Synthesis of Two-Dimensional Nanosheets Catalyst with Ru-Core@Pt-Shell Towards Oxygen Reduction Reaction

Abstract

Improvement in the activity and durability of electrocatalysts for the oxygen reduction reaction (ORR) is an essential issue for wide-spread commercialization of polymer electrolyte fuel cells. Nanoparticle catalysts with alloy, skin, and/or core-shell structures have been developed to improve the activity and durability. However, these nanoparticle catalysts often suffer from degradation under harsh conditions. On the other hand, extended surfaces including thin-films possess high durability; however, the surface area is lower than that of nanoparticles due to low surface area. Nanosheets with atomic thickness have large specific surface area and two dimensionally extended surface. We previously reported the synthesis of metallic ruthenium nanosheets with monoatomic thickness via thermal reduction of RuO2 nanosheets.1,2In this study, we demonstrate the synthesis of Ru-core@Pt-shell nanosheets and the catalytic performance towards the oxygen reduction reaction. Metallic Ru nanosheets supported on carbon composite was prepared via thermal reduction.3 Pt shell was successively formed on metallic Ru nanosheets supported on carbon via galvanic displacement reaction between Cu and Pt2+. The electrochemically active Pt surface area of Ru-core@Pt-shell nanosheets with 3.5 monolayer Pt-shell (Ru@Pt-3.5ML(ns)/C) was 148 m2 (g-Pt)‒1and showed 4.5 times higher activity than benchmark commercial Pt/C catalyst for the oxygen reduction reaction. In addition, the activity retention of Ru@Pt-3.5ML(ns)/C after durability test (0.6-1.0 V and 1.0-1.5 V for 5000 cycles) was higher than that of Pt/C. The high activity could be attributed to the core-shell structure, and the durability originates from the extended surface structure. This research was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. 1) W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, and Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003). 2) K. Fukuda and K. Kumagai, e-Journal Surf. Sci. Nanotechnol., 12, 97 (2014). 3) D. Takimoto, T. Ohnishi, Y. Ayato, D. Mochizuki, and W. Sugimoto, J. Electrochem. Soc., 163, F367 (2016). Figure 1