Importing Antibonding-Orbital Occupancy through Pd-O-Gd Bridge Promotes Electrocatalytic Oxygen Reduction

The active-site density, intrinsic activity, and durability of Pd-based materials for oxygen reduction reaction (ORR) are critical to their application in industrial energy devices. This work constructs a series of carbon-based rare-earth (RE) oxides (Gd2O3, Sm2O3, Eu2O3, and CeO2) by using RE metal-organic frameworks to tune the ORR performance of the Pd sites through the Pd-RExOy interface interaction. Taking Pd-Gd2O3/C as a representative, it is identified that the strong coupling between Pd and Gd2O3 induces the formation of the Pd-O-Gd bridge, which triggers charge redistribution of Pd and Gd2O3. The screened Pd-Gd2O3/C exhibits impressive ORR performance with high onset potential (0.986 VRHE), half-wave potential (0.877 VRHE), and excellent stability. Similar ORR results are also found for Pd-Sm2O3/C, Pd-Eu2O3/C, and Pd-CeO2/C catalysts. Theoretical analyses reveal that the coupling between Pd and Gd2O3 promotes electron transfer through the Pd-O-Gd bridge, which induces the antibonding-orbital occupancy of Pd-*OH for the optimization of *OH adsorption in the rate-determining step of ORR. The pH-dependent microkinetic modeling shows that Pd-Gd2O3 is close to the theoretical optimal activity for ORR, outperforming Pt under the same conditions. By its ascendancy in ORR, the Pd-Gd2O3/C exhibits superior performance in Zn-air battery as an air cathode, implying its excellent practicability. This work constructs a series of carbon-based rare-earth oxides via an RE metal-organic framework-mediated strategy to tune the ORR performance of the Pd sites. Taking Pd-Gd2O3/C as a representative, it is identified that the coupling between Pd and Gd2O3 promotes electron transfer through the Pd-O-Gd bridge, which induces the antibonding-orbital occupancy of Pd-*OH for the optimization of *OH adsorption in the rate-determining step of ORR.+image