The origin of high activity of amorphous MoS2 in the hydrogen evolution reaction

Abstract

\u3cp\u3eMolybdenum disulfide (MoS \u3csub\u3e2\u3c/sub\u3e) and related transition metal chalcogenides can replace expensive precious metal catalysts such as Pt for the hydrogen evolution reaction (HER). The relations between the nanoscale properties and HER activity of well-controlled 2H and Li-promoted 1T phases of MoS \u3csub\u3e2\u3c/sub\u3e, as well as an amorphous MoS \u3csub\u3e2\u3c/sub\u3e phase, have been investigated and a detailed comparison is made on Mo−S and Mo−Mo bond analysis under operando HER conditions, which reveals a similar bond structure in 1T and amorphous MoS \u3csub\u3e2\u3c/sub\u3e phases as a key feature in explaining their increased HER activity. Whereas the distinct bond structure in 1T phase MoS \u3csub\u3e2\u3c/sub\u3e is caused by Li \u3csup\u3e+\u3c/sup\u3e intercalation and disappears under harsh HER conditions, amorphous MoS \u3csub\u3e2\u3c/sub\u3e maintains its intrinsic short Mo−Mo bond feature and, with that, its high HER activity. Quantum-chemical calculations indicate similar electronic structures of small MoS \u3csub\u3e2\u3c/sub\u3e clusters serving as models for amorphous MoS \u3csub\u3e2\u3c/sub\u3e and the 1T phase MoS \u3csub\u3e2\u3c/sub\u3e, showing similar Gibbs free energies for hydrogen adsorption (ΔG \u3csub\u3eH*\u3c/sub\u3e) and metallic character. \u3c/p\u3