Stable Multifunctional Single-Atom Catalysts Resulting\nfrom the Synergistic Effect of Anchored Transition-Metal Atoms and\nHost Covalent–Organic Frameworks

Abstract

Noble-metal-free\nelectrocatalysts for highly efficient hydrogen\nevolution reaction (HER), oxygen evolution reaction (OER), and oxygen\nreduction reaction (ORR) are highly demanded in energy conversion\nand storage techniques. The single-atom catalytic (SAC) technique\nemerged as a promising strategy to reach this goal but is currently\nfacing obstacles such as migration and aggregation of active atoms\nand low metal loading. We demonstrated from first principles that\nthe two-dimensional (2D) covalent organic frameworks (COFs) of phthalocyanines\nand pyrazine linkages can firmly anchor transition-metal (TM) atoms.\nThe resultant TM-embedded COFs (TM-COFs) exhibit multifunctional electrocatalytic\nactivity for HER, OER, and ORR, which can be attributed to the synergistic\neffect of the anchored TM atoms and COFs. Specifically, Mn- and Cr-COFs\nare predicted to have extremely low overpotentials of −0.014/0.44/0.31\nand −0.239/0.35/0.29 V for HER/OER/ORR, which are comparable\nor even superior to those of the well-developed noble catalysts. We\nalso proposed the electron transfer Δδ from TM atom to\nthe framework and p-band center ε_p of carbon atoms\nas descriptors for the adsorption strength of intermediates on the\nTM-COF monolayers. In view of the recent experimental progress on\nthe synthesis of the TM-COFs, these computational results offer not\nonly economical alternatives of noble catalysts but also a promising\nstrategy for the design of multifunctional electrocatalysts.