Vertical MoS on SiO/Si and graphene: effect of surface morphology on photoelectrochemical properties.

Two-dimensional materials have attracted intensive attention recently due to their unique optical and electronic properties and their promising applications in water splitting and solar cells. As a representative layer-structured of transition metal dichalcogenides, MoS has attracted considerable devotion owing to its exceptional photo and electro properties. Here, we show that the chemical vapour deposition (CVD) growth of MoS on Si photocathode and graphene/Si photocathode can be used to prepare photoelectrocatalysts for water splitting. We explore a bottom-up method to grow vertical heterostructures of MoS and graphene by using the two-step CVD. Graphene is first grown through ambient-pressure CVD on a Cu substrate and then transferred onto SiO/Si substrate by using the chemical wet transfer followed by the second CVD method to grow MoS over the graphene/SiO/Si. The effect of the growth temperatures of MoS is studied, and the optimum temperature is 800 °C. The MoS produced at 800 °C has the highest photocurrent density at -0.23 mA cm in 0.5 M NaSO and -0.51 mA cm in 0.5 M HSO at -0.8 V versus Ag/AgCl. The linear sweep voltammetry shows that MoS in 0.5 M HSO has about 55% higher photocurrent density than MoS in NaSO due to the higher concentration of protons (H) in the HSO electrolyte solution. Protons are reduced to H at lower overvoltage and hydrogen generation is thus enhanced at higher photocurrent density. MoS/graphene/SiO/Si (MGS) has -0.07 mA cm at -0.8 V versus Ag/AgCl of photocurrent density, which is 70% lower than that of bare MoS because MGS is thicker compared with MoS. Thus, MoS has potential as a photocatalyst in photoelectrochemical water splitting. The structure and the morphology of MoS play an important role in determining the photocurrent performance.