Molten salt synthesis of carbon-supported Pt–rare earth metal nanoalloy catalysts for oxygen reduction reaction

Abstract

The synthesis of nano-sized alloys of Pt and rare earth (RE) metal catalysts has been a huge challenge due to a significantly large standard reduction potential difference of Pt and RE metals and the high synthesis temperature. Pt_xY/C catalysts with an average particle size of around 21 nm, were synthesized by mixing K₂PtCl₄ with Y₂O₃ (a molar ratio of Pt : Y = 1 : 1) with a carbon support in a molten LiCl–CaH₂ system by a one-step molten salt synthesis method at 600 °C. The synthesis processes of the Pt_xY/C alloys are proposed as follows: Pt nanoparticles were first obtained by the reaction of K₂PtCl₄ and CaH₂ at 210 °C, then Y ions were preferentially reduced on the Pt nanoparticle surface by the reduction of CaH₂, followed by Pt_xY alloy formation in the molten LiCl–CaH₂ system at 600 °C. Molten LiCl provides a strong reducing environment and lowers the formation temperature of alloys. Pt₂Gd/C and Pt₂La/C were also obtained with Gd₂O₃ and La₂O₃ as the starting raw materials, respectively by using the same process. When investigated as an electrocatalyst for the oxygen reduction reaction (ORR), the half-wave potentials of Pt_xRE/Cs are all more positive than that of commercial Pt/C catalyst (e.g., 0.905 V for Pt_xY/C while 0.880 V for JM Pt/C), and the nano-sized Pt_xY/C alloy shows higher electrocatalytic activity toward the ORR and preferable catalytic durability with respect to JM Pt/C catalysts. This facile synthesis method provides an effective strategy for the preparation of Pt–RE based multicomponent nanoalloys, especially in large-scale production.