Development of Crystalline Covalent Triazine Frameworks to Enable in Situ Preparation of Single-Atom Ni-N₃-C for Efficient Electrochemical CO₂Reduction

The synthesis of highly crystalline covalent triazine frameworks (CTFs) with fully conjugated nitrogen-enriched architectures is a long-term challenging subject. Herein, a solvent- and catalyst-free approach was implemented for the first time to create crystalline CTFs based on a new trimerization of amidine-type monomers. A highly crystalline triazine-linked polymer with a specific surface area of 255 m2 g-1 was achieved, whereas additional aldehydes were no longer required. Furthermore, an in situ transformation strategy was developed by exploring a molten salt (ZnCl2) to promote this new condensation, so as to convert as-obtained CTFs into isolated single-atom catalysts (SACs). Interestingly, the usage of ZnCl2 not only enables a crystalline CTF with a significantly enhanced surface area, up to 663 m2 g-1 but also provides a means of realizing atomically dispersed nickel (Ni) catalysts with unique Ni-N3-C sites. As a result, the resulting SAC exhibits efficient electrochemical carbon dioxide (CO2) reduction performance, where a maximum Faradaic efficiency for carbon monoxide (CO) production of 97.5% at -0.52 V (vs. reversible hydrogen electrode, RHE) and an excellent turnover frequency (3192 h-1) with a current density of 23.32 mA cm-2 at -1.02 V can be obtained, respectively. We anticipate our findings will facilitate new possibilities for the development of crystalline porous organic frameworks and SACs for various catalysis.