Hydrogen Oxidation Reaction Activity of RuO2 Nanosheets Modified Pt−Ru / C

Abstract

Carbon supported Pt-Ru systems such as PtRu/C and Pt2Ru3/C have been investigated as anode catalysts of polymer electrolyte membrane fuel cells. However, hydrogen oxidation reaction (HOR) activity for Pt-Ru/C is significantly degraded due to adsorption of carbon monoxide (CO) on the active Pt sites and dissolution of Ru. The addition of metal oxide nanosheets enables to enhance the performance of catalysts. We have reported that RuO2 nanosheets [1] as an additive to Pt/C (RuO2ns-Pt/C) and PtRu/C (RuO2ns-PtRu/C) enhances CO tolerance at room temperature [2]. The HOR current of RuO2ns-Pt/C was improved by 25% compared to Pt/C. RuO2ns-PtRu/C had higher HOR activity and enhanced CO tolerance. Thus, CO poisoning is suppressed by the addition of RuO2 nanosheets. However, it is necessary to measure the performances at higher temperature near actual operating of PEFC. In this study, we report the addition effect of RuO2 nanosheets to PtRu/C and Pt2Ru3/C at 25◦C as well as 70◦C. Chronoamperograms (CA) of commercial and RuO2 nanosheests modified catalysts at 25 and 70◦C are shown in Figures A and B. At 25◦C (Fig. A), the addition of RuO2 nanosheets increased the initial HOR activity and the activity after accelerated durability tests (ADT) in 300 ppm CO containing H2 (CO/H2) as well as pure H2. The current was enhanced in the entire range of CA. The addition of RuO2 nanosheets slightly enhanced CO tolerance and durability which were represented by ratio of density current j (in H2) divided by j (initial in CO/H2) and j (initial in CO/H2) divided by j (after ADT in CO/H2), respectively. This behavior is similar to the previous result of comparing RuO2ns-PtRu/C and PtRu/C [2]. The HOR current at 70◦C showed the different behavior compared to 25◦C (Fig. B). At 70◦C, there was a difference of HOR current between composite and commercial catalysts in CO/H2 while HOR activity of the catalysts was almost the same in pure H2. Thus, the decline in HOR current of composite catalysts was slower than non-modified catalysts. Therefore, the composite catalysts suppresses CO adsorption. In particular, the durability of RuO2ns-Pt2Ru3/C at 70◦C shows higher (93%) than the other catalysts (78~86%). This work was supported in part by the “Polymer Electrolyte Fuel Cell Program” from the New Energy and Industrial Technology Development Organization (NEDO), Japan [1] W. Sugimoto, H. Iwata, Y. Yasunaga, Y. Murakami, and Y. Takasu, Angew. Chem. Int. Ed., 42, 4092 (2003). [2] D. Takimoto, T. Ohnishi, and W. Sugimoto, ECS Electrochem. Lett., 4(5), F35-F37 (2015). Figure 1