Strain Engineering of 2D-C<sub>3</sub>N<sub>5</sub> Monolayer and Its Application in Overall Water-Splitting: a Hybrid Density Functional Study
Shakti Singh, P. Anees, Sharat Chandra, Tapan K. Ghanty
Abstract
The recent experimental synthesis of 2D graphitic C3N5 has attracted a lot of interest in its electronic and optical properties and its comparison with other graphitic C3N4 and C3N3. To this end, we performed density functional theory calculations using the accurate HSE06 functional and estimated the corresponding electronic properties. From a comparative study of the band structures of C3N3, C3N4, and C3N5, we found that the electronic band gap decreases in the order 3.24 eV (C3N3) > 2.81 eV (C3N4) > 2.19 eV (C3N5) with an increase in the number of nitrogen atoms in the unit cell of these graphitic carbon nitrides. Further, the strain dependency of the band structure of 2D g-C3N5 under uniaxial and biaxial strains is performed using the same HSE-06 functional. We found a systematic decrease of band gap as strain increases. Out of the two types of strains, the biaxial strain has been found to be more efficient in modulating the band gap. The effect of strain on the structure is also explored by analyzing the bond lengths and bond angles as well as the charge density plots. Furthermore, we found that at a biaxial strain of 20%, an interesting structural rearrangement occurs in 2D g-C3N5, which results in a finite magnetic moment arising from the loss of spin-degeneracy of electronic levels. Finally, by studying the evolution of band gap, band alignments, and optical absorption as a function of strain, we are able to predict that C3N5 with biaxial strain in the range of 12–14% can be a promising photocatalyst in overall water-splitting with excellent optical absorption in the visible light spectrum.