Atomically thin 2D materials with high surface areas allow engineering its physical and chemical properties with help of combining or decorating with different classes of materials. The hybrid or heterostructure of two different atomically thin materials exhibits completely different chemical and electronics behavior as compared to its parent components. Here, MoS2 quantum dots (QDs) are decorated onto ultrathin NiO nanosheets (NSs) by using a one-pot hydrothermal process. Uniformly dispersed MoS2 QDs and ultrathin NiO NSs hybrid/heterostructure can provide more active reaction sites and accelerate the charge transfer rate. Benefiting from the heterointerfaces synergistic effect between MoS2 QDs and NiO NSs, the MoS2 QDs/NiO NSs electrode exhibits excellent electrocatalytic activity towards both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a bifunctional electrocatalyst, the MoS2 QDs/NiO NSs electrode has achieved highly efficient overall water splitting activity, which needs a low voltage of 1.61 V to deliver a 10 mA cm(-2) with superior stability. (C) 2020 Elsevier Inc. All rights reserved.