Size- and Composition-Dependent Enhancement of Electrocatalytic Oxygen Reduction Performance in Ultrathin Palladium–Gold (Pd_1–<i>x</i>Au_<i>x</i>) Nanowires

Abstract

In this report, we examine the composition- and size-dependent performance in hierarchical Pd_1–<i>x</i>Au_<i>x</i> nanowires (NWs) encapsulated with a conformal Pt monolayer shell (Pt∼Pd_1–<i>x</i>Au_<i>x</i>). The ultrathin Pd_1–<i>x</i>Au_<i>x</i> NWs are prepared by a solution-based method wherein the chemical composition can be readily and predictably controlled. Importantly, as-prepared Pd₉Au NWs maintain significantly enhanced oxygen reduction reaction (ORR) activity (0.40 mA/cm²), as compared with elemental Pd NW/C (0.12 mA/cm²) and Pt nanoparticles (NP)/C (0.20 mA/cm²), respectively. After the deposition of a Pt monolayer, a volcano-type composition dependence is observed in the ORR activity of the Pt∼Pd_1–<i>x</i>Au_<i>x</i> NWs as the Au content is increased from 0 to 30% with the activity of the Pt∼Pd₉Au NWs (0.98 mA/cm², 2.54 A/mg_Pt), representing the optimum performance. We note that the platinum group metal activity of the ultrathin 2 nm NWs (0.64 A/mg) is significantly enhanced as compared with that of analogous 50 nm NWs (0.16 A/mg) and commercial Pt NP/C (0.1–0.2 A/mg), thereby highlighting a distinctive size-dependent enhancement in NW performance