New Simultaneous Exfoliation and Doping Process for Generating MX2 Nanosheets for Electrocatalytic Hydrogen Evolution Reaction.

Abstract

Doping nonmetal atoms into layered transition metal dichalcogenide MX2 structures has emerged as a promising strategy for enhancing their catalytic activities for the hydrogen evolution reaction. In this study, we developed a new and efficient one-step approach that involves simultaneous plasma-induced doping and exfoliating of MX2 bulk into nanosheets-such as MoSe2, WSe2, MoS2, and WS2 nanosheets-within a short time and at a low temperature (ca. 80 °C). Specifically, by utilizing active plasma that is generated with an asymmetric electrical field during the electrochemical reaction at the surface of the submerged cathode tip, we are able to achieve doping of nitrogen atoms, from the electrolytes, into the semiconducting 2H-MX2 structures during their exfoliation process from the bulk states, forming N-doped MX2. We selected N-doped MoS2 nanosheets for demonstrating their catalytic hydrogen evolution potential. We modulated the electronic and transport properties of the MoS2 structure with the synergy of nitrogen doping and exfoliating for enhancing their catalytic activity. We found that the nitrogen concentration of 5.2 atom % at N-doped MoS2 nanosheets have an excellent catalytic hydrogen evolution reaction, where a low overpotential of 164 mV at a current density of 10 mA cm-2 and a small Tafel slope of 71 dec mV-1-much lower than those of exfoliated MoS2 nanosheets (207 mV, 82 dec mV-1) and bulk MoS2 (602 mV, 198 dec mV-1)-as well as an extraordinary long-term stability of >25 h in 0.5 M H2SO4 can be achieved.