Enhancement in ORR Activity of Pt/Pd/C Catalyst by Removal of Small Size Pd Core Particles

Tuesday, 7 October 2014
Expo Center, 1st Floor, Center and Right Foyers (Moon Palace Resort)
N. Aoki (Ishifuku Metal Industry), T. NIshikawa, Y. Ikehata, H. Daimon (Faculty of Science and Engineering, Doshisha University), M. Inaba (Department of Molecular Chemistry and Biochemistry, Doshisha University), and H. Inoue (Ishifuku Metal Industry)

PEFCs are attractive energy source because their total well-to-wheel efficiency is higher than that of internal combustion engine [1]. However, the usage of Pt cathode catalyst must be reduced for widespread commercialization. Core-shell structured catalyst is a strong candidate for the reduction, and it has been reported that the ORR activity of a Pt monolayer (PtML) formed on Pd single crystal and on Pd NPs core can be enhanced [2, 3]. So far, we have prepared carbon supported Pd core (Pd/C) by an impregnation and the resulting Pd NPs have a wide size distribution. It was found that the ORR activity of Pd core-Pt shell structured catalyst (Pt/Pd/C) was declined when the catalyst was synthesized using Pd/C core with a smaller mean diameter [4]. In this study, we developed a method removing small Pd NPs to improve the ORR activity of Pt/Pd/C catalyst. The method uses equilibrium potentials of Cu2+/Cu and of O2/H2O (Cu-air treatment), which mimics potential cycling using a potentiostat. The ORR activity of the Pt/Pd/C catalysts synthesized using Pd/C core after the Cu-air treatment was investigated.


A Pd precursor was impregnated on a carbon support and thermally reduced under N2 atmosphere. 300 mg of the Pd/C core (Pd mean diameter: 3.8 nm, 34 wt.%) was dispersed in 0.1 M H2SO4 containing 10 mM CuSO4 and stirred at 30°C for 5 h with and without coexistence of a metallic Cu sheet under air bubbling (Cu-air and air treatments, respectively). The treated Pd/C core was re-dispersed in 0.05 M H2SO4 containing 10 mM CuSO4 and stirred for 5 h at 5°C with coexistence of a Cu sheet under Ar bubbling to form Cu shell on the Pd core surface (Modified Cu-UPD method [5]). Then, the Cu mesh was removed and K2PtCl4 was added at 5°C to replace Cu shell with Pt, obtaining Pt/Pd/C catalyst. The Pt/Pd/C catalyst was characterized with TG, XRD, XRF, TEM and CV. ORR activity of the catalyst was evaluated with the RDE technique in O2 saturated 0.1M HClO4 at 25°C. Accelerated durability tests (ADTs) were performed using rectangular potential cycling (0.6 V 1.0 V vs. RHE) in Ar saturated 0.1 M HClO4at 80°C for 10,000 cycles.

Results and Discussion

Figure 1 shows TEM images of Pd/C cores. The mean diameter of the Pd/C core after the Cu-air treatment increased slightly (3.8 → 4.2 nm). On the contrary, the mean diameter after the air treatment showed little change. Table 1 summarizes the mean diameters and Pd loadings of the Pd/C cores. The Pd loading after the Cu-air treatment decreased by 30 % from that of the pristine Pd/C core, while the loading decreased by only 7 % after the air treatment. These results suggest that the smaller Pd core NPs were removed by the Cu-air treatment. Figure 2 depicts CV of the original Pd/C core. The onset potential for Pd oxide formation was ca. 0.75 V vs. RHE and the oxide was reduced at ca. 0.50 V vs. RHE. During the Cu-air treatment, the Cu2+/Cu equilibrium potential (ca. 0.3 V) is applied to the Pd/C core when the core contacts with the metallic Cu sheet and the potential for O2/H2O (ca. 1.0 V) is applied when the core is in the solution. On the contrary, only ca. 1.0 V is applied to the core in the air treatment. The increase in mean diameter and the decrease in Pd loading of the Pd/C core after the Cu-air treatment are considered to be caused by repeated potential cycling across the redox potentials of Pd.

ORR mass activity of Pt/Pd/C catalysts is summarized in Fig. 3. There are little differences in the initial ORR mass activities among the Pt/Pd/C catalysts, whereas the Pt/Pd/C catalysts synthesized using the Pd/C core after the Cu-air treatment exhibited higher ORR activity after the ADT at 80°C. These results imply that the removal of the small size Pd NPs by the Cu-air treatment is an effective method to enhance the ORR activity of Pt/Pd/C catalyst, especially the activity after the ADT at 80°C.


This work was supported by New Energy and Industrial Technology Development Organization (NEDO), Japan.


[1] B. G. Pollet et al., Electrochim. Acta, 84, 235 (2012).

[2] J. Zhang et al., J. Phys. Chem. B, 108, 10955 (2004).

[3] J. Zhang et al., Angew. Chem. Int. Ed., 44, 2132 (2005).

[4] N. Aoki et al., 54thBattery Symposium, Abstract 2H18, Osaka, Japan (2013).

[5] Y. Ikehata et al., 224thECS Meeting, Abstract #1497,

San Francisco, USA (2013)