Probing ultrathin one-dimensional Pd-Ni nanostructures as oxygen reduction reaction catalysts

An ambient, surfactant-based synthetic means was used to prepare ultrathin binary (d ∼ 2 nm) Pd-Ni nanowires, which were subsequently purified using a novel butylamine-based surfactant-exchange process coupled with an electrochemical CO adsorption and stripping treatment to expose active surface sites. We were able to systematically vary the chemical composition of as-prepared Pd-Ni nanowires from pure elemental Pd to Pd_0.50Ni _0.50 (atomic ratio), as verified using EDS analysis. The overall morphology of samples possessing >60 atom % Pd consisted of individual, discrete one-dimensional nanowires. The electrocatalytic performances of elemental Pd, Pd_0.90Ni_0.10, Pd_0.83Ni _0.17, and Pd_0.75Ni_0.25 nanowires in particular were examined. Our results highlight a "volcano"-type relationship between chemical composition and corresponding ORR activities with Pd _0.90Ni_0.10, yielding the highest activity (i.e., 1.96 mA/cm² at 0.8 V) among all nanowires tested. Moreover, the Pd _0.90Ni_0.10 sample exhibited outstanding methanol tolerance ability. In essence, there was only a relatively minimal 15% loss in the specific activity in the presence of 4 mM methanol, which was significantly better than analogous data on Pt nanoparticles and Pt nanowires. In addition, we also studied ultrathin, core-shell Pt∼Pd_0.90Ni_0.10 nanowires, which exhibited a specific activity of 0.62 mA/cm² and a corresponding mass activity of 1.44 A/mg_Pt at 0.9 V. Moreover, our as-prepared core-shell electrocatalysts maintained excellent electrochemical durability. We postulate that one-dimensional Pd-Ni nanostructures represent a particularly promising platform for designing ORR catalysts with high performance.