Ru-Core@Pt-Shell Nanosheet Anode Catalyst: High Activity and Durability for Hydrogen Oxidation Reaction in the Presence of CO

Abstract

PtRu alloy nanoparticles are presently used as the anode catalyst for residential polymer electrolyte fuel cells due to its high carbon monoxide (CO) tolerance. Unfortunately, PtRu alloy is not as stable as pure Pt, and the gradual dissolution of Ru from the catalyst surface leads to catalyst degradation. In an earlier study, we have shown that the addition of metal or metal oxide nanosheets as co-catalysts to carbon supported PtRu/C catalysts can enhance the CO tolerance and durability 1,2. Here we describe the synthesis of Ru-core@Pt-shell nanosheets via surface limited redox replacement 3. The CO tolerance and durability of Ru-core@Pt-shell nanosheets towards the hydrogen oxidation reaction activity in the presence of CO is presented. Metallic Ru nanosheets supported on carbon composite was prepared via thermal reduction 2. Pt shell was successively formed on metallic Ru nanosheets via galvanic displacement reaction between Cu and Pt2+ by repeating the displacement reaction twice. The electrochemically active PtRu surface area of Ru-core@Pt-shell nanosheets with 1.5 monolayer Pt-shell (Ru@Pt-1.5ML(ns)/C) was 95 m2 (g-PtRu)-1, and the hydrogen oxidation reaction activity in pure H2 of Ru@Pt-1.5ML(ns)/C was 2.4 times higher than benchmark commercial PtRu/C. The H2 oxidation activity in the presence of 300 ppm CO for core-shell nanosheets was 1.5 times higher than that of PtRu/C. In addition, the activity of Ru@Pt-1.5ML(ns)/C after durability test (0.05 (3sec)-0.40 V (3 sec) for 1000 cycles) was 2.0 and 2.3 times higher than that of PtRu/C and Pt/C, respectively. The high activity in pure H2 could be attributed to the large surface area of core-shell structure, and the enhanced CO tolerance could be attributed to the electronic effect from the Ru nanosheet core. Ru nanosheet core was completely covered with Pt-shell, thus, the degradation of activity due to dissolution of Ru was suppressed. 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) D. Takimoto, T. Ohnishi, and W. Sugimoto, ECS Electrochem. Lett., 4, F35 (2015). 2) D. Takimoto, T. Ohnishi, Y. Ayato, D. Mochizuki, and W. Sugimoto, J. Electrochem. Soc., 163, F367 (2016). 3) J. Nutariya, M. Fayette, N. Dimitrov, and N. Vasiljevic, Electrochim. Acta, 112, 813 (2013). Figure 1