Carbon-Supported IrNi Core-Shell Nanoparticles: Synthesis, Characterization, and Catalytic Activity

We synthesized carbon-supported IrNi core- shell nanoparticles by chemical reduction and subsequent thermal annealing in H-2, and verified the formation of Ir shells on IrNi solid solution alloy cores by various experimental methods. The EXAFS analysis is consistent with the model wherein the IrNi nanoparticles are composed of two-layer Ir shells and IrNi alloy cores. In situ XAS revealed that the Ir shells completely protect Ni atoms in the cores from oxidation or dissolution in an acid electrolyte under elevated potentials. The formation of Ir shell during annealing due to thermal segregation is monitored by time-resolved synchrotron XRD measurements, coupled with Rietveld refinement analyses. The H-2 oxidation activity of the IrNi nanoparticles was found to be higher than that of a commercial Pt/C catalyst. This is predominantly due to Ni-core-induced Ir shell contraction that makes the surface less reactive for IrOH formation, and the resulting more metallic Ir surface becomes more active for H-2 oxidation. This new class of core shell nanopartides appears promising for application as hydrogen anode fuel cell electrocatalysts.