From Structure to Functional Implications: Investigation of the Melon-Like Framework of Graphitic Carbon Nitride for Li-S Batteries.

Graphitic carbon nitride (gCN) has emerged as a promising material for sustainable energy storage applications, photocatalysis, and sensors. Despite extensive research, its precise crystallographic structure remains controversial, particularly regarding the distinction between heptazine-based and melon-like frameworks. In this study, we investigate the structural characteristics of gCN synthesized using different precursors, urea and melamine. Comprehensive characterization, including X-ray diffraction (XRD), confirms that all samples exhibit a melon-like framework with P21212 symmetry. This contradicts the widely cited but experimentally unsupported heptazine-based model. We further explore how precursor selection influences crystallinity, elemental composition, and electrochemical behavior. Additionally, density functional theory (DFT) studies are also incorporated to support the experimental findings. Notably, our study is among the first to report the electrochemical performance of gCN with a confirmed melon-like structure, highlighting the strong correlation between structural attributes and functional properties. These findings provide valuable insights into the structure-property relationships in gCN and open new avenues for its rational design and applications in energy storage and conversion technologies for metal-sulfur batteries.