First-Principles Investigation on the Tunable Electronic Structures and Photocatalytic Properties of AlN/Sc₂CF₂ and GaN/Sc₂CF₂ Heterostructures

Heterostructure catalysts are highly anticipated in the field of photocatalytic water splitting. AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures are proposed in this work, and the electronic structures were revealed with the first-principles method to explore their photocatalytic properties for water splitting. The results found that the thermodynamically stable AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures are indirect semiconductors with reduced band gaps of 1.75 eV and 1.84 eV, respectively. These two heterostructures have been confirmed to have type-Ⅰ band alignments, with both VBM and CBM contributed to by the Sc₂CF₂ layer. AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures exhibit the potential for photocatalytic water splitting as their VBM and CBM stride over the redox potential of water. Gibbs free energy changes in HER occurring on AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures are as low as −0.31 eV and −0.59 eV, respectively. The Gibbs free energy change in HER on the AlN (GaN) layer is much lower than that on the Sc₂CF₂ surface, owing to the stronger adsorption of H on AlN (GaN). The AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures possess significant improvements in absorption range and intensity compared to monolayered AlN, GaN, and Sc₂CF₂. In addition, the band gaps, edge positions, and absorption properties of AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures can be effectively tuned with strains. All the results indicate that AlN/Sc₂CF₂ and GaN/Sc₂CF₂ heterostructures are suitable catalysts for photocatalytic water splitting.