X-ray photoelectron spectroscopy (XPS) was employed to analyze the metal valence states and electronic structures of HP-MoOC and HCP-MoOC catalysts. As displayed in Figure , the Mo 3d spectra for both HCP-MoOC and HP-MoOC are decomposed into 3d5/2 and 3d3/2 peaks because of the spin-orbital coupling feature HER electrocatalytic activities of the plasma-grown catalysts were evaluated using a three-electrode electrochemical configuration in a 0.5 M H2SO4 electrolyte. Figure shows that the plasma-grown MoOxCy catalysts significantly outperform the commercial MoO2 powders, and HCP-MoOC shows superior electrocatalytic performance to that of HP-MoOC.