First-principles analysis of AlSb/ZnTe van der Waals heterostructure as a self-driven photocatalyst for complete water splitting

Combining two monolayers with complementary, redox-active band edges in a single van der Waals heterostructure is an effective way to lift the single-half-reaction limitation that constrains most twodimensional photocatalysts. Here, density functional theory calculations are used to characterize the structural, electronic, optical, and photocatalytic behaviour of a novel two-dimensional AlSb/ZnTe heterostructure. The stacked configuration is energetically favourable, with a binding energy of −26.2 meV/Å2 and a lattice mismatch of just 0.69%, and its dynamical and thermal stability are confirmed by phonon dispersion calculations and 300 K ab initio molecular dynamics. The heterostructure develops a type-II, staggered band alignment with an indirect energy band-gap of 1.55 eV, spatially separating photogenerated electrons and holes into the AlSb and ZnTe layers, respectively, across the entire pH range. The resulting band edges bracket both water redox potentials, satisfying the thermodynamic requirement for overall water splitting. Holes are found to be more mobile than electrons (effective masses of 0.67 𝑚0 and 0.84 𝑚0, respectively), which is advantageous given that oxygen evolution is the kinetically limiting half-reaction. With a carrier utilization efficiency of 56.97%, a corrected solar-to-hydrogen efficiency of 23.42% is obtained, positioning the AlSb/ZnTe heterostructure as a self-driven candidate for solar-powered hydrogen production.