Two-dimensional (2D) hybrid materials have been studied for use in photovoltaics, water splitting, sensors, batteries, and many other applications, which are prepared from popular 2D nanomaterials into heterojunctions or 3-dimensional (3D) frameworks. Benefiting from their unique 2D structures and tunable bandgaps, 2D hybrid materials can offer both a high surface area and a suitable work function. Molybdenum disulfide (MoS₂)/graphene hybrid material has been proved as a high-performance and low-cost catalyst for energy applications, but its optimum preparation condition is yet to be determined.

This work focuses on the 3D structure of MoS₂/graphene hybrid and primarily studies the crystallization condition and morphology change of MoS₂ in MoS₂/graphene hybrids by a temperature-varying hydrothermal method. Flower-like MoS₂ nanoflakes have been successfully grown on graphene nanosheets by using the hydrothermal method at temperatures from 150 to 240 ^oC. The resulting hybrid material was characterized to understand its temperature-dependent crystallization process and its electrochemical performance in the dye-sensitized solar cell and the hydrogen evolution reaction. Through high-resolution scanning electron microscopy and high-resolution transmission electron microscopy, the 3D structures can be clearly observed and compared. X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy are taken to identify the crystallization differences among different samples and understand temperature effects. The highest electrocatalytic efficiency for both the DSSC and the HER was obtained by preparing the MoS₂/graphene hybrid at 180 ^oC, which benefits from both high reactivity of MoS₂ 1T phase and high conductivity of the hybrid structure. This research leads to a better understanding of temperature dependence of MoS₂ crystallization and gives directions for better catalytic material design.