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

Abstract

Abstract A ternary catalyst comprising Iridium (Ir) single‐atoms (SA)s decorated on the Co‐oxide supported palladium (Pd) nanoparticles (denoted as CPI‐SA) is developed in this work. The CPI‐SA with 1 wt.% of Ir exhibits unprecedented high mass activity (MA) of 7173 and 770 mA mgIr−1, respectively, at 0.85 and 0.90 V versus RHE in alkaline ORR (0.1 m KOH), outperforming the commercial Johnson Matthey Pt catalyst (J.M.‐Pt/C; 20 wt.% 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 13 342 and 1372 mA mgIr−1, respectively, at 0.85 and 0.90 V versus RHE up to 69 000 cycles (3 months) in the accelerated degradation test (ADT). Evidence from the in situ partial fluorescence yield X‐ray absorption spectroscopy (PFY‐XAS) and the electrochemical analysis indicate that the Ir single‐atoms and adjacent Pd domains synergistically promote the O2 splitting and subsequent desorption of hydroxide ions (OH−), respectively. Whereas the Co‐atoms underneath serve as electron injectors to boost the ORR activity of the Ir single‐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.

Keywords

• fuel cells
• in situ PFY XAS
• mass activity
• oxygen reduction reaction
• single atoms