Tracing the Structure-Activity Correlation in Cobalt-Doped Heteroatom-Enriched Nanoporous Material for CO2 Electroreduction
Authors: Sharma Ruchi , Gammelgaard Jens Jakob , Frank Sara , Lock Nina 
Published: December 2024

The electrochemical CO2 reduction reaction (CO2RR) to value added chemicals (CO, HCOOH, CH4, CH3OH, C2H5OH etc.) utilizing renewable energy sources has attracted considerable attention to close carbon cycle. [1,2] It has several advantages over other approaches such as 1) CO2 could be reduced under mild temperature and pressure conditions, 2) process could be controlled by adjusting the various reaction parameters such as potential etc., and 3) process is compact and feasible for scale up application. [1-3] However, this process has some limitations such as high overpotential, low selectivity & faradaic efficiency for products. Therefore, the designing of highly active electrocatalysts is required to improve catalytic efficiency. Among various reported catalysts, cobalt doped nitrogen enriched materials with atomically dispersed Co–N sites have displayed superior activities and selectivity in electrochemical process for the reduction of CO2. [1-4] However, the effect of synthesis conditions and composition of active species on product selectivity is not rigorously studied yet.
In this research, a series of Co-doped multifunctional nitrogen-enriched nanoporous polymer (n-Co@MNENP) with amine and hydroxyl functionalities has been synthesized by condensation of 2-hydroxy-1,3,5-benzenetricarbaldehyde and melamine with calculated amount of cobalt chloride hexahydrate for incorporating n% (n = 10, 50 and 100) of Co content followed by pyrolysis at temperature 550 (designated as n-Co@MNENP-550) and 700 °C (designated as n-Co@MNENP-700). The structure of the synthesized in-situ and pyrolyzed specimens was confirmed by spectroscopic investigations such as FT-IR, and XPS. The Co content was estimated from ICP analysis. The thermal stability of the specimen was investigated using TGA/DTG. The FE-SEM and EDAX revealed almost spherical agglomerated nanoparticles with homogeneous distribution of Co species. PDF and total scattering (TS) analysis confirmed the presence of Co-N species in 10% and 100% samples while 50% sample has metallic Co(fcc/hcp) and CoO/N active species. Further, synthesized specimens have been explored for CO2RR. Among all the electrocatalysts, n-Co@MNENP-700 have shown the higher activity in CO2RR in which 10-Co@MNENP-700 and 100-Co@MNENP-700 could only produce CO, while 50-Co@MNENP-700 results in CO and C2H5OH production. These results reveal that atomically dispersed cobalt–nitrogen sites are responsible for CO generation while CoO, metallic Co species in combination with Co-N sites are responsible for CO and C2H5OH generation which confirmed that the compositions of Co-based catalysts greatly influence CO2RR activity and selectivity.

References

[1] M. Usman, M. Humayun, M. D. Garba, L. Ullah, Z. Zeb, A. Helal, M. H. Suliman, B. Y. Alfaifi, N. Iqbal, M. Abdinejad, A. A. Tahir, Nanomaterials
2021, 11, 2029.
[2] K. Iwase et al. ACS Appl. Mater. Interfaces
2021, 13, 15122-15131.
[3] W. Ju et al. Nat. commun.
2017, 8, 944.
[4] J. Chen et al. J. Phys. Chem. C
2020, 124, 16501-16507.