Contacting MoS2 to MXene: Vanishing p-Type Schottky Barrier and Enhanced Hydrogen Evolution Catalysis

It is a big challenge to make a Schottky-barrier (SB)-free hole contact to MoS2 with a high ionization of similar to 6.0 eV. Here, using first-principles calculations, in a recently discovered large family of two-dimensional transition metal carbides or nitrides (MXenes), we have found six materials (V2CO2, Cr2CO2, Mo2CO2, V4C3O2, Cr2NO2, and V2NO2) that can be used as metal contacts to monolayer MoS2 with vanishing p-type Schottky barriers at contacting interfaces, resulting in highly efficient hole injection into MoS2. We reveal that the successful achievements of the SB-free hole contacts at these MoS2/MXene interfaces depend on not only the high work functions of the MXenes but also the absence of the formation of interfacial gap states that usually result in strong Fermi level pinning in the midgap of a semiconductor. We further propose that efficient charge injection into MoS2 facilitated by SB-free contact could also increase the hydrogen evolution reaction (HER) activity of the 2H-MoS2 basal plane by improving its conductivity as well as its ability to adsorb hydrogen. Not only are these findings invaluable for designing high-performance MoS2-based electronic devices but they provide an effective route to optimize MoS2 nanosheet catalysts for the HER.