Tuning the Catalytic Performance of Nitrogen- and Iron-Nitrogen-Doped Mesoporous Carbons for CO2 Reduction
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2024-09-20
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This thesis systematically explores the catalytic performance of nitrogen-doped and iron-nitrogen co-doped mesoporous carbon materials for electrochemical CO2 reduction (CO2RR). It particularly examines the effects of nitrogen doping speciation, structural disorder, various pore sizes, and single iron atom incorporation on catalytic performance. First, this research compares the CO2RR performance of N-doped mesoporous carbon materials in both powder (CIC) and self-supported film (NCS). These two materials were prepared using the same process except that the CICs are powder and the NCS is tape-casted into a film. Physical characterization revealed that the N-doped carbon powders possess a more disordered carbon wall structure and more micropores than the sheets, while X-ray photoelectron spectroscopy indicates a higher content of pyridinic nitrogen in the powder (53% of the total nitrogen content). The CO2RR experiments showed that the N-doped CIC-12 exhibits the highest FECO of 97%, higher than the 50% FECO shown by the N-NCS-12, attributed to the higher pyridinic N content and more structural disorder providing more active sites. Then the effect of varying pore sizes in N-doped CIC powders was explored, comparing with another method of templating carbon synthesized via aniline pyrolysis and having 22 nm pores (AD-22), containing 6 at% graphitic nitrogen and exhibiting lower structural disorder due to the absence of NH3 etching. N-doped CIC-12, with the highest structural disorder and pyridinic nitrogen, achieved 97% FECO at -0.45 V vs. RHE, while CIC-85 and CIC-22 gave lower FECO values. AD-22, containing only graphitic nitrogen, showed no CO2RR activity, confirming the inactivity of graphitic N towards CO2RR. This part of the work resulted in a first-time structure-property-performance relationship for CO2RR at N-doped carbons. Finally, the medium-performing N-CIC-85 powder was used to introduce single iron atoms to further enhance the CO2RR performance. The Fe-NCIC-85 catalysts, synthesized at 900 °C, achieved an excellent FECO of 97% at -0.45 V vs. RHE and maintained this high selectivity for over 100 hours without any signs of loss of stability beyond that. This enhancement was attributed to single-atom iron stabilization by the nitrogen doped onto the CIC powder surface during preparation through NH3 exposure.
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Li, J. (2024). Tuning the catalytic performance of nitrogen- and iron-nitrogen-doped mesoporous carbons for CO2 reduction (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.