Abstract The development of novel efficient and robust electrocatalysts with sufficient active sites is one of the key parameters for hydrogen evolution reactions (HER) catalysis, which plays a key role in hydrogen production for clean energy harvesting. Recently, two-dimensional (2D) materials, especially molybdenum disulfide (MoS2), have gained attention for the catalysis of hydrogen production catalysis because of their exceptional properties. Innovative strategies are have been developed to engineer these material systems for improvements in their catalytic activity. Toward this aim, we report the in situ growth of MoS2 structure by sulfurization of reduced graphene oxide (rGO) supported molybdenum oxide (MoO2) particles using the chemical vapor deposition (CVD ) method. This approach created various morphologies of MoS2 with large edges and defect densityies on the basal plane of rGO supported MoS2 structures, which are considered as active sites for HER catalysis. In addition, MoS2 nanostructures on the surface of the porous rGO network show robust physical interactions, such as van der Waals and π-π interactions between MoS2 and rGO, as well as free of aggregation. These features result in an improved HER catalysis. In order to gain a better understanding of the improvement of HER catalyst of MoS2, fully atomistic molecular dynamics (MD) simulations of different defect geometries were also performed.