Iridium–Iron Diatomic Active Sites for Efficient Bifunctional Oxygen Electrocatalysis

Diatomic catalysts, particularly those with heteronuclear active sites, have recently attracted considerable attention for their advantages over single-atom catalysts in reactions involving multielectron transfers. Herein, we report bimetallic iridium–iron diatomic catalysts (IrFe–N–C) derived from metal–organic frameworks in a facile wet chemical synthesis followed by postpyrolysis. We use various advanced characterization techniques to comprehensively confirm the atomic dispersion of Ir and Fe on the nitrogen-doped carbon support and the presence of atomic pairs. The as-obtained IrFe–N–C shows substantially higher electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) when compared to the single-atom counterparts (i.e., Ir–N–C and Fe–N–C), revealing favorable bifunctionality. Consequently, IrFe–N–C is used as an air cathode in zinc–air batteries, which display much better performance than the batteries containing commercial Pt/C + RuO2 benchmark catalysts. Our synchrotron-based X-ray absorption spectroscopy experiments and density functional theory (DFT) calculations suggest that the IrFe dual atoms presumably exist in an IrFeN6 configuration where both Ir and Fe coordinates with four N atoms and two N atoms are shared by the IrN4 and FeN4 moieties. Furthermore, the Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the OER. The dual-atom sites work synergistically, reducing the energy barrier of the rate-determining step and eventually boosting the reversible oxygen electrocatalysis. The IrFe–N–C catalysts hold great potential for use in various electrochemical energy storage and conversion devices.