Enhanced hydrogen evolution reaction in surface functionalized mos₂ monolayers

Monolayered, semiconducting MoS₂ and their transition metal dichalcogenides (TMDCs) families are promising and low-cost materials for hydrogen generation through electrolytes (HER, hydrogen evolution reaction) due to their high activities and electrochemical stability during the reaction. However, there is still a lack of understanding in identifying the underlying mechanism responsible for improving the electrocatalytic properties of theses monolayers. In this work, we investigated the significance of controlling carrier densities in a MoS₂ monolayer and in turn the corresponding electrocatalytic behaviors in relation to the energy band structure of MoS₂ . Surface functionalization was employed to achieve p-doping and n-doping in the MoS₂ monolayer that led to MoS₂ electrochemical devices with different catalytic performances. Specifically, the electron-rich MoS₂ surface showed lower overpotential and Tafel slope compared to the MoS₂ with surface functional groups that contributed to p-doping. We attributed such enhancement to the increase in the carrier density and the corresponding Fermi level that accelerated HER and charge transfer kinetics. These findings are of high importance in designing electrocatalysts based on two-dimensional TMDCs.