Rational Design of Single-Atom Catalysts Stabilized within the Interlayers of Covalent Organic Frameworks for the Oxygen Evolution Reaction

Abstract

Single-atom catalysts (SACs) stabilized within covalent organic frameworks (COFs) exhibit promising potential for the oxygen evolution reaction (OER). However, despite the inherently layered architecture of 2D COFs, how interlayer coordination modulates the stability and reactivity of SACs remains unclear. Here we design a comprehensive set of transition-metal SACs in monolayer and interlayer motifs and evaluate them using density functional theory (DFT) coupled with machine-learning (ML) analysis. Interlayer configurations exhibit enhanced stability owing to strengthened metal-ligand bonding, and the Rh-Pyr(4N) interlayer site achieves an exceptionally low theoretical overpotential of 0.28 V, outperforming all screened and our previously reported M-NxOy SACs. To rationalize these trends and extract general design rules, we further trained ML models on the DFT dataset. ML reveals metal electronegativity (Eele) and the average charge of coordinating nitrogen atoms (Eval_ave) as the key descriptors governing activity, defining a design window of Eval-ave < 1.2 and Eele > 2.0 associate with low overpotentials. Metals with smaller radii and higher electronegativities favor more stable configurations. This study highlights interlayer engineering as a robust strategy for stabilizing high-performance COF-based SACs and offer electronic-structure design rules for OER catalysts.