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 x Y/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 x Y/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 x Y 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 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.