Covalent Organic Framework: An Emerging Catalyst for Renewable Ammonia Production

Abstract

Ammonia (NH3), a fertilizer feedstock and clean energy carrier, is produced primarily by the Haber-Bosch method, which is environmentally hazardous and energy intensive. Therefore, there is an immediate need for a benign alternative, like catalytic nitrogen fixation, such as catalytic nitrogen reduction reaction (NRR). NRR must involve active, selective, scalable, and long-lived catalysts to become a sustainable source of ammonia production. Recently, covalent organic frameworks (COFs) and COF-based functional materials have been proposed as promising catalysts for NRR. COFs comprise repeating units of organic molecules connected by strong covalent bonds. By fine-tuning the building blocks, various COFs can be designed with numerous active sites. This class of materials offers excellent modularity, porosity, stability, and low density. A novel type of nitrogen-abundant COFs called covalent triazine framework (CTF) has been noted for its high electron density and ultra-stability. This review examines the state-of-the-art for the NRR using different COF-based catalysts and discusses design principles for advancing it. The underlying mechanism of NRR with different strategies adopted for renewable ammonia production is also discussed for a clear understanding of the process. Furthermore, key parameters for improving ammonia synthesis‘s photo/electrocatalytic efficiency will also be highlighted to present new possibilities to this emerging field.