Unconventionally Layered CoTe2 and NiTe2 as Electrocatalysts for Hydrogen Evolution

Abstract Two members of the transition metal ditelluride family, CoTe 2 and NiTe 2 , exist in multiple structures encompassing marcasite‐, pyrite‐ and CdI 2 related structures. The allotrope modification is influenced by weak changes in stoichiometry and synthesis. It is crucial to emphasize that the CdI 2 structure type is manifested by NiTe 2 while the CoTe 2 adopts a related structure for a non‐stoichiometric composition with ratio below 1:1.8. The obtained structure is based on LiTiS 2 which is derived from CdI 2 structure, however contains a polymeric cobalt network. Despite the atypical nature of their layered structure, layered phases of CoTe 1.8 and NiTe 2 are rarely cast into the spotlight. Here, layered CoTe 1.8 and NiTe 2 are investigated for their electrochemical and electrocatalytic properties. In electrocatalytic aspects, layered CoTe 1.8 and NiTe 2 demonstrate low overpotentials and small Tafel slopes that are quintessential features of hydrogen evolution electrocatalysts. These findings impart fundamental insights to the transition metal ditelluride family and affirm the prospective use of layered CoTe 1.8 and NiTe 2 in electrochemical applications.