Enhancing the catalytic activity of the alkaline hydrogen evolution reaction by tuning the S/Se ratio in the Mo(SSe) catalyst

The alkaline hydrogen evolution reaction (HER) plays a key role in photo(electro)catalytic water splitting technologies, particularly in water-alkali electrolyzers. Unfortunately, although transition metal dichalcogenide (TMD) materials, especially MoS 2 and MoSe 2 , are considered efficient, Earth-abundant catalysts for the HER in an acidic electrolyte, they are much less effective under high pH conditions due to a sluggish water dissociation process (Volmer-step) and strong adsorption of the OH − intermediate on their surfaces. Herein we show a novel synergetic effect obtained by tailoring the S/Se ratio in Mo(S x Se 1− x ) 2 alloys. We were able to influence the metal oxidation state and d-band to optimize the catalytic sites for H OH dissociation and OH − desorption while maintaining favourable M-H energetics. The Mo(S x Se 1− x ) 2 ( x = 0.58) catalyst exhibited high performance with an onset potential of −43 mV in 0.5 M KOH, i.e. , ∼3 and ∼4-fold less than that for MoSe 2 and MoS 2 , respectively. The results obtained in the current study have implications for the rational design of cost-effective electro-catalysts for water reduction based on TMD alloys. Stronger together : Alloying allows the optimization of the binding properties of Mo(S x Se 1− x ) 2 nanoflowers such that their catalytic activity towards hydrogen production is enhanced in alkaline solution.