3R-IrO₂ Two-Dimensional Nanosheets with Varying Layer Spacing and [IrO₆] Distortion for OER

Abstract

Here, two iridium-based crystal structures, K0.3IrO2·xH2O and Rb0.3IrO2·xH2O, have been synthesized for application in the oxygen evolution reaction (OER). The 3R-type layered IrO2 structures with different lattice parameters were successfully obtained from the two Ir structures by the hydrogen ion exchange method. According to synchrotron radiation spectra and the theoretical calculation of density functional theory (DFT), the increase of oxygen vacancy concentration caused by lattice distortion in the 3R-IrO2 crystal is negatively correlated with the activity of OER. A high concentration of oxygen vacancies will reduce Ir–O hybridization, which is not conducive to the balance between the adsorption and desorption of intermediate products. The higher OH adsorption energy barrier and band gap of the 3R-IrO2 crystal limited the improvement of electrochemical performance. In addition, through the analysis of the bonding orbitals and antibonding orbitals of the two structures, we concluded that 3R-IrO2 belongs to the nonthermodynamically stable structure and is not suitable for hydrogen production by electrolysis of water.

Alkali Containing Layered Metal Oxides as Catalysts for the Oxygen Evolution Reaction

“…Thus, a less intense white line indicates more saturation of the 5d states. A lower adsorption energy of the Ir-L 3 edge in K 0.25 IrO 2 compared to IrO 2 confirmed the lower valence state adopted by Ir sites in K 0.25 IrO [107] A combination of XRD and HRTEM measurements show these two materials adopt a layered structure in the hexagonal R � 3m space group with the distance between layers of IrO 2 of 6.9 and 7.0 Å for K 0. 24a, 24b, 24c and 24d).…”