Boron-Functionalized Organic Framework as a High-Performance Metal-Free Catalyst for N2 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.