Bifunctional Electrocatalytic Activity of Ordered Intermetallics Based on Pd and Sn

Abstract

Structurally ordered intermetallic compounds are proven to be very promising for electrocatalysis owing to the homogeneous distribution of active sites, thermodynamic stability, and resistance toward surface rearrangement. Herein, we demonstrate a facile route for the synthesis of Sn- and Pd-based ordered intermetallics hybridized with reduced graphene oxide (rGO) and their bifunctional electrocatalytic performance toward oxygen reduction (ORR) and ethylene glycol oxidation reactions (EGOR). The coreduction of SnCl2 and K2PdCl4 in 1,5-pentanediol in the presence of graphene oxide and the subsequent thermal annealing in an inert atmosphere affords rGO hybridized intermetallics of three phases: primitive orthorhombic PdSn, base-centered orthorhombic PdSn2, and hexagonal Pd3Sn2. The electrocatalytic performance of the hybrid intermetallics toward EGOR and ORR is evaluated in alkaline and acidic electrolytes. Among the three intermetallics, PdSn has excellent electrocatalytic performance toward EGOR and ORR The PdSn/rGO hybrid catalyst outperforms the other two intermetallics toward EGOR in alkaline pH and ORR in acidic as well as alkaline pH in terms of onset potential and mass specific activity. The enhanced performance of PdSn/rGO catalyst is attributed to (i) a change in the Pd d-band center, (ii) a Pd-Pd interatomic distance in a unit cell, and (iii) weak adsorption of in-situ-generated oxygen-containing intermediates species. The lattice strain due to the presence of dissimilarly sized Sn and Pd in a unit cell and the high oxophilicity of Sn downshifts the d-band center of Pd and facilitate the electron transfer kinetics. The catalyst support, rGO, prevents the unwanted aggregation of the active catalyst. The density functional theory calculations show that the oxygen-containing species weakly adsorb on the PdSn surface compared to the other intermetallics, supporting the high electrocatalytic activity of PdSn/rGO.