Controlling the dendritic structure and the photo-electrocatalytic properties of highly crystalline MoS2 on sapphire substrate. (25th June 2018) - Ma, Jun
Abstract: 2D crystalline MoS2 flakes with the dendritic shape have been controllably fabricated on a sapphire (0 0 0 1) substrate for catalytic applications in the hydrogen evolution reaction (HER) using atmospheric pressure chemical vapor deposition (CVD). The proposed growth process was controlled by separately setting the temperature of two precursors and heating MoO3 for 15 min in advance compared with the sulfur source. Then, under a sulfur-rich condition, the desired dendritic MoS2 monolayer flakes were obtained and exhibited a threefold symmetric feature. The individual branch of MoS2 dendrites was distinguished to be consisted of tiny triangular structures sequentially arranged by the corner to the bottom along the specific crystalline orientations. The shape evolution from the dendritic to the compact triangular morphology was further observed strongly depending on their regions located on the substrate along the carrier gas flow. The mechanism underlying the entire evolution process was discussed in relation to the CVD growth parameters, such as the sulfur-to-metal (S/M) flux ration, the introduction time of sulfur and the substrate symmetry. By carefully tailoring the growth condition, the large scale MoS2 dendrites monolayer flakes were obtained on sapphire substrate, which was strictly transferred on the Au foil to detect the photo-electrocatalytic properties. The photo-electrocatalytic HER of the thus dendritic MoS2 crystalline flakes and the compact triangular structures with different domain edge lengths in the same unit area were analytically compared. The lowered Tafel slope and the large exchange current density of the high-porous edge-exposed MoS2 dendrites in HER demonstrated that they are a promising HER catalyst.