Ag Nanoparticles-Confined\nDoped within Triazine-Based\nCovalent Organic Frameworks for Syngas Production from Electrocatalytic\nReduction of CO<sub>2</sub>

Electrocatalytic CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) emerges as a promising avenue to mitigate carbon emissions,\nenabling\nthe capture and conversion of CO<sub>2</sub> into high-value products\nsuch as syngas with CO/H<sub>2</sub>. One of the crucial aspects lies\nin the tailored development of durable and efficient electrocatalysts\nfor the CO<sub>2</sub>RR. Covalent organic frameworks (COFs) possess\nunique characteristics that render them attractive candidates for\ncatalytic applications. However, the relationship between structure\nand performance still requires further exploration; especially, most\nCOFs with such properties are limited to COFs containing specific\ngroups such as phthalocyanine or porphyrin groups. Here, we custom-synthesize\ntwo azine-linked nitrogen-rich COFs constructed from triazine building\nblocks, which are doped with ultrafine and highly dispersed Ag nanoparticles\n(Ag@TFPT-HZ and Ag@TPT-HZ). Thus-obtained COFs can serve as electrocatalysts\nfor the CO<sub>2</sub>RR, and a comprehensive investigation has been\nconducted to uncover the intricate structure-performance relationship\nwithin these materials. Notably, Ag@TFPT-HZ exhibits superior CO selectivity\nin the electrocatalytic CO<sub>2</sub>RR, achieving a FE<sub>CO</sub> of 81% and a partial current density of 7.65 mA·cm<sup>–2</sup> at the potential of −1.0 V (vs reversible hydrogen electrode\n(RHE)). In addition, Ag@TPT-HZ as an electrocatalyst can continuously\nproduce syngas with a CO/H<sub>2</sub> molar ratio of 1:1, an ideal\ncondition for methanol synthesis. The observed distinct performance\nbetween these two COFs is attributed to the presence of O atoms in\nTFPT-HZ. These O atoms facilitate a higher loading capacity of Ag\nnanoparticles (11 wt %) and generate a greater number of active sites,\nthereby enhancing electrochemical activity and promoting faster reaction\nkinetics. Therefore, two tailor-made two-dimensional (2D) nitrogen-rich\nCOFs with various active sites as electrocatalysts can exhibit different\noutstanding electrocatalytic performances for CO<sub>2</sub>RR and\npossess high cycling stability (>50 h). This work offers valuable\ninsights into the design and synthesis of electrocatalysts, particularly\nin elucidating the intricate relationship between their structure\nand performance.