Ag Nanoparticles-Confined Doped within Triazine-Based Covalent Organic Frameworks for Syngas Production from Electrocatalytic Reduction of CO₂

Electrocatalytic CO₂ reduction reaction (CO₂RR) emerges as a promising avenue to mitigate carbon emissions, enabling the capture and conversion of CO₂ into high-value products such as syngas with CO/H₂. One of the crucial aspects lies in the tailored development of durable and efficient electrocatalysts for the CO₂RR. Covalent organic frameworks (COFs) possess unique characteristics that render them attractive candidates for catalytic applications. However, the relationship between structure and performance still requires further exploration; especially, most COFs with such properties are limited to COFs containing specific groups such as phthalocyanine or porphyrin groups. Here, we custom-synthesize two azine-linked nitrogen-rich COFs constructed from triazine building blocks, which are doped with ultrafine and highly dispersed Ag nanoparticles (Ag@TFPT-HZ and Ag@TPT-HZ). Thus-obtained COFs can serve as electrocatalysts for the CO₂RR, and a comprehensive investigation has been conducted to uncover the intricate structure-performance relationship within these materials. Notably, Ag@TFPT-HZ exhibits superior CO selectivity in the electrocatalytic CO₂RR, achieving a FE_CO of 81% and a partial current density of 7.65 mA·cm^-2 at the potential of -1.0 V (vs reversible hydrogen electrode (RHE)). In addition, Ag@TPT-HZ as an electrocatalyst can continuously produce syngas with a CO/H₂ molar ratio of 1:1, an ideal condition for methanol synthesis. The observed distinct performance between these two COFs is attributed to the presence of O atoms in TFPT-HZ. These O atoms facilitate a higher loading capacity of Ag nanoparticles (11 wt %) and generate a greater number of active sites, thereby enhancing electrochemical activity and promoting faster reaction kinetics. Therefore, two tailor-made two-dimensional (2D) nitrogen-rich COFs with various active sites as electrocatalysts can exhibit different outstanding electrocatalytic performances for CO₂RR and possess high cycling stability (>50 h). This work offers valuable insights into the design and synthesis of electrocatalysts, particularly in elucidating the intricate relationship between their structure and performance.