The Origin of High Activity of Amorphous MoS2 in the Hydrogen Evolution Reaction

Abstract

Molybdenumdisulfide(MoS2)and related transition metal chal-cogenides can replace expensive preciousmetal catalysts suchas Pt for the hydrogen evolution reaction(HER). The relationsbetween the nanoscale properties and HER activity of well-controlled 2H and Li-promoted1Tphases of MoS2,aswell asan amorphous MoS2phase, have been investigated and ade-tailed comparison is made on Mo@Sand Mo@Mo bond analysisunder operando HER conditions, which reveals asimilar bondstructure in 1T and amorphous MoS2phases as akey feature inexplaining their increased HER activity.Whereasthe distinctbond structure in 1T phase MoS2is caused by Li+intercalationand disappears under harsh HER conditions, amorphous MoS2maintainsits intrinsic short Mo@Mo bond feature and, withthat, its high HER activity.Quantum-chemical calculations indi-cate similarelectronic structures of small MoS2clusters servingas modelsfor amorphous MoS2and the 1T phase MoS2,show-ing similarGibbs free energies for hydrogen adsorption (DGH*)and metalliccharacter.