Operando Direct Observation of Stable Water-Oxidation Intermediates on Ca2-xIrO4 Nanocrystals for Efficient Acidic Oxygen Evolution

We report Ca2-xIrO4 nanocrystals exhibit record stability of 300 h continuous operation and high iridium mass activity (248 A g(Ir)(-1) at 1.5 VRHE) that is about 62 times that of benchmark IrO2. Lattice-resolution images and surface-sensitive spectroscopies demonstrate the Ir-rich surface layer (evolved from one-dimensional connected edge-sharing [IrO6] octahedrons) with high relative content of Ir5+ sites, which is responsible for the high activity and long-term stability. Combining operando infrared spectroscopy with X-ray absorption spectroscopy, we report the first direct observation of key intermediates absorbing at 946 cm(-1) (Ir6+=O site) and absorbing at 870 cm(-1 )(Ir6+OO- site) on iridium-based oxides electrocatalysts, and further discover the Ir6+=O and Ir6+OO- intermediates are stable even just from 1.3 VRHE. Density functional theory calculations indicate the catalytic activity of Ca2IrO4 is enhanced remarkably after surface Ca leaching, and suggest IrOO- and Ir=O intermediates can be stabilized on positive charged active sites of Ir-rich surface layer.

Automated summary

We report record stability and high iridium mass activity of Ca2-xIrO4 nanocrystals, with 300 h continuous operation and an activity about 62 times higher than benchmark IrO2. The Ir-rich surface layer, evolved from one-dimensional connected edge-sharing [IrO6] octahedrons, is responsible for the high activity and long-term stability. We also observe key intermediates on iridium-based oxides electrocatalysts and find that they are stable even at low voltages. Density functional theory calculations suggest that the catalytic activity of Ca2IrO4 is enhanced remarkably after surface Ca leaching, allowing for stabilization of IrOO- and Ir=O intermediates on positive charged active sites of the Ir-rich surface layer.