Surface Reconstruction for Forming the [IrO6]-[IrO6] Framework: Key Structure for Stable and Activated OER Performance in Acidic Media.

The surface reconstruction of iridium-based derivatives (AxIryOz) was extensively demonstrated to have an excellent oxygen evolution reaction (OER) performance in an acidic medium. It is urgent to use various spectroscopy and computational methods to explore the electronic state changes in the surface reconstruction process. Herein, the underestimated Lu2Ir2O7 was synthesized and investigated. Four typical forms of electrochemistry impedance spectra involved in the reconstruction process revealed three dominating forms of reconstructed pyrochlore in the OER stage, including the inner intact pyrochlore, mid metastable [IrO6]-[IrO6] framework, and the outer collapse amorphous layer. The enhancing electron transport efficiency of the corner-shared [IrO6]-[IrO6] framework was revealed as a critical role in acidic systems. The density of state (DOS) for the constructed [IrO6]-[IrO6] framework corroborated the enhancement of Ir-O hybridization and the downshift of the d-band center. Additionally, we contrast the pristine and reconstruction properties of the Pr2Ir2O7, Eu2Ir2O7, and Lu2Ir2O7 in alkaline and acidic media. The DOS and the XANES results reveal the scale relationship between the O 2p band center and the intrinsic activity for bulk pyrochlore in alkaline media. The highest O 2p center and the highest Ir-O hybridization of Lu2Ir2O7 exhibited the best OER performance among the Ir-based pyrochlore, up to a ninefold improvement in Ir-mass activity compared to IrO2. Our findings emphasize the electrochemical behavior of the reconstruction process for activated water-splitting performance.