Renewable electricity powered reduction of carbon dioxide (CO₂) to fuels and chemicals has extensive potential to close the anthropogenic carbon cycle. Methane (CH₄) which is one of the kinetically hindered high electron reduction product in the electrochemical CO₂ conversion pathway can be used not only as fuel but also as a hydrogen carrier. Thus, CH₄ production via CO₂ electroreduction has received considerable attention in the past few years for use in supporting carbon capture and utilization.^1,2 The design of active and selective electrocatalysts with extraordinary CO₂-to-CH₄ conversion efficiency is highly desirable but still very challenging. Amine functionalization as a general strategy, can be adapted to the nanoscale carbon electrocatalysts i.e., in the form of GQDs irrespective of its crystal structure, to promote the selectivity and production rate of CH₄ in CO₂ electro-reduction. In this work, we present a molecular tuning strategy- in-situ amine functionalization of nitrogen-doped graphene quantum dots (N-GQDs) for CO₂-to-CH₄ conversion at high efficiencies.³ N- GQDs achieve a CH₄ Faradic efficiency (FE) of 63% and 46%, respectively, at CH₄ partial current densities of 170 and 258 mA cm^-2, matching to or even surpassing the performance of the state-of-the-art Cu-based catalysts.^4,5 The N-GQDs also produce C₂ products comprising primarily ethylene (C₂H₄) and ethanol (C₂H₅OH) with a maximum FE of ~10%. Detailed structure-activity relationship studies reveal that the CH₄ yield varies linearly with amine group content, whereas the C₂ production rate shows a positive dependence on the pyridinic N dopant content. This work provides valuable insights into the rational design of carbon nano-catalysts with CO₂-to-CH₄ conversion efficiency at the industrially relevant level.

References:

(1) Bushuyev, O. S.; De Luna, P.; Dinh, C. T.; Tao, L.; Saur, G.; van de Lagemaat, J.; Kelley, S. O.; Sargent, E. H. What Should We Make with CO2 and How Can We Make It? Joule 2018, 2 (5), 825–832. https://doi.org/10.1016/j.joule.2017.09.003.

(2) Nitopi, S.; Bertheussen, E.; Scott, S. B.; Liu, X.; Engstfeld, A. K.; Horch, S.; Seger, B.; Stephens, I. E. L.; Chan, K.; Hahn, C.; Nørskov, J. K.; Jaramillo, T. F.; Chorkendorff, I. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Chem. Rev. 2019, 119 (12), 7610–7672. https://doi.org/10.1021/acs.chemrev.8b00705.

(3) Amine‐Functionalized Carbon Nanodot Electrocatalysts Converting Carbon Dioxide to Methane - Yadav - - Advanced Materials - Wiley Online Library https://onlinelibrary.wiley.com/doi/10.1002/adma.202105690 (accessed 2021 -12 -20).

(4) Cai, Y.; Fu, J.; Zhou, Y.; Chang, Y.-C.; Min, Q.; Zhu, J.-J.; Lin, Y.; Zhu, W. Insights on Forming N,O-Coordinated Cu Single-Atom Catalysts for Electrochemical Reduction CO2 to Methane. Nat. Commun. 2021, 12 (1), 586. https://doi.org/10.1038/s41467-020-20769-x.

(5) Chang, C.-J.; Lin, S.-C.; Chen, H.-C.; Wang, J.; Zheng, K. J.; Zhu, Y.; Chen, H. M. Dynamic Reoxidation/Reduction-Driven Atomic Interdiffusion for Highly Selective CO2 Reduction toward Methane. J. Am. Chem. Soc. 2020, 142 (28), 12119–12132. https://doi.org/10.1021/jacs.0c01859.