Comparative Study of the Structure, Composition, and Electrocatalytic Performance of Hydrogen Evolution in MoS _{x ~2+δ}/Mo and MoS _{x~ 3+δ} Films Obtained by Pulsed Laser Deposition

Abstract

Systematic and in-depth studies of the structure, composition, and efficiency of hydrogen evolution reactions (HERs) in MoS _x films, obtained by means of on- and off-axis pulsed laser deposition (PLD) from a MoS ₂ target, have been performed. The use of on-axis PLD (a standard configuration of PLD) in a buffer of Ar gas, with an optimal pressure, has allowed for the formation of porous hybrid films that consist of Mo particles which support a thin MoS _{x ~2+δ} (δ of ~0.7) film. The HER performance of MoS _{x ~2+δ}/Mo films increases with increased loading and reaches the highest value at a loading of ~240 μg/cm ². For off-axis PLD, the substrate was located along the axis of expansion of the laser plume and the film was formed via the deposition of the atomic component of the plume, which was scattered in Ar molecules. This made it possible to obtain homogeneous MoS _{x ~3+δ} (δ~0.8–1.1) films. The HER performances of these films reached saturation at a loading value of ~163 μg/cm ². The MoS _{x ~3+δ} films possessed higher catalytic activities in terms of the turnover frequency of their HERs. However, to achieve the current density of 10 mA/cm ², the lowest over voltages were −162 mV and −150 mV for the films obtained by off- and on-axis PLD, respectively. Measurements of electrochemical characteristics indicated that the differences in the achievable HER performances of these films could be caused by their unique morphological properties.