Atomically Engineered Defect-Rich Palladium Metallene for High-Performance Alkaline Oxygen Reduction Electrocatalysis

Defect engineering is a key chemical tool to modulate the electronic structure and reactivity of nanostructured catalysts. Here, it is reported how targeted introduction of defect sites in a 2D palladium metallene nanostructure results in a highly active catalyst for the alkaline oxygen reduction reaction (ORR). A defect-rich WO_x and MoO_x modified Pd metallene (denoted: D-Pd M) is synthesized by a facile and scalable approach. Detailed structural analyses reveal the presence of three distinct atomic-level defects, that are pores, concave surfaces, and surface-anchored individual WO_x and MoO_x sites. Mechanistic studies reveal that these defects result in excellent catalytic ORR activity (half-wave potential 0.93 V vs. RHE, mass activity 1.3 A mgPd^-1 at 0.9 V vs. RHE), outperforming the commercial references Pt/C and Pd/C by factors of ≈7 and ≈4, respectively. The practical usage of the compound is demonstrated by integration into a custom-built Zn-air battery. At low D-Pd M loading (26 µgPd cm^-2), the system achieves high specific capacity (809 mAh g_Zn ^-1) and shows excellent discharge potential stability. This study therefore provides a blueprint for the molecular design of defect sites in 2D metallene nanostructures for advanced energy technology applications.