  Alloying in 2D materials plays a more and more important role due to wide
range bandgap tunability and integrating the advantages of HER and OER. Here,
the novel bilayers of SnO/BiOX (X= Cl, Br and I) bilayer are constructed to
integrate the advantages of narrow bandgap and separating photo-generated
carriers. The bandgap of the bilayers can be tuned from 1.09 to 1.84 eV,
remarkably improving the utilization of solar energy. The large difference in
effective masses and built-in electric field effectively hamper the fast
recombination of photo-generated carries, which highly enhances the
photocatalytic efficiency. Besides that, the type-II band alignment guarantee
the two half reactions could occur at different surfaces. Moreover, the optical
absorption (the strong transition between band edges and high joint density of
states) and band-edge level further confirm the SnO/BiOX (X= Cl and Br) bilayer
is a promising candidate for overall water-splitting.
