Structure-property-performance relationship of a series of CO₂RR-active N-doped mesoporous carbon frameworks

Abstract

While electrochemical CO₂ reduction (CO₂RR) enables the sustainable conversion of CO₂ to value-added products, the design of efficient, selective, and earth-abundant catalysts remains challenging. Metal catalysts, commonly used for aqueous CO₂RR, can exhibit limited selectivity, instability, and high cost, thus hindering large-scale implementation. In contrast, heteroatom-doped (e.g., nitrogen) carbons that selectively convert CO₂ to CO are emerging as possible alternatives. However, the relationship between the nitrogen content and functionalities, the carbon support properties, and the CO₂RR performance, remains unclear, due in large part to the significant variations in the carbon materials employed to date. To address this, we systematically investigated a series of ordered, silica colloid-imprinted mesoporous carbon powders with highly reproducible and tunable pore sizes, known nitrogen speciation, and varying degrees of carbon crystallinity on the CO₂RR selectivity and activity. The results show that CO selectivity is mainly governed by the presence of structural disorder in the carbon framework as well as by a rich density of pyridinic nitrogen surface sites, with the best performing N-C catalyst exhibiting an exceptional CO Faradaic efficiency of 97%. DFT calculations were also conducted, confirming that pyridinic-N sites offer the most favorable binding for CO₂ intermediates during CO production, supporting the superior CO₂RR activity observed experimentally. It is also shown that the CO₂RR activity correlates with nitrogen content and accessible surface area, showing an onset overpotential of only -240 mV. These insights reveal some key structure-property-performance relationships that govern CO₂ reduction at N-doped carbons, offering guidance especially for the design and preparation of new carbon supports with optimal properties.