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

Noble-metal-free electrocatalysts for highly efficient hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are highly demanded in energy conversion and storage techniques. The single-atom catalytic (SAC) technique emerged as a promising strategy to reach this goal but is currently facing obstacles such as migration and aggregation of active atoms and low metal loading. We demonstrated from first principles that the two-dimensional (2D) covalent organic frameworks (COFs) of phthalocyanines and pyrazine linkages can firmly anchor transition-metal (TM) atoms. The resultant TM-embedded COFs (TM-COFs) exhibit multifunctional electrocatalytic activity for HER, OER, and ORR, which can be attributed to the synergistic effect of the anchored TM atoms and COFs. Specifically, Mn- and Cr-COFs are predicted to have extremely low overpotentials of −0.014/0.44/0.31 and −0.239/0.35/0.29 V for HER/OER/ORR, which are comparable or even superior to those of the well-developed noble catalysts. We also proposed the electron transfer Δδ from TM atom to the framework and p-band center εp of carbon atoms as descriptors for the adsorption strength of intermediates on the TM-COF monolayers. In view of the recent experimental progress on the synthesis of the TM-COFs, these computational results offer not only economical alternatives of noble catalysts but also a promising strategy for the design of multifunctional electrocatalysts.