The influence of the local atomic packing of thin MoS$_{x}$ films on their electrocatalytic properties in hydrogen reduction

We have studied the characteristics of the structure, composition, and electrocatalytic properties of thin MoS$_{x}$ films obtained by pulsed laser deposition using an Mo target ablated in H$_2$S reactive-gas medium. The laser plume during deposition was directed tangentially and normally to the substrate, which allowed amorphous films to be obtained with different local atomic packings in an amorphous matrix consisting of Mo$_3$–S clusters. It is established that the orientation of Mo$_3$–S clusters influences charge transport in the catalyst and determines the type and surface density of catalytically active sites in the reaction of hydrogen evolution. For small, approximately equal amounts of Mo and Pt ($\sim$4 $\mu$g/cm$^2$) laser-deposited on glassy carbon substrates, the MoS$_{x}$ films were inferior to a Pt film with respect to hydrogen overvoltage (by about 90 mV) in acid solution, but the efficiency of thin-film MoS$_{x}$ catalysts at elevated cathode potentials exceeded that of a thin Pt film.