Unraveling the fundamental determinants of the intrinsic activity of practical catalysts has long been challenging, mainly due to the complexity of the structures and surfaces of such catalysts. Current understandings of intrinsic activity mostly come from model catalysts. Here, a pH-induced ligand adsorption strategy is developed to achieve controllable synthesis of self-assembled low-dimensional PdMo nanostructures, including 1D nanowires, 2D metallenes, and 2D metallene nanoveins. A strong correlation is established between the intrinsic oxygen reduction reaction (ORR) activity and the density of grain boundaries. Increased grain boundary density induces more extensive tensile strain, which, in synergy with electronic interactions within PdMo alloys, effectively lowers the energy barrier of the rate-determining step (*O to *OH). 2D PdMo metallene nanoveins, featuring the highest grain boundary density and a unique mesoporous structure, exhibit superior ORR activity and mass transport capabilities. Computational fluid dynamics simulations and in situ spectroscopy are employed to elucidate the structure-activity relationship. This work provides fundamental insights into the critical role of grain boundary engineering in enhancing ORR electrocatalysis in Pd-based nanostructures.
Keywords: grain boundary; low‐dimensional materials; metallenes; oxygen reduction; structure‐activity relationship.
© 2025 Wiley‐VCH GmbH.