High Coverage Sub-Nano Iridium Cluster on Core-Shell Cobalt-Cerium Bimetallic Oxide for Highly Efficient Full-pH Water Splitting

The construction of sub-nanometer cluster catalysts (<1 nm) with almost complete exposure of active atoms serves as a promising avenue for the simultaneous enhancement of atom utilization efficiency and specific activity. Herein, a core-shell cobalt-cerium bimetallic oxide protected by high coverage sub-nanometer Ir clusters (denoted as Ir cluster@CoO/CeO₂) is constructed by a confined in situ exsolution strategy. The distinctive core-shell structure endows Ir cluster@CoO/CeO₂ with enhanced intrinsic activity and high conductivity, facilitating efficient charge transfer and full-pH water splitting. The Ir cluster@CoO/CeO₂ achieves low overpotentials of 49/215, 52/390, and 54/243 mV at 10 mA cm^-2 for hydrogen evolution reaction/oxygen evolution reaction (HER/OER) in 0.5 m H₂SO₄, 1.0 m PBS, and 1.0 m KOH, respectively. The small decline in performance after 300 h of operation renders it one of the most effective catalysts for full-pH water splitting. DFT calculations indicate that oriented electron transfer (along the path from Ce to Co and then to Ir) creates an electron-rich environment for surface Ir clusters. The reconstructed interface electronic environment provides optimized intermediates adsorption/desorption energy at the Ir site (for HER) and at the Ir-Co site (for OER), thus simultaneously speeding up the HER/OER kinetics.