Carbon nitrides with a high N/C atomic ratio (>2) are expected to offer superior basicity and unique electronic properties. However, the synthesis of these nanostructures is highly challenging since many parts of the CN frameworks in the carbon nitride should be replaced with thermodynamically less stable NN frameworks as the nitrogen content increases. Thermodynamically stable C3N7 and C3N6 with an ordered mesoporous structure are synthesized at 250 and 300 °C respectively via a pyrolysis process of 5-amino-1H-tetrazole (5-ATTZ). Polymerization of the precursor to the ordered mesoporous C3N7 and C3N6 is clearly proved by X-ray and electron diffraction analyses. A combined analysis including diverse spectroscopy and FDMNES and density functional theory (DFT) calculations demonstrates that the NN bonds are stabilized in the form of tetrazine and/or triazole moieties in the C3N7 and C3N6. The ordered mesoporous C3N7 represents the better oxygen reduction reaction (ORR) performances (onset potential: 0.81 V vs reversible hydrogen electrode (RHE), electron transfer number: 3.9 at 0.5 V vs RHE) than graphitic carbon nitride (g-C3N4) and the ordered mesoporous C3N6. The study on the mechanism of ORR suggests that nitrogen atoms in the tetrazine moiety of the ordered mesoporous C3N7 act as active sites for its improved ORR activity.
Bibliographical noteFunding Information:
I.Y.K. and S.K. contributed equally to this work. This work was supported by the program of the Discovery Early Career Researcher Award (DECRA) of the Australian Research Council (ARC) (grant number DE170101069) which was supported from the Australian Nuclear Science and Technology Organisation (grant number AS172/SXR/12185). I.Y.K. acknowledges financial support from the University of Newcastle (grant number G1801056UN) for this work. S.P. acknowledges SERB-NPDF fellowship (PDF/2016/001726) and SERC, IISc for computational facility.
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- DFT calculations
- N-rich carbon nitrides
- mesoporous materials