Understanding the Photocatalytic Activity of La₅Ti₂AgS₅O₇ and La₅Ti₂CuS₅O₇ for Green Hydrogen Production: Computational Insights

Green production of hydrogen is possible with photocatalytic water splitting, where hydrogen is produced while water is reduced by using energy derived from light. In this study, density functional theory (DFT) is employed to gain insights into the photocatalytic performance of La₅Ti₂AgS₅O₇ and La₅Ti₂CuS₅O₇-two emerging candidate materials for water splitting. The electronic structure of both bulk materials was calculated by using hybrid DFT, which indicated the band gaps and charge carrier effective masses are suitable for photocatalytic water splitting. Notably, the unique one-dimensional octahedral TiO _x S_6-x and tetragonal MS₄ channels formed provide a structural separation for photoexcited charge carriers which should inhibit charge recombination. Band alignments of surfaces that appear on the Wulff constructions of 12 nonpolar symmetric surface slabs were calculated by using hybrid DFT for each of the materials. All surfaces of La₅Ti₂AgS₅O₇ have band edge positions suitable for hydrogen evolution; however, the small overpotentials on the largest facets likely decrease the photocatalytic activity. In La₅Ti₂CuS₅O₇, 72% of the surface area can support oxygen evolution thermodynamically and kinetically. Based on their similar electronic structures, La₅Ti₂AgS₅O₇ and La₅Ti₂CuS₅O₇ could be effectively employed in Z-scheme photocatalytic water splitting.