Vertical MoS2on SiO2/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(2)has attracted considerable devotion owing to its exceptional photo and electro properties. Here, we show that the chemical vapour deposition (CVD) growth of MoS(2)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(2)and graphene by using the two-step CVD. Graphene is first grown through ambient-pressure CVD on a Cu substrate and then transferred onto SiO2/Si substrate by using the chemical wet transfer followed by the second CVD method to grow MoS(2)over the graphene/SiO2/Si. The effect of the growth temperatures of MoS(2)is studied, and the optimum temperature is 800 degrees C. The MoS(2)produced at 800 degrees C has the highest photocurrent density at -0.23 mA degrees cm(-2)in 0.5 M Na(2)SO(4)and -0.51 mA degrees cm(-2)in 0.5 M H(2)SO(4)at -0.8 V versus Ag/AgCl. The linear sweep voltammetry shows that MoS(2)in 0.5 M H(2)SO(4)has about 55% higher photocurrent density than MoS(2)in Na(2)SO(4)due to the higher concentration of protons (H+) in the H(2)SO(4)electrolyte solution. Protons are reduced to H(2)at lower overvoltage and hydrogen generation is thus enhanced at higher photocurrent density. MoS2/graphene/SiO2/Si (MGS) has -0.07 mA degrees cm(-2)at -0.8 V versus Ag/AgCl of photocurrent density, which is 70% lower than that of bare MoS(2)because MGS is thicker compared with MoS2. Thus, MoS(2)has potential as a photocatalyst in photoelectrochemical water splitting. The structure and the morphology of MoS(2)play an important role in determining the photocurrent performance.

Automated summary

Two-dimensional materials like MoS(2) are promising for applications in water splitting due to their unique properties. The growth of MoS(2) and graphene vertical heterostructures using CVD techniques shows potential for photoelectrocatalyst preparation. Optimal growth temperature for MoS(2) is found to be 800 degrees Celsius.