Octahedral PtNi nanoparticle catalysts: exceptional oxygen reduction activity by tuning the alloy particle surface composition.

We demonstrate how shape selectivity and optimized surface composition result in exceptional oxygen reduction activity of octahedral PtNi nanoparticles (NPs). The alloy octahedra were obtained by utilizing a facile, completely surfactant-free solvothermal synthesis. We show that the choice of precursor ligands controls the shape, while the reaction time tunes the surface Pt:Ni composition. The 9.5 nm sized PtNi octahedra reached a 10-fold surface area-specific (~3.14 mA/cm(Pt)(2)) as well as an unprecedented 10-fold Pt mass based (~1.45 A/mg(Pt)) activity gain over the state-of-art Pt electrocatalyst, approaching the theoretically predicted limits.