Electrochemical Formation of Amorphous Molybdenum Phosphosulfide for Enabling the Hydrogen Evolution Reaction in Alkaline and Acidic Media

The formation of a nonprecious metal catalyst that is active for the hydrogen evolution reaction (HER) over a wide pH range is of particular interest. In this work, a mixed anion electrocatalyst, namely, amorphous molybdenum phosphosulfide films containing oxygen were produced via a simple electrochemical process allowing the composition and morphology of the film to be controlled. The catalyst shows a homogeneous distribution of Mo, S, P, and O with a high number of active sites due to its amorphous state. (NH4)2MoS4 was used as a molybdenum and sulfur source, while NaPO2H2 was used as the phosphorus source. Thiourea was also investigated as an additional sulfur source during the electrodeposition process. The electrocatalyst was active for the HER in acidic media as expected, but showed excellent performance in alkaline media where Tafel slope values of 36 and 122 mV dec–1 were recorded, respectively. In addition, the electrocatalyst demonstrated long-term stability in both media for several hours. The materials were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and their physicochemical properties correlated to their electrocatalytic activity for the HER.