Hydrogen Evolution at the In Situ MoO3/MoS2 Heterojunctions Created by Nonthermal O2 Plasma Treatment

Nonprecious two-dimensional materials, especially molybdenum sulfide (MoS2), have gained considerable attention due to their unique catalytic activity and stability for the hydrogen evolution reaction (HER). However, the constraint of MoS2 lies on the inactive basal planes, and the catalytic activity is limited to the active edge sites only. In this work, we are incorporating different defects into the multilayered MoS2 nanoflakes by the nonthermal oxygen (O-2) plasma technique to improve its catalytic activity. A mild O-2 plasma technique has been used to introduce different concentrations of dopants to improve the HER of 2D-MoS2 and to enhance the electron mobility of MoS2 nanosheets for fast electron transfer. Oxygen has been incorporated in MoS2 nanosheets which formed the nanocomposite material MoS2-xOx with sulfur-vacancies by controlled oxygen (O) plasma exposure. The best performance is obtained after irradiation of 30 s of O-2 plasma with an overpotential of 250 mV at 10 mA cm(-2). By employing density functional theory (DFT), it has also been shown that optimized insertion of oxygen in MoS2 can influence the electron density of states, leading to the faster charge transfer and consequent increase in catalytic activity. Our experimental (XRD, XPS, TEM) and theoretical (DFT) calculations show that O-doped 2D-MoS2 with S-edge termination exhibits superior activity and stability for the HER activity with low overpotential due to the fast electron transfer. The synergism between the optimal defect concentration along with the enhanced electron mobility increases the electrochemical activities in an acidic medium.