Power Generation Charactristics of Polymer Electrolyte Fuel Cells with Electrocatalysts Supported on SnO2 in High Current Density Range

Abstract

Introduction Considerable efforts have been made for FCEV commercialization, for which sufficient performance and durability have to be achieved1. SnO2-supported electrocatalysts with carbon backbone have a potential to achieve both high catalytic activity and high cycling durability2-3. However, it is necessary to further optimize cell performance up to high current densities for such alternative electrocatalysts. By controlling the thickness of the seal material and optimizing the Nafion content of the electrocatalyst layer, successful reduction of various overvoltages and improved power generation performance can be achieved, especially in the high current density region4. This study aims to further improve cell performance at high current densities by varying electrocatalyst layer fabrication conditions and selecting suitable settings for the MEAs. Experimental Using mesoporous carbon (MC) as a support backbone and SnO2 as a support surface layer on the cathode side5, membrane-electrode-assemblies (MEAs) with Pt/Sn0.92Nb0.08O2/MC electrocatalysts were fabricated. On the anode side, a standard Pt/C catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used. Cell performance and overvoltages up to high current densities were measured by varying the size of electrocatalyst particles. Start-stop cycle tests up to 60,000 cycles were also conducted. Results and discussion By ball milling before the Pt loading process in the preparation of the SnO2-supported electrocatalyst Pt/Sn0.98Nb0.02O2/MC, various overvoltages could be reduced, and cell performance became almost comparable to that of the standard Pt/C catalyst. Figure 1 shows the comparison of IV characteristics and Figure 2 shows the comparison of microstructures of electrocatalyst layers. Ball milling resulted in a more appropriate microstructure of the electrocatalyst layer due to the homogenization of the electrocatalyst particle size. As shown in Figure 3, the ECSA retention after 60,000 start-stop cycles was about 50%. Even when MC was used as the support framework, high durability could be achieved due to the presence of SnO2, which was further improved by ball milling. Without ball-milling, the retention was about 45%.In the future, we aim to further improve cell performance by controlling the porous microstructure and water management of the electrocatalysts layer. We will fabricate cells under various conditions, conduct performance tests, and analyze overvoltages. The start-stop and load cycle durability will also be evaluated. Based on these efforts, the latest results of cell performance and durability tests will be presented. Acknowledgment This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).Nakazato, D. Kawachino, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, K. Sasaki, J. Electrochem. Soc., 165, F1154 (2018).Matsumoto, M. Nagamine, Z. Noda, J. Matsuda, S. M. Lyth, A. Hayashi, K. Sasaki, J. Electrochem. Soc., 165, F1164 (2018).Ogawa, Y. Inoue, K. Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara, A. Hayashi, K. Sasaki, ECS Trans., 109 (9), 241 (2022).Inoue, M. Yasutake, Z. Noda, S. M. Lyth, M. Nishihara, A. Hayashi, J. Matsuda, K. Sasaki, ECS Trans., 109 (9), 413 (2022). Figure 1