High-Loading Single-Atom Catalyst via On-Surface Synthesis of a Metal-Covalent Organic Framework for Oxygen Reduction Reaction

The development of active catalysts with both high metal efficiency and the use of earth-abundant metals is the ultimate goal for advancing the required commercially viable and sustainable energy conversion technologies of the future. Metal–organic frameworks (MOFs) have emerged as promising candidates due to their high surface area and tunable active sites. This study aims to fabricate a type of high metal loading single-atom catalysts (SACs) based on two-dimensional (2D) metal–organic covalent organic frameworks (MCOFs) with uniform, active, and stable Fe–N3 sites. The MCOFs were synthesized through an on-surface polymerization process using Fe and melamine as precursors. The polymerization steps were characterized by using operando high-pressure scanning tunneling microscopy (HP-STM), in situ X-ray photoelectron spectroscopy (XPS), low-temperature STM (LT-STM), and computational calculations. The synthesized MCOFs demonstrate favorable adsorption and activation of O2 at the Fe–N3 sites, which shows reactivity for electrocatalytic oxygen reduction reaction. The surface chemistry and functionality of 2D MCOFs can be rationally designed by varying the metal atoms and organic linkers, offering a versatile platform for diverse applications.