Unconventional High-Index Facet of Iridium Boosts Oxygen Evolution Reaction: How the Facet Matters

Iridium (Ir) nanostructures with well-defined shapes, and particularly, highly active surface, are attractive for the application of electrocatalytic oxygen evolution reaction (OER), yet they have had very limited success to date because of challenges in their synthesis. Here, we report the synthesis of Ir nanocrystals, in the form of Pd@Ir core-shell structures and with well-defined high-index {331} facets, by a robust seed-mediated process. The success relies on the precise control over the deposition of ultrathin Ir layer on Pd trioctahedral nanocrystals. The Pd@Ir nanocatalyst with such unique high-index facets delivers substantially promoted OER activity and durability compared with those with low-index facets (i.e., {100} and {111} facets), with an overpotential as low as 300 mV, boosted mass activities up to 1.01 A mg(Ir)(-1) at 1.53 V, and a minimal Tafel slope of 84.9 mV dec(-1). Density functional theory (DFT) calculations suggest that the superior OER performance originates from the easier hydroxylation of *O to *OOH over high-index facets, along with the appropriate value of Delta G(O)-Delta G(OH) and satisfactory adsorption/desorption property. Moreover, the high-index facets are apt to be electrochemically oxidized into stable IrOx species, leading to an improved durability. Both theoretical and experimental studies demonstrate the fascinating property of a high-index Ir shell in facilitating OER activity and durability.