Improved hydrogen evolution activity by unique NiS2-MoS2 heterostructures with misfit lattices supported on poly(ionic liquid)s functionalized polypyrrole/graphene oxide nanosheets

Abstract

Unique NiS2-MoS2 heterostructures with misfit lattices composed of cubic NiS2, metallic 1 T-MoS2 and semiconductive 2H-MoS2 have been immobilized on poly(1-vinyl-3-ethylimidazolium bromide) functionalized polypyrrole/graphene oxide via an ordinary hydrothermal procedure. The obtained NiS2-MoS2/PVEIB/PPy/GO nanosheets exhibited the excellent electrocatalytic performance for hydrogen evolution reaction (HER). PVEIB played an essential role in the fabrication of this inorganic/organic hierarchical lamellar micro-/nanostructures, which not only played as a good connector between transition metal dichalcogenides (TMDCs) heterostructures and PPy/GO, inducing the formation of metallic 1 T-MoS2, but also effectively stabilized more electrons and further facilitate the Heyrovsky reaction for the generation and release of H2. Though NiS2 possessed poor conductivity and induced partial 1 T-MoS2 transformed to 2H-MoS2 on PVEIB/PPy/GO, the preeminent HER activity was still gained, because NiS2 could effectively prevent the oxidation of MoS2 exposed in the atmosphere. Especially, the crystal phase transition of MoS2 from 1 T to 1 T’ phase in NiS2-MoS2/PVEIB/PPy/GO could be detected by XPS after long-term HER test. Therefore, poly(ionic liquid)s and another metal ion would induce the crystal structures of TMDCs and optimize their electrocatalytic performance, which might afford a new thought towards the reasonable design of electrocatalysts based on TMDCs for electrochemical water splitting.