Strain Regulation to Optimize the Acidic Water Oxidation Performance of Atomic‐Layer IrO x

: Strain regulation has become an important strategy to tune the surface chemistry and optimize the catalytic performance of nanocatalysts. Herein, the construction of atomic-layer IrOx on IrCo nanodendrites with tunable IrO bond length by compressive strain effect for oxygen evolution reaction (OER) in acidic environment is demonstrated. Evidenced from in situ extended X-ray absorption fine structure, it is shown that the compressive strain of the IrOx layer on the IrCo nanodendrites decreases gradually from 2.51% to the unstrained state with atomic layer growth (from ≈2 to ≈9 atomic layers of IrOx ), resulting in the variation of the IrO bond length from shortened 1.94 A to normal 1.99 A. The ≈3 atomic-layer IrOx on IrCo nanodendrites with an IrO bond length of 1.96 A (1.51% strain) exhibits the optimal OER activity compared to the higher-strained (2.51%, ≈2 atomic-layer IrOx ) and unstrained (>6 atomic-layer IrOx ) counterparts, with an overpotential of only 247 mV to achieve a current density of 10 mA cm-2 . Density functional theory calculations reveal that the precisely tuned compressive strain effect balances the adsorbate-substrate interaction and facilitates the rate-determining step to form HOO*, thus assuring the best performance of the three atomic-layer IrOx for OER.