Heptazine-based porous graphitic carbon nitride: a visible-light driven photocatalyst for water splitting

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 7; no. 36; pp. 2799 - 285
• Main Authors: Liu, Bin, Xu, Bo, Li, Shenchang, Du, Jinli, Liu, Zhiguo, Zhong, Wenying
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 2019
• Subjects: Carbon; Carbon nitride; Chemical reduction; Density functional theory; Electron mobility; Electronics industry; Energy conversion; Energy conversion efficiency; Energy gap; Free energy; Hole mobility; Mobility; Monolayers; Oxidation; Photocatalysts; Redox reactions; Splitting; Water splitting
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c9ta03646f

Graphitic carbon nitride (C 3 N 4 ) based semiconductors are found to be potential metal-free photocatalysts for water splitting. However, due to the wide band gap, C 3 N 4 has insufficient sunlight absorption which limits the energy conversion efficiency. Here, by means of density functional theory, we explore a heptazine-based porous graphitic carbon nitride, the C 6 N 7 monolayer as a visible-light driven photocatalyst for water splitting. The C 6 N 7 monolayer possesses a direct band gap of 1.90 eV and pronounced optical absorbance in the visible light region. More importantly, the band alignment of the C 6 N 7 monolayer with respect to the water redox levels is found to satisfy the thermodynamic criteria for water splitting. By evaluating the free energy change in the oxidation/reduction reactions of the C 6 N 7 monolayer, it is found that cocatalysts are required for water splitting. The C 6 N 7 monolayer also favours separation of photoexcited electron-hole pairs, due to its high electron mobility (∼10 4 cm 2 V −1 s −1 ) but very low hole mobility, which renders the C 6 N 7 monolayer a promising candidate for water splitting under visible light. Heptazine-based porous graphitic carbon nitride with a suitable band alignment with respect to the water redox levels for water splitting.