Edge reconstruction of layer-dependent β-In2Se3/MoS2 vertical heterostructures for accelerated hydrogen evolution

The layer-dependent properties are still unclarified in two-dimensional (2D) vertical heterostructures. In this study, we layer-by-layer deposited semimetal beta-In2Se3 on monolayer MoS2 to form vertical beta-In2Se3/MoS2 heterostructures by chemical vapor deposition. The defect-mediated nucleation mechanism induces beta-In2Se3 nanosheets to grow on monolayer MoS2, and the layer number of stacked beta-In2Se3 can be precisely regulated from 1 layer (L) to 13 L by prolonging the growth time. The beta-In2Se3/MoS2 heterostructures reveal tunable type-II band alignment arrangement by altering the layer number of beta-In2Se3, which optimizes the internal electron transfer. Meanwhile, the edge atomic structure of beta-In2Se3 stacking on monolayer MoS2 shows the reconstruction derived from large lattice mismatch (similar to 29%), and the presence of beta-In2Se3 also further increases the electrical conductivity of beta-In2Se3/MoS2 heterostructures. Attributed to abundant layer-dependent edge active sites, edge reconstruction, improved hydrophilicity, and high electrical conductivity of beta-In2Se3/MoS2 heterostructures, the edge of beta-In2Se3/MoS2 heterostructures exhibits excellent electrocatalytic hydrogen evolution performance. Lower onset potential and smaller Tafel slope can be observed at the edge of monolayer MoS2 coupled with 13-L beta-In2Se3. Hence, the outstanding conductive layers coupled with edge reconstruction in 2D vertical heterostructures play decisive roles in the optimization of electron energy levels and improvement of layer-dependent catalytic performance.