Enhanced Durability with Cu-Containing Chemically Ordered Pt-Alloy Catalyst for Oxygen Reduction Reaction in Polymer Electrolyte Fuel Cell

Large-scale commercialization of polymer electrolyte fuel cells (PEFCs) requires great improvement in activity and durability of the cathode catalyst [1]. We have reported enhanced activity and durability of the Pt-based intermetallics, Pt₂FeCo/C, with L1₀ ordered face-centered tetragonal (fct) structure both in acidic solution [2] and as the cathode catalyst of a membrane-electrode assembly [3]. In this work, Cu with higher standard reduction potential was employed to form ordered fct-Pt₂FeCu/C, and its activity of oxygen reduction reaction (ORR) and durability were compared with its counterpart bimetallic catalyst, fct-PtFe/C, and the commercial catalyst from Tanaka Kikinzoku Kogyo (TKK-Pt/C).

Pt₂FeCu/C and PtFe/C were fabricated by the heat treatment of the mixture of metallic precursors and carbon black at 800 °C under 20% H₂ in N₂ for 2 h. The metal content of the catalyst was around 40 wt%. ORR activity of the catalysts was evaluated in 0.1 M HClO₄solution using the rotating disk electrode technique. The durability of the catalysts was examined in the same solution at 60 °C by applying square wave potential cycling, 0.6 V for 3 s and 1.0 V for 3 s, according to load cycle durability testing protocol recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ).

XRD patterns of Pt₂FeCu/C and PtFe/C showed the formation of chemically ordered fct structures. Both the fct catalysts initially showed high mass activity above 0.5 A/mg-Pt. Figure 1 shows the change in electrochemical surface area (ECSA) and mass activity during load-cycle durability test at 60 °C. Cu-containing fct-Pt₂FeCu/C retained more than 70% of mass activity and ECSA at 10K durability cycles, while fct-PtFe/C and TKK-Pt/C catalysts showed a significant loss of activity and ECSA: retention was about 50% for TKK-Pt/C and 40% for fct-PtFe/C. The mass activity of fct-Pt₂FeCu/C catalyst was enhanced by more than twice with respect to TKK-Pt/C catalyst, both at the initial state and after 10K durability cycles. STEM-EDX line-scans of the catalysts before and after durability cycles showed that dissolution of Fe and Cu was much less in fct-Pt₂FeCu/C than in fct-PtFe/C. The enhancement in the durability of the fct-Pt₂FeCu/C catalyst may be ascribed to the synergistic effects of the presence of Cu with higher redox potential and the ordered structure of catalyst.

 References

[1] M.K. Debe, Nature, 486, 43–51 (2012).

[2] B. Arumugam, B. A. Kakade, T. Tamaki, M. Arao, H. Imai, T. Yamaguchi, RSC Advances, 4, 27510–27517 (2014)

[3] T. Tamaki, A. Minagawa, B. Arumugam, B.A. Kakade, T. Yamaguchi, J. Power Sources, 271, 346–353 (2014)