Oriented Assembly of Boundary‐Engineered Heterojunctions via Cerium Single‐Atom Doping for Enhanced Oxygen Evolution

Abstract The oriented assembly of heterostructures at the boundaries of nanosheets offers substantial advantages over surface‐based heterostructures, owing to their enhanced built‐in electric fields, more efficient charge transport pathways, and greater accessibility of active sites. However, the precise design of boundary‐engineered heterojunctions remains challenging due to the complex process and unclear growth mechanism. Herein, the development of a boundary‐engineered heterojunction is reported by loading Ce‐Ni(OH) 2 onto the edges of Co‐MOF nanosheets through a regulated electrodeposition process, driven by boundary effect induced by Ce single‐atom doping. A systematic investigation is conducted to explore the effects of boundary effect on the construction of boundary‐engineered heterojunctions. The Co‐MOF/Ce‐Ni(OH) 2 @CC exhibits superior oxygen evolution reaction (OER) activity, achieving an ultra‐low overpotential of 140 mV at 10 mA cm −2 in 1 M KOH. Enhanced by density functional theory (DFT) calculations and in situ Raman characterization, the Ce single‐atom acts as an electron reservoir for Ni sites via the Ce─O─Ni chain during OER, thereby facilitating electron transfer from Ni(OH) 2 to Co‐MOF. This promotes the formation of NiOOH and boosts the OER activity. Furthermore, the Kelvin probe force microscopy (KPFM) analysis reveals that the incorporation of Ce intensifies the local electric field at the nanosheet boundary, and facilitates the deposition of Ni(OH) 2 on the edges, thereby promoting the formation of boundary‐engineered heterojunctions.