with mechanical strength and chemical stability. Technical issues and various fabrication conditions are examined. Experimental Figure 1 schematically shows the structure of a metal-supported p-SOFC model cell prepared in this study. Electrodes were prepared by a screen printing method using NiO-Gd0.1Ce0.9O2-δ (Gd-doped CeO2 denoted as GDC) as the anode material, and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) as the cathode material. As the electrolytes, three types of electrolyte materials were applied, prepared by PLD: oxygen-ion conducting Y2O3-stabilized ZrO2 (YSZ), and proton conducting BaZr0.8Yb0.2O3-δ (BZYb). The model cells were prepared by the following steps: (i) After filling the fuel-supplying holes of the metal support plates, the anode layer was prepared on the plates by the screen printing method. (ii) Using the PLD method, thin electrolyte was deposited on the anode layer. (iii) The cathode layer was then prepared on the electrolyte by the screen printing method. Microstructural characterization and electrochemical measurements were made for the cells prepared by these procedures. Results and discussion A three-layer electrolyte structure of GDC / BZYb / GDC was prepared by using the PLD technique. Figure 2 shows a cross-sectional SEM image of the electrolyte. From this figure, it was confirmed that a dense multi-layer (GDC / BZYb / GDC) electrolyte membrane with a thickness of a few mm could be prepared by the PLD method on the support structure. Electrochemical properties and detailed microstructural observation of such metal-supported p-SOFC model cells fabricated by these procedures will be reported and discussed. References B. C. H. Steele, and A. Heinzel, Nature, 414, 345 (2001). R. Doshi, V. L. Richards, J. D. Carter, X. Wang, and M. Krumpelt, J. Electrochem. Soc., 146 (4), 1273 (1999). M. Gödickemeier, K. Sasaki, L. J. Gauckler, and I. Riess, J. Electrochem. Soc., 144 (5), 1635 (1997). K. D. Kreuer, Chem. Mater., 8 (3), 610 (1996). Y. Matsuzaki, Y. Tachikawa, Y. Baba, K. Sato, H. Iinuma, G. Kojo, H. Matsuo, J. Otomo, H. Matsumoto, S. Taniguch, and K. Sasaki, ECS Trans., 91 (1), 1009 (2019). Y. Matsuzaki, Y. Tachikawa, T. Somekawa, T. Hatae, H. Matsumoto, S. Taniguchi, and K. Sasaki, Sci. Rep., 5, 12640 (2015). Acknowledgement This study is partially supported by the Center of Innovation (COI) program (JPMJCE1318) of the Japan Science and Technology Agency (JST). Figure 1