Facile Synthesis and Characterization of Pd@Ir_nL (n = 1-4) Core-Shell Nanocubes for Highly Efficient Oxygen Evolution in Acidic Media

A simple strategy for developing a cost-effective and efficient Ir-based catalyst toward the oxygen evolution reaction (OER) is to construct a core-shell structure with most of the Ir atoms serving as reactive sites on the surface. However, it has been challenging to achieve a precise control over the thickness of the Ir shell from one to several atomic layers and thus optimize the OER performance. Here, we report a facile synthesis of Pd@Ir_nL (n: the number of Ir atomic layers) core-shell nanocubes with the shell thickness controlled from one to four atomic layers. Their OER activities showed a volcano-type dependence on the number of Ir atomic layers, with a maximum point corresponding to n = 3, which can be attributed to Pd-Ir intermixing, and possible ligand and/or strain effects. Owing to the better passivation for the Pd cores and the formation of a more stable phase during electrolysis, the Pd@Ir_nL nanocubes with thicker Ir overlayers exhibited greater OER durability. The Pd@Ir_3L nanocubes delivered the best activity and durability toward OER with η as low as 245 mV at 10 mA·cm_geo ^-2 and a mass activity of 3.33 A·mg_Ir ^-1 at η = 300 mV. Both values were much better than those of commercial Ir/C and represent the best set of data among the Ir-based core-shell OER catalysts in acidic media.