Comments on “Reduced band gap & charge recombination rate in Se doped α-Bi2O3 leads to enhanced photoelectrochemical and photocatalytic performance: Theoretical & experimental insight” [Int J Hydrogen Energy 42 (2017) 20638–20648]

In this short communication, I comment the information recently reported by Sharma et al. [1]. The aim of this short communication is to provide awareness of the phases of the Bi₂O₃ between the audiences of International Journal of Hydrogen Energy. Based upon the perspective of numerous reports worldwide, I attract audiences' attention to the reality that Bi₂O₃ has six phases' polymorphs.     

Favourable band edge alignment and increased visible light absorption in β-MoO3/α-MoO3 oxide heterojunction for enhanced photoelectrochemical performance

Optimum band gap values, favourable band edge positions and stability in the electrolyte are critical parameters required for a semiconductor to have efficient photoelectrode properties. The present investigation carried out on the phase pure α & β MoO₃ thin film shows that the low bandgap β-MoO₃ possesses a mis-alignment with the water oxidation potential, while a more suitable band alignment is observed for the comparatively large bandgap α-MoO₃. Both experimental and DFT calculations show that the valence edge of the orthorhombic (α-MoO₃) phase is located at a higher energy (0.9 eV higher in VB-XPS and 1 eV higher in the DOS plots) than the monoclinic (β-MoO₃) phase, while the conduction edge value is roughly at the same energy level (?2.5 eV) in both polymorphs. Based on the above investigations, an all oxide heterojunction comprising of β-MoO₃/α-MoO₃ is found to be suitable for improved PEC performance due to favourable energy band diagram and increased visible light absorption in β-MoO₃. Significantly higher cathodic photocurrent is observed for the β-MoO₃/α-MoO₃ (1.6 mA/cm² at applied bias of ?0.3V_RHE under simulated 1 sun irradiation) as compared to the very low anodic response in β-MoO₃ (～1.0 nA/cm²) and α-MoO₃ (32 μA/cm²).