Simultaneous Electrochemical Exfoliation and Functionalization of 2H-MoS2

MoS2 is a promising semiconducting material that has been widely studied for applications in catalysis and energy storage. The covalent chemical functionalization of MoS2 can be used to tune the optoelectronic and chemical properties of MoS2 for different applications. However, 2H-MoS2 is typically chemically inert and difficult to functionalize directly and thus requires pre-treatments such as a phase transition to 1T-MoS2 or argon plasma bombardment to introduce reactive defects. Apart from being inefficient and inconvenient, these methods can cause a degradation of the desirable properties and introduce unwanted defects. Here, we report a facile and scalable procedure of fabricating functionalized thin (~4 nm) MoS2 layers. We demonstrate that 2H-MoS2 can be simultaneously electrochemically exfoliated and functionalized. The aryl diazonium salts used for functionalization have not only been successfully grafted onto the 2H-MoS2, as verified by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, but also aid the exfoliation. Electrochemical characterization of MoS2 supercapacitors revealed that the specific capacitance of electrodes produced using this material was increased by 25% when functionalized. This electrochemical functionalization technique could possibly be extended to other types of transition metal dichalcogenides (TMDs), which are also chemically inert, with different functional species to adjust to specific applications.