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

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 x Y/C catalysts with an average particle size of around 21 nm, were synthesized by mixing K 2 PtCl 4 with Y 2 O 3 (a molar ratio of Pt : Y = 1 : 1) with a carbon support in a molten LiCl-CaH 2 system by a one-step molten salt synthesis method at 600 °C. The synthesis processes of the Pt x Y/C alloys are proposed as follows: Pt nanoparticles were first obtained by the reaction of K 2 PtCl 4 and CaH 2 at 210 °C, then Y ions were preferentially reduced on the Pt nanoparticle surface by the reduction of CaH 2 , followed by Pt x Y alloy formation in the molten LiCl-CaH 2 system at 600 °C. Molten LiCl provides a strong reducing environment and lowers the formation temperature of alloys. Pt 2 Gd/C and Pt 2 La/C were also obtained with Gd 2 O 3 and La 2 O 3 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 x RE/Cs are all more positive than that of commercial Pt/C catalyst ( e.g. , 0.905 V for Pt x Y/C while 0.880 V for JM Pt/C), and the nano-sized Pt x Y/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. The synthesis mechanism of Pt-RE nanoalloy particles prepared by one-step molten salt synthesis as an advanced ORR catalyst is proposed.