Chemically heterogeneous nitrogen sites of various reactivity in porous carbons provide high stability of CO2 electroreduction catalysts

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Applied Catalysis B: Environmental


Microporous carbons of high nitrogen-content and diverse nitrogen-doping sites were studied for CO2 electrochemical reduction. The unique feature of these carbon materials is the presence of chemically heterogeneous nitrogen species of various reactivity. The systematic surface chemistry study reveals that some nitrogen moiety, even though it has no direct catalytic role in the CO formation during CO2 reduction process, protects the active pyridinic nitrogen from oxidation. In that protection mechanism, these species, instead of pyridines, are oxidized. Therefore, that nitrogen is believed to be responsible for the exceptional stability of the carbon catalysts found in this study. Besides CO and CH4, methanol, formic acid and C3 hydrocarbons (acetone and propanol) were also detected as reduction products. C3 hydrocarbons are the first reported products among the metal-free catalysts for CO2 reduction. The results suggest that the C3 products could be formed when more than one nitrogen sites are located close to each other in the pore space. Furthermore, the differences in the porosity suggest that the microporous structure of the carbons favors the hydrocarbons formation. Eventually, the carbons described herein offer a unique combination of chemical and physical properties, which give further insights into the electrochemical reduction of CO2 on functional carbon materials.