Displacement reduction routed Au-Pt bimetallic nanoparticles: a highly durable electrocatalyst for methanol oxidation and oxygen reduction

In this paper, a new galvanic displacement reduction (GDR) approach was demonstrated for Au-PtNPs synthesis with different Pt:Au compositions in an aqueous medium. PtNPs were initially synthesized by the reduction of H ₂ PtCl ₆ using trisodium citrate and sodium borohydride. Addition of various concentrations of HAuCl ₄ to PtNPs leads to the formation of Au-PtNPs, which follows the GDR between Pt(0) and AuCl ₄ ^- ions. The formation of Au-PtNPs was monitored by UV-vis spectroscopy by tuning the mole ratio of Pt:Au. HR-TEM images showed that the Au-PtNPs were spherical with 11 nm diameter. HR-TEM, XRD and XPS analysis showed that the formed Au-PtNPs were in the form of a core-shell structure. The colloidal Au-PtNPs were then attached on a glassy carbon (GC) electrode via a 1,6-hexanediamine linker for the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). The attachment of Au-PtNPs was further confirmed by XRD, line scanning coupled with energy-dispersive X-ray spectroscopy (EDS) and cyclic voltammetry (CV). The Au-PtNPs modified electrode exhibits a higher heterogeneous electron transfer rate constant of 4.12 × 10 ^-3 cm s ^-1 than bare (1.01 × 10 ^-4 cm s ^-1 ) and PtNP (1.77 × 10 ^-4 cm s ^-1 ) modified GC electrodes. Further, the Au-PtNPs modified electrode exhibited a composition dependent activity towards the MOR and ORR. It was found that the modified electrode with a Pt:Au ratio of 1:0.09 shows 8 times more sensitive oxidation for the MOR when compared to a commercial Pt/C catalyst. The present Au-PtNPs catalyst exhibits a greatly enhanced catalytic activity in terms of mass activity (132 mA mg Pt ^-1 ) and excellent stability relative to the commercial Pt/C catalyst.