Development of Crystalline Covalent Triazine Frameworks to Enable In Situ Preparation of Single-Atom Ni-N3-C for Efficient Electrochemical CO2 Reduction

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 m(2) 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 m(2) g(-1) but also provides a means of realizing atomically dispersed nickel (Ni) catalysts with unique Ni-N-3-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.

Automated summary

Highly crystalline covalent triazine frameworks (CTFs) were synthesized for the first time using a solvent-and catalyst-free approach. The CTFs were then transformed into isolated single-atom catalysts (SACs) through a new condensation reaction. These SACs exhibited efficient performance in electrochemical carbon dioxide reduction.