Two-dimensional AlN/g-CNs van der Waals type-II heterojunction for water splitting

A type-II van der Waals heterojunction photocatalyst is not only an ideal material for hydrogen production by water splitting, but also an important way to improve efficiency and produce low-cost clean energy. In this work, we unexpectedly found that monolayers of AlN and C2N, g-C3N4, and C6N8 all formed type-II heterojunctions according to density functional theory, and we report a comparison of their photocatalytic performance. Among them, the AlN/C2N heterojunction has an appropriate band gap value of 1.61 eV for visible light water splitting. It has higher carrier mobility than the AlN/g-C3N4 heterojunction (electron 253.1 cm(2) V-1 s(-1) > 31.6 cm(2) V-1 s(-1) and hole 11043.4 cm(2) V-1 s(-1) > 524.7 cm(2) V-1 s(-1)), and an absorption peak similar those of monolayer C2N in visible light (8 x 10(4) cm(-1)) and monolayer AlN in ultraviolet light (11 x 10(4) cm(-1)). The Bader charge shows that the charge transfer number of the AlN/g-C3N4 heterojunction is higher than that of the AlN/C2N heterojunction, and its Gibbs free energy (-0.22 eV) is smaller than that of single-layer g-C3N4 (-0.30 eV). The AlN/C6N8 heterojunction also has a perfect band gap of 2.16 eV and an absorption peak of over 10 x 10(4) cm(-1) in the UV region. Since a type-II heterojunction can effectively promote the separation of photogenerated electron-hole pairs and prevent their rapid recombination, the above heterojunctions are promising candidates for new photocatalysts.

Automated summary

Based on density functional theory, this study unexpectedly found that monolayers of AlN and C2N, g-C3N4, and C6N8 all formed type-II heterojunctions, which showed promising potential in photocatalytic applications. The AlN/C2N heterojunction demonstrated an appropriate band gap value for visible light water splitting and higher carrier mobility compared to other heterojunctions.