2D Thin Sheet Heterostructures of MoS on MoSe as Efficient Electrocatalyst for Hydrogen Evolution Reaction in Wide pH Range.

Two-dimensional layered transition metal dichalcogenides, MoSe and MoS, have drawn potential attention in the field of water splitting. Coupling of MoS and MoSe provides a sustainable route to improve the electrocatalytic activity for the hydrogen evolution reaction (HER). Here, the heterostructures of thin sheets (ts) of MoSe and MoS are combined to develop the MoSe-ts@MoS-ts heterostructure via multiple-step methodology. First, thin sheets of MoSe are synthesized following the stepwise hydrothermal method. After the successful synthesis of MoSe-ts, MoS-ts is synthesized on it to develop the heterostructure: MoSe-ts@MoS-ts. By tuning the amount of MoS-ts and MoSe-ts in the heterostructure separately, the optimum condition is obtained for HER. The unique heterostructure is efficient for HER under wide pH conditions like 1 M KOH, pH-7 phosphate buffer, 3.5% saline water, and finally 0.5 M HSO. MoSe-ts@MoS-ts can generate 10 mA/cm current density under the application of -0.186 V vs RHE with a low Tafel value of 71 mV/decade. The formation of the heterojunction plays an essential role in facilitating charge transportation. Furthermore, the heterostructure provides the more active sites for the adsorption of hydrogen to generate H. An excess amount of any of the bare counter parts in the heterostructure leads to a decrease in electrocatalytic efficiency because of the lowered heterojuction formation. MoSe-ts@MoS-ts has very high stability during the electrocatalytic reaction, which is determined from 1000 consecutive cycles and a 24 h prolonged scan. MoSe-ts@MoS-ts can generate 147 μmol of H in ∼50 min of reaction time with 100% Faradaic efficiency.