Electrochemical Properties And Single Cell Performance Of Pd Core-Pt Shell Structured Catalyst Synthesized By A Simple Direct Displacement Reaction

A carbon supported Pd core-Pt shell structured catalyst (Pt/Pd/C) was synthesized by a very simple direct displacement reaction (DDR), in which Pd core nanoparticles (NPs) were directly displaced with [PtCl4](2-) on stirring in N-2 saturated H2SO4 aqueous solution at 70 degrees C instead of a modified Cu under potential deposition (Cu-UPD)/Pt displacement method. In DDR, potential difference between Pd core and [PtCl4](2-) was decreased compared with the difference between Cu shell and [PtCl4](2-) in Cu-UPD/Pt displacement method, which suppressed non-uniform Pt shell formation and increased Pt shell coverage, enhancing oxygen reduction reaction (ORR) activity. Furthermore, fine Pd core NPs were preferentially dissolved out by Cl- anions released from [PtCl4](2-) during DDR performed in acidic H2SO4 solution at 70 degrees C and mean diameter of Pd@Pt core-shell NPs increased, improving durability of Pt/Pd/C catalyst by the size effect. Large Pd particles, however, were formed in Pt/Pd/C catalyst through a disproportionation reaction of Pd2+ cations generated in DDR, which was suppressed by addition of Br- anions as complexing agent. A single cell using Pt/Pd/C cathode catalyst synthesized by DDR with Br- anions and activated by H-2-O-2 chemical pretreatment showed 2.4-fold ORR mass activity of a commercially available Pt/C catalyst at a current density of 1.0 A cm(-2). Thus, DDR was considered to be a suitable synthetic method for a mass production of highly active and durable Pt/Pd/C catalyst for ORR. (c) 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.