Ultrathin transition metal oxychalcogenides

Abstract Two-dimensional (2D) transition metal dichalcogenides (TMDs) exfoliated from bulk layered materials possess interesting properties. Most transition metal oxides (TMOs) are not layered and therefore cannot be exfoliated. Here we report the synthesis of a new family of ultrathin materials – transition metal oxychalcogenides (TMOCs) and demonstrate their unique properties. Specifically, 2D TMOCs such as HfSxOy, ZrSxOy, TiSxOy, TaSxOy, NbSxOy, VSexOy, HfSexOy, ZrSexOy, TaTexOy (x, y ~ 0–2) from bulk TMDs (HfS₂, ZrS₂, TiS₂, TaS₂, NbS₂, VSe₂, HfSe₂, ZrSe₂, TaTe₂) have been fabricated using tetrabutylammonium intercalation. The stoichiometry of TMOCs can be adjusted, which enables control of their optical band gaps and tunability of electrical conductivity by more than 8 orders of magnitude. Our results show that by tuning the chalcogen to oxygen ratio along with local atomic structure in TMOCs, it is possible to impart unexpected properties. For example, in contrast to conventional TMDs, the hybrid structure renders TMOCs surprisingly stable and electrochemically active in strong acids, which allows them to be used as proof-of-concept catalysts for the oxygen evolution reaction (OER) at pH ≈ 0. The HfS0.52O1.09 catalysts show high mass activity (10,3000 A g–¹ at an overpotential of 0.5 V) and exhibit durability in proton exchange membrane (PEM) water electrolysers.