Engineering single-atom catalysts on triazine-based covalent organic frameworks for enhanced photocatalytic performance in N2 reduction

The solar conversion of nitrogen to ammonia is a green, sustainable, and promising way to fix nitrogen. However, designing a photocatalyst with high activity, selectivity, and stability for the N2 reduction reaction (NRR) is challenging because of the slow inert activation of N2 and competitive hydrogen evolution reaction (HER). Herein, a single metal site anchored to a triazine-based covalent organic framework (Tr-COF) backbone (named TM@Tr-COF; TM = Fe, Co and Ni) is fabricated for high-performance catalytic N2 reduction. Density functional theory calculations show that the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF can effectively activate N2 and reduce it to NH3 via the electron "acceptance-donation" process. Meanwhile, the NRR occurs via the enzymatic pathway on the Fe@Tr-COF, Co@Tr-COF and Ni@Tr-COF with a limiting potential of 0.38 V, 0.58 V and 0.54 V, respectively. Furthermore, the anchoring of Fe/Co/Ni on the Tr-COF allows the Tr-COF to be adjusted to the appropriate edge position and visible light-absorption region, indicating that the system may be a promising and efficient photocatalyst. Compared with other competitive reactions, the system exhibits high selectivity for NH3 production and inhibits competitive HERs. These findings have considerable implications for innovatively designing highly active single-atom catalysts supported by COFs.