2D WSe2/MoSi2N4 type-II heterojunction with improved carrier separation and recombination for photocatalytic water splitting

[Display omitted] •Type-II WSe2/MoSi2N4 heterojunction promotes the separation of photoexcited electron-hole pairs.•The rapid separation and slow recombination of the photoexcited electron-hole pairs demonstrate the high quantum efficiency of WSe2/MoSi2N4 heterojunction.•WSe2/MoSi2N4 heterojunction possesses superior optical absorption (105 cm−1), low overpotential for OER (0.60 V), and outstanding light absorption properties.•The photocatalytic water splitting can occur spontaneously on the surface of WSe2/MoSi2N4 heterojunction. The use of semiconductor photocatalysis for hydrogen production is an ideal approach for achieving solar energy and conversion. In this work, we systematically examine the photocatalytic properties of WSe2/MoSi2N4 van der Waals heterojunctions using first-principles calculation and nonadiabatic molecular dynamics. The results demonstrate that the WSe2/MoSi2N4 heterojunction possesses a 1.81 eV indirect band gap and type-II band alignment, which ensures that the photoexcited electron–hole (e–h) pairs are spatially separated. The carrier lifetime of the photoexcited e–h pairs is 278 ps significantly longer than the interlayer hole transfer time of 335 fs, implying that the heterojunction has the high quantum efficiency. In addition, this heterojunction possesses superior optical absorption (105 cm−1), low overpotential for OER (0.60 V), and outstanding light absorption properties. These findings indicate that this heterojunction can achieve highly efficient and spontaneous photocatalytic water splitting.