Boron-Functionalized Organic Framework as a High-Performance Metal-Free Catalyst for N-2 Fixation

Inspired by the recently synthesized covalent organic framework (COF) containing triquinoxalinylene and benzoquinone units (TQBQ) in the skeleton, we study the stability and properties of its two-dimensional analogue, TQBQCOF, and examine its potential for the synthesis of ammonia using first-principles calculations. We show that the TQBQCOF sheet is mechanically, dynamically, and thermally stable up to 1200 K. It is a semiconductor with a direct band gap of 2.70 eV. We further investigate the electrocatalytic reduction of N-2 to NH3 on the Boron-functionalized TQBQCOF sheet (B/TQBQCOF). The rate-determining step of the catalytic pathways is found to be *N-N -> *N-NH for the distal, alternating, and enzymatic catalytic mechanisms, with the corresponding overpotentials of 0.65, 0.65, and 0.07 V, respectively. The value of 0.07 V is the lowest required voltage among all of the N-2 reduction catalysts reported so far, showing the potential of B/TQBQCOF as a metal-free catalyst to effectively reduce N-2 to NH3.