Vertical MoS₂ on SiO₂/Si and graphene: effect of surface morphology on photoelectrochemical properties

Abstract

Abstract 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 SiO 2 /Si substrate by using the chemical wet transfer followed by the second CVD method to grow MoS 2 over the graphene/SiO 2 /Si. The effect of the growth temperatures of MoS 2 is studied, and the optimum temperature is 800 °C. The MoS 2 produced at 800 °C has the highest photocurrent density at −0.23 mA cm −2 in 0.5 M Na 2 SO 4 and −0.51 mA 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. MoS 2 /graphene/SiO 2 /Si (MGS) has −0.07 mA 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 MoS 2 . 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.