LAUSR

Moderate adsorption of oxygenated intermediates takes a significant role in rational design of high‐efficiency oxygen reduction reaction (ORR) electrocatalysts. Long‐serving as a reliable strategy to tune geometric structure of nanomaterials, defect engineering enjoys the great ability of adjusting the coordination environment of catalytic active sites, which enables dominant regulation of adsorption energy and kinetics of ORR catalysis. However, limited to controllable nanocrystals fabrication, inducing uniformly dispersed high‐coordinated defects into ultrathin 2D nanosheets remains challenging. Herein, atomic‐scale cavities (ASCs) are proposed as a new kind of high‐coordinated active site and successfully introduced into suprathin Pd (111)‐exposed metallene. Due to its atomic concave architecture, leading to elevated CN and moderately downshifted d‐band center, the as‐made Pd metallene with ASCs (c‐Pd M) exhibits excellent ORR performance with mass activity of 2.76 A mgPd−1 at 0.9 V versus reversible hydrogen electrode (RHE) and half‐wave potential as high as 0.947 V, which is 18.9 (2.7) times higher and 104 (46) mV larger than that of commercial Pt/C (Pd metallene without ASCs). Besides, the durability of c‐Pd M exceeds its commercial counterpart with ≈30% loss after 5000 cycles. This work highlights a new‐style mentality of designing fancy active sites toward efficient ORR electrocatalysis.