Comparative study on MoS2 and WS2 for electrocatalytic water splitting

Replacing Pt by earth abundant catalysts is one of the most important tasks toward potential large-scale HER applications. Among many potential candidates, low cost and earth abundant transition metal dichalcogenides such as MoS₂ and WS₂ have been promising as good H₂ evolution electrocatalysts when they are engineered into the structures with active sites. In this work, we have performed systematic studies on the catalytic reactivity of both MoS₂ and WS₂ materials produced by one-step and scalable thermolysis from (NH₄)₂WS₄ and (NH₄)₂MoS₄ precursors respectively. Structural analysis shows that these materials prepared at a higher thermolysis temperature exhibit higher crystallinity. The H₂ evolution electrocatalysts efficiency for the MoS₂ prepared at a lower temperature is higher than those at higher temperatures, where amorphous MoS₂ or S₂²⁻${{\text{S}}_2}^{2-}$ species instead of crystalline MoS₂ is the main active site. By contrast, crystalline WS₂ prepared at high temperature is identified to be the key reaction site. Both catalysts display excellent efficiency and durability as an electrocatalyst operating in acidic electrolytes. This work provides fundamental insights for further design and preparation of emergent metal dichalcogenide catalysts, beneficial for the development in clean energy.