Copper single-atoms embedded in 2D graphitic carbon nitride for the CO2 reduction

Claudio Cometto,Aldo Ugolotti,Gaetano Granozzi,Elisa Grazietti,Lidia Armelao,Cristiana Di Valentin,Gregorio Bottaro,Laura Calvillo,Alessandro Moretto

doi:10.1038/s41699-021-00243-y

Abstract

We report the study of two-dimensional graphitic carbon nitride (GCN) functionalized with copper single atoms as a catalyst for the reduction of CO2 (CO2RR). The correct GCN structure, as well as the adsorption sites and the coordination of the Cu atoms, was carefully determined by combining experimental techniques, such as X-ray diffraction, transmission electron microscopy, X-ray absorption, and X-ray photoemission spectroscopy, with DFT theoretical calculations. The CO2RR products in KHCO3 and phosphate buffer solutions were determined by rotating ring disk electrode measurements and confirmed by 1H-NMR and gas chromatography. Formate was the only liquid product obtained in bicarbonate solution, whereas only hydrogen was obtained in phosphate solution. Finally, we demonstrated that GCN is a promising substrate able to stabilize metal atoms, since the characterization of the Cu-GCN system after the electrochemical work did not show the aggregation of the copper atoms.

Highlights

The depletion of fossil fuels and the increase of the atmospheric CO2 levels encourage the continuous search for alternative energy sources and routes to transform CO2 into fuels or other valueadded chemicals, which would allow us to move the C-economy from a linear- to a cyclic-one[1,2]
Taking into account the characterization results for the Cu-graphitic carbon nitride (GCN) sample and the results reported in the literature for this kind of materials, the peak at 1.5 Å can be related to Cu coordinated to N atoms in the first shell[28,52,53], the presence of Cu−O interactions cannot be excluded; while the one at 2.4 Å could be attributed to Cu−C interactions[6]
We synthesized and carefully characterized a 2D GCN functionalized with Cu single atoms by combining experimental and theoretical techniques

Summary

Introduction

The depletion of fossil fuels and the increase of the atmospheric CO2 levels encourage the continuous search for alternative energy sources and routes to transform CO2 into fuels or other valueadded chemicals, which would allow us to move the C-economy from a linear- to a cyclic-one[1,2]. In the search for highly active, selective, and durable catalysts that will make possible the commercialization of this technology, the dispersion of single metal atoms on a substrate is taking much interest in the last years[3,4,5]. It allows controlling the nature of the active sites, which could help to improve the products selectivity, since there is no presence of different phases. These materials are often unstable and tend to aggregate into clusters/nanoparticles because of their high surface free energy, which enhances their mobility on the support surface[12,13].

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Results

Conclusion