Augmenting mesopores can enhance the accessibility of active sites and facilitate the mass transport of eCO2RR-relevant intermediates. Mesopore augmentation can surpass the atomic-scale modulation of the active sites, demonstrating superior activity compared to nonporous counterparts. Also, creating abundant porosity in catalysts can suppress the HER by influencing the local alkalinity near the active sites. For instance, accumulating hydroxide ions at the interface between the catalyst and the electrolyte (CO2 + H2O + 2e− → CO + 2OH−) during eCO2RR limits the competing HER.
Nevertheless, the advancement of mesopore construction strategies in N-C materials still faces significant challenges in establishing the performance-structure relationship. This challenge stems from the fact that introducing mesopores usually alters the active sites or the chemical composition of the catalysts, adding further complexity to the investigation of porosity-induced performance in N-C materials. As a result, the interaction between porosity modifications and variations in active sites complicates understanding the performance-structure correlation in N-C materials. Evidently, maintaining consistency in the types of active sites and their immediate surroundings would facilitate a clearer understanding of the contribution of distinct pore types to the conversion of CO2 to CO. The aim of our study is to isolate the augmented porosity from other alterations in the catalysts' composition, allowing the impact of increased mesopore content in N-C materials to be studied on both the selectivity and activity of eCO2RR.
I present a strategy for enhancing the mesopore content in N-C materials derived from metal-organic frameworks (MOFs) by incorporating additional carbon sources to improve the catalytic performance of eCO2RR. Specifically, we used isoreticular MOF (i.e. IRMOF 3), with a pore size diameter of 1.5 nm, as the precursor for the carbon matrix. To prevent structural collapse and preserve porosity during the subsequent carbonization process, N-rich monomers containing O [furfuryl alcohol (FA)], known for its polycondensation properties, was introduced into the IRMOF-3 cavities through nanocasting as an additional carbon source, creating the FA-IRMOF-3 composite material. Therefore, after pyrolysis, we successfully designed two N-C catalyst materials featuring varying mesopore content with an average pore size of ~10 nm. The careful nanocasting process preserved the types and content of active sites and the size of catalysts, selectively enhancing the mesopore content in the resulting N-C catalyst (referred to as P-N-C). As a result, the P-N-C material continuously maintained a high FECO (>90%) and outperformed N-C and P-O-C across the entire potential window. Meanwhile, this substrate provides a large-surface-area substrate for the next SAC loading.
