Phase-Controlled Synthesis of Pd-Sn Nanocrystal Catalysts of Defined Size and Shape

Bimetallic Pd-based nanoparticles (NPs) are of interest as electrocatalysts for formic acid electrooxidation (FAEO) because of their higher initial catalytic activity and CO tolerance when compared to Pt. Intermetallic NPs (i-NPs) with specific geometric and electronic structures generally exhibit superior catalytic activity, selectivity, and durability when compared to their disordered (random alloy) counterparts; however, the colloidal synthesis of i-NPs remains a challenge. Here, a one-pot method was demonstrated as a facile route to obtain monodisperse Pd-Sn NPs with phase control, including intermetallic hexagonal Pd₃Sn₂ (P6₃/mmc), intermetallic orthorhombic Pd₂Sn (Pnma), and alloy cubic Pd₃Sn (FCC, Fm3m) as size-controlled NPs with quasi-spherical shapes. Initial metal precursor ratios and reaction temperature were critical parameters to achieving phase control. Also, slight modifications of synthetic conditions resulted in either Pd₂Sn nanorhombohedra or nanorods with tunable aspect ratios. A systematic evaluation of the Pd-Sn NPs for FAEO showed that most presented higher specific activities when compared to commercial Pd/C, in which Pd₂Sn quasi-spheres and nanorhombohedra showed the highest catalytic activity for FAEO. These results highlight the benefits of phase-controlled Pd-based nanocatalysts with defined nanocrystal size and shape, with use of trioctylphospine (TOP) and oleic acid (OA) central to shape and size control.