Iridium Single Atoms to Nanoparticles: Nurturing the Local Synergy with Cobalt-Oxide Supported Palladium Nanoparticles for Oxygen Reduction Reaction

A ternarycatalyst comprising Iridium (Ir) single-atoms (SA)s decorated on the Co-oxide supported palladium (Pd) nanoparticles (denoted asCPI-SA) is developed in this work. TheCPI-SA with1 wt.% of Ir exhibits unprecedented high massactivity(MA) of 7173 and 770mA mgIr−1, respectively, at 0.85 and 0.90V versus RHE in alkaline ORR (0.1m KOH), outperforming the commercial Johnson Matthey Pt catalyst (J.M.-Pt/C; 20wt.%Pt) by 107-folds. More importantly, the high structural reliability of the Ir single-atoms endows the CPI-SA with outstanding durability, where it shows progressively increasing MA of 13342 and 1372mA mgIr−1, respectively, at0.85 and 0.90V  versus RHE up to 69000 cycles (3months) in the accelerated degradation test (ADT). Evidence from the insitu partial fluorescence yield X-rayabsorption spectroscopy (PFY-XAS) and the electrochemical analysisindicate that the Ir single-atoms and adjacent Pd domains synergistically promote the O2 splitting and subsequent desorptionof hydroxide ions(OH−), respectively.  Whereas the Co-atoms underneath serve aselectron injectors to boost the ORR activity of the Irsingle-atoms. Besides, a progressive and sharp drop in the ORR performance is observed when Ir-clusters and Ir nanoparticles are decorated on the Co-oxide-supported Pd nanoparticles.