Unconventionally Layered CoTe2 and NiTe2 as Electrocatalysts for Hydrogen Evolution.

Two members of the transition metal ditelluride family, CoTe2 and NiTe2 , exist in multiple structures encompassing marcasite-, pyrite- and CdI2 related structures. The allotrope modification is influenced by weak changes in stoichiometry and synthesis. It is crucial to emphasize that the CdI2 structure type is manifested by NiTe2 while the CoTe2 adopts a related structure for a non-stoichiometric composition with ratio below 1:1.8. The obtained structure is based on LiTiS2 which is derived from CdI2 structure, however contains a polymeric cobalt network. Despite the atypical nature of their layered structure, layered phases of CoTe1.8 and NiTe2 are rarely cast into the spotlight. Here, layered CoTe1.8 and NiTe2 are investigated for their electrochemical and electrocatalytic properties. In electrocatalytic aspects, layered CoTe1.8 and NiTe2 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 CoTe1.8 and NiTe2 in electrochemical applications.