2D Thin Sheet Heterostructures of MoS₂ on MoSe₂ as Efficient Electrocatalyst for Hydrogen Evolution Reaction in Wide...

Two-dimensional layered transition metal dichalcogenides, MoSe₂ and MoS₂, have drawn potential attention in the field of water splitting. Coupling of MoS₂ and MoSe₂ provides a sustainable route to improve the electrocatalytic activity for the hydrogen evolution reaction (HER). Here, the heterostructures of thin sheets (ts) of MoSe₂ and MoS₂ are combined to develop the MoSe₂-ts@MoS₂-ts heterostructure via multiple-step methodology. First, thin sheets of MoSe₂ are synthesized following the stepwise hydrothermal method. After the successful synthesis of MoSe₂-ts, MoS₂-ts is synthesized on it to develop the heterostructure: MoSe₂-ts@MoS₂-ts. By tuning the amount of MoS₂-ts and MoSe₂-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 H₂SO₄. MoSe₂-ts@MoS₂-ts can generate 10 mA/cm² 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 H₂. 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. MoSe₂-ts@MoS₂-ts has very high stability during the electrocatalytic reaction, which is determined from 1000 consecutive cycles and a 24 h prolonged scan. MoSe₂-ts@MoS₂-ts can generate 147 μmol of H₂ in ∼50 min of reaction time with 100% Faradaic efficiency.