By varying the organic substituents on two-dimensional transition metal dichalcogenides (2D TMDCs), we can alter the fundamental electric properties of 2D TMDCs, such as molybdenum disulfide (MoS2). We show that the 2D-MoS2 surface energetics and stability can be controlled by chemical modification of the surface via organic molecules with varying electronics. Chemically-exfoliated, metallic MoS2 is modified with substituted aryl rings containing substituents with various electron withdrawing/donating groups (p-NO2, 3,5-Cl2, p-Br, p-OCH3, and p-Et2N). This functionalization results in different electrochemical properties, specifically activity towards the hydrogen evolution reaction (HER). As the Hammett parameter is changed, different exchange currents as well as Tafel slopes are observed for the modified surfaces. In addition, the workfunction of the metallic MoS2 surface depends on the functional group, and there is a correlation between the electron withdrawing/donating character (Hammett parameter) of the functional group and the workfunction, which is measured via X-ray photoelectron spectroscopy. Furthermore, the metallic nature of the MoS2 films are preserved by the functional group and do not undergo conversion to the semiconducting state when annealed at 150 °C for 24 h. This result is critical to maintaining the catalytically active metallic state of 2D MoS2, which is verified via extended electrochemistry experiments. Functionalizing 2D TMDCs gives an extra handle on electronic properties and stability within the typically unstable metallic state.

Controlling the energetics and stability of metallic 2D MoS2 with surface modifiers

254th National Meeting (2017)

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