In this work, we use a combination of cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and density functional theory (DFT) calculations to investigate the catalytically active sites and structural evolution of MoSx films during the electrochemical hydrogen evolution reaction (HER). Aqueous 1 M HClO4 was used as the electrolyte. We found, using XPS and operando Raman spectroscopy, that anodically deposited MoSx(x≈3) transformed to a structure with MoS2 composition during the cathodic sweep of a CV. A Raman peak at 2530 cm-1 was recorded at potentials relevant to HER, which we ascribed to the S-H stretching vibration of MoSx-H moieties. This assignment was corroborated by H/D isotope exchange experiments. Mo-H (or Mo-D) stretching vibrations were not observed, which thus allowed us to rule out Mo centers as catalytic sites for proton reduction to H2. DFT calculations were performed on a variety of MoSx structures and corroborated the assignments of the observed vibrational frequencies. Based on these experimental measurements and quantum chemical simulations, we propose that the sulfur atoms in amorphous MoSx are the catalytically active sites for evolving H2.

Identification of sulfur atoms as catalytically active sites for proton reduction on amorphous molybdenum sulfide

253rd National Meeting (2017)

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