Surface plasma–induced tunable nitrogen doping through precursors provides 1T-2H MoSe2/graphene sheet composites as electrocatalysts for the hydrogen evolution reaction

In this paper we present that the surface plasma-induced tunable nitrogen doping that requires short processing time at low temperature through various nitrogen precursors that converted the 2H phase into a coexisting 1T-2H phase in the MoSe2 nanosheets; subsequently combining the N-doped MoSe2 with graphene sheets (G) for synthesis of N-doped 1T-2H MoSe2/G composites (N-MoSe2/G) for the hydrogen evolution reaction (HER). We found that the amount of the 1T phase in the MoSe2 nanosheets can be tuned by selecting suitable N-atom precursors—such as NH4NO3, urea and melamine—with our method; moreover, the amount of the 1T phase of the composites induced increases with nitrogen doping concentration at low concentration range (Ca. 4.7%—7.3%) but decreased when the nitrogen doping is over 7.3%. Subsequently, after covering the N-MoSe2 with graphene sheets, the composites featuring highly active sites that facilitated the hydrogen evolution reaction (HER). As a result, the N-MoSe2/G composites exhibited a low overpotential of 153 mV at a current density of 10 mA/cm2 and a Tafel slope of 67 mV/dec, much better than those of undoped-MoSe2 (252 mV, 123 mV/dec) and the N-MoSe2 nanosheets (197 mV, 83 mV/dec). The N-MoSe2/G composites also functioned as a stable electrocatalyst, undergoing over 10,000 cycles of linear sweep voltammetry without degradation. Our approach to tunable nitrogen doping in MoSe2 nanosheets and forming composites provides a feasible way to produce electrocatalysts in mass-scale and low energy process with two-dimensional transition metal dichalcogenide materials.