Tuning the hybridization state of Ir-O to improve the OER activity and stability of iridium pyrochlore via Zn doping

Abstract

Developing high-active, stable, and cost-efficient electrocatalysts for oxygen evolution reaction (OER) is urgent task in water splitting. Recently, iridium pyrochlores (A2Ir2O7) have attracted broad attention as promising catalysts due to their unique electronic properties and the less iridium content relative to IrO2, while in iridium pyrochlores, the relatively high concentration of oxygen vacancies decreases the Ir-O hybridization, hindering the OER process. The electronic states of iridium-based pyrochlore M2Ir2O7 (M = Lu, Pr) are rationally tuned through partial substitution in A-site of Zn2+ for Lu3+ or Pr3+, efficiently promoting its intrinsic activity. The optimal Pr1.8Zn0.2Ir2O7 and Lu1.8Zn0.2Ir2O7 electrocatalysts exhibit 114.6 and 135.32 A gIr−1 high mass activity at 1.58 V vs. RHE. Combining X-ray absorption spectrum with DFT calculations, we demonstrate that the doping of Zn2+ reduces the defective oxygen and regulates the electron distribution. The decrease of defective oxygen leads to the O-2p band center upshift, resulting in the Ir–O covalency promotion and the decrease of the binding energy between oxygen intermediates and Ir to accelerate the OER process. This work provides a fresh idea introducing small ionic radius Zn to solve the problem of high concentration of oxygen vacancies inevitably produced in the synthesis of pyrochlores.