Ultrahigh-loading of Ir single atoms on NiO matrix to dramatically enhance oxygen evolution reaction.

Engineering single-atom electrocatalysts with high-loading amount hold great promise in energy conversion and storage application. Herein, we report a facile and economical approach to achieve an unprecedented high-loading of single Ir atoms, up to ~18wt%, on the nickel oxide (NiO) matrix as the electrocatalyst for oxygen evolution reaction (OER). It exhibits an overpotential of 215 mV at 10 mA cm-2 and a remarkable OER current density in alkaline electrolyte, surpassing NiO and commercial IrO2 by 57 times and 24 times at 1.49 V vs. RHE, respectively. Systematic characterizations, including X-ray absorption spectroscopy and aberration-corrected Z-contrast imaging, demonstrates that the Ir-atoms are atomically dispersed at the outermost surface of NiO and are stabilized by covalent Ir-O bonding, which induces the isolated Ir atoms at a favorable over 4+ oxidation state. Density functional theory calculations reveal that the substituted single Ir atom not only serves as the active site for OER but also activates the surface reactivity of NiO, which thus leads to the dramatically improved OER performance. This synthesis method of developing high-loading single-atom catalysts can be extended to other oxide supports and paves the way for industrial application of single-atom catalysts.