Two-dimensional conjugated metal–organic frameworks TM3(HAT)2: a new family of promising single-atom electrocatalysts for efficient nitrogen fixation

Abstract

Achieving efficient nitrogen reduction reaction (NRR) under mild conditions is desirable but still challenging due to the lack of high-performance catalysts. Herein, we report the feasibility of a new type of two-dimensional conjugated metal–organic frameworks (cMOFs) featuring dense single-metal-atom sites, namely TM3(HAT)2 monolayers (TM = transition metal from groups 4 to 10, HAT = 1,4,5,8,9,12-hexaazatriphenylene), as NRR catalysts. We construct an efficient four-step screening strategy and identify the W3(HAT)2 monolayer as a candidate with considerable stability, activity, and selectivity based on density functional theory (DFT) computations. The analysis of bonding, integrated-crystal orbital Hamilton population, and Bader charge uncovers the NRR activity origin of the TM3(HAT)2 monolayers and elucidates the structure–performance correlations. Meanwhile, our results show that a simple descriptor ϕ based on the inherent nature of the TM atoms can be applied to accelerate the screening of candidates without explicit DFT calculations. This work highlights a feasible strategy to prescreen and design high-performance cMOF-based electrocatalysts.