Double-Hole-Mediated Codoping on KNbO3 for Visible Light Photocatalysis

Insight into the Effect of Anionic–Anionic Co-Doping on BaTiO3 for Visible Light Photocatalytic Water Splitting: A First-Principles Hybrid Computational Study

In this research, we thoroughly studied the electronic properties and optical absorption characteristics with double-hole coupling of anions–anion combinations for designing effective photocatalysts for water redox using first-principles methods within the hybrid Heyd–Scuseria–Ernzerhof (HSE06) exchange–correlation formalisms. The findings reveal that the values of formation energy of both the anion mono- and co-doped configurations increase monotonically as the chemical potential of oxygen decreases. The N–N co-doped BaTiO3 exhibits a more favorable formation energy under an O-poor condition compared with other configurations, indicating that N and N pairs are more likely to be synthesized successfully. Interestingly, all the co-doping configurations give a band gap reduction with suitable position for oxygen production and hydrogen evolution. The obtained results demonstrate that all the co-doped systems constitute a promising candidate for photocatalytic water-splitting reactions. Furthermore, the enhanced ability of the anionic-anionic co-doped BaTiO3 to absorb visible light and the positions of band edges that closely match the oxidation-reduction potentials of water suggest that these configurations are viable photocatalysts for visible-light water splitting. Therefore, the wide-band gap semiconductor band structures can be tuned by double-hole doping through anionic combinations, and high-efficiency catalysts for water splitting using solar energy can be created as a result.

Rotational design of BP/XY2 (X = Mo, W; Y = S, Se) composites for overall photocatalytic water-splitting

Photocatalytic water-splitting for hydrogen generation is a promising way to solve the energy crisis, yet the design of efficient photocatalysts is still a challenge. By utilization of first principles calculations, we predict the photocatalytic properties of monolayer boron phosphide (BP) based BP/XY₂ (X  =  Mo, W; Y  =  S, Se) composites of different rotated configurations. Our results suggest that the BP/XY₂ composites can be stably formed, and the narrowed bandgaps ensure these composites are suitable for absorbing visible light. The bandgaps and band edge positions are slightly affected by the rotation angles. The BP/MoS₂, BP/MoSe₂, and BP/WSe₂ are type II heterostructures. Furthermore, the transferred charge from BP to XY₂ layers leads to the formation of electric fields, which efficiently separate the photoinduced carriers. The band alignments of BP/MoS₂, BP/MoS₂, BP/MoSe₂, and BP/WSe₂ satisfy the requirements of overall water-splitting within the pH scope of 3.6-7.9, 6.8-7.9, 4.0-8.0, and 8.7-8.8. This work will provide valuable insight for designing efficient water-splitting photocatalysts.

Two dimensional ZnO/AlN composites used for photocatalytic water-splitting: a hybrid density functional study

Using hybrid density functionals, we study the interfacial interactions and electronic properties of ZnO/AlN composites with the consideration of rotation angles and biaxial strains in order to enhance the photocatalytic performance for water-splitting. The different rotated composites, and -2% strained, original, and 2% strained ZnO/AlN composites can be easily prepared owing to the negative interface formation energies. The bandgaps and band alignments of ZnO/AlN composites can be significantly tuned by biaxial strains. Particularly, the appropriate bandgap for visible light absorption, proper band alignment for spontaneous water-splitting, and the formed electric field promoting photoinduced carrier separation make the 2% strained ZnO/AlN composite a potential candidate for photocatalytic water-splitting. This work shines some light on designing two dimensional heterostructured photocatalysts.

Strain-Tunable Visible-Light-Responsive Photocatalytic Properties of Two-Dimensional CdS/g-C₃N₄: A Hybrid Density Functional Study

By means of a hybrid density functional, we comprehensively investigate the energetic, electronic, optical properties, and band edge alignments of two-dimensional (2D) CdS/g-C 3 N 4 heterostructures by considering the effect of biaxial strain and pH value, so as to improve the photocatalytic activity. The results reveal that a CdS monolayer weakly contacts with g-C 3 N 4 , forming a type II van der Waals (vdW) heterostructure. The narrow bandgap makes CdS/g-C 3 N 4 suitable for absorbing visible light and the induced built-in electric field between the interface promotes the effective separation of photogenerated carriers. Through applying the biaxial strain, the interface adhesion energy, bandgap, and band edge positions, in contrast with water, redox levels of CdS/g-C 3 N 4 can be obviously adjusted. Especially, the pH of electrolyte also significantly influences the photocatalytic performance of CdS/g-C 3 N 4 . When pH is smaller than 6.5, the band edge alignments of CdS/g-C 3 N 4 are thermodynamically beneficial for oxygen and hydrogen generation. Our findings offer a theoretical basis to develop g-C 3 N 4 -based water-splitting photocatalysts.

Material Design for Photocatalytic Water Splitting from a Theoretical Perspective

Currently, problems associated with energy and environment have become increasingly serious. Producing hydrogen, a clean and renewable resource, through photocatalytic water splitting using solar energy is a feasible and efficient route for resolving these problems, and great efforts have been devoted to improve the solar-to-hydrogen efficiency. Light harvesting and electron-hole separation are key in enhancing the efficiency of solar energy utilization, which stimulates the development of new photocatalytic materials. Here, recent advances in material design for photocatalytic water splitting are presented from a theoretical perspective. Specifically, aiming to enhance the photocatalytic performance, general strategies of materials design are discussed, including codoping and introducing a built-in electric field to improve the light harvesting of materials, reducing the dimension of materials to shorten the migration pathway of carriers to inhibit electron-hole recombination, and constructing heterojunctions to enhance light harvesting and electron-hole separation. Future opportunities and challenges in the theoretical design of photocatalytic materials toward water splitting are also included.

ZnO/MoX2 (X = S, Se) composites used for visible light photocatalysis

Hybrid density functional has been adopted to investigate the structural, electronic, and optical properties of ZnO/MoS₂ and ZnO/MoSe₂ composites as compared with the results of ZnO, MoS₂, and MoSe₂ monolayers. The results indicate that MoS₂ and MoSe₂ monolayers could contact with monolayer ZnO to form ZnO/MoS₂ and ZnO/MoSe₂ heterostructures through van der Waals (vdW) interactions. The calculated bandgap of ZnO/MoS₂ (ZnO/MoSe₂) is narrower than that of ZnO or MoS₂ (MoSe₂) monolayers, facilitating the shift of light absorption edges of the composites towards visible light in comparison with bare ZnO and MoX₂ monolayers. Through the application of strain, the ZnO/MoS₂ and ZnO/MoSe₂ composites which own suitable bandgaps, band edge positions, efficient charge separation, and good visible light absorption will be promising for visible light photocatalytic water splitting. These results provide a route for design and development of efficient ZnO/MoS₂ and ZnO/MoSe₂ photocatalysts for water splitting.

The ZnO/MoS₂ (ZnO/MoSe₂) heterostructures with the strain of –2% (+2%) have suitable bandgap and band edge position for hydrogen production via visible light photocatalytic water splitting.