Journal
ACS CATALYSIS
Volume 6, Issue 2, Pages 861-867Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.5b02369
Keywords
amorphous molybdenum sulfide; hydrogen evolution reaction; electrocatalysis; linear sweep voltammetry; X-ray photoelectron spectroscopy; density functional theory
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Funding
- National University of Singapore [R143-000-515-133, R-143-000-587-112]
- U.S. Office of Naval Research [N00014-15-1-2223]
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The catalytic activities of sulfur sites in amorphous MoSx for the electrochemical hydrogen evolution reaction (HER) was investigated in aqueous 0.5 M H2SO4 electrolyte. Using X-ray photoelectron spectroscopy and linear sweep voltammetry, we found the turnover frequency for H-2 production to increase linearly with the percentage of S atoms with higher electron binding energies. These S atoms could be apical S2- and/or bridging S-2(2-). To distinguish the catalytic performances of these two types of atoms, we turn to quantum chemical simulations using density functional theory. The apical S2- atoms were found to adsorb H weakly with a Gibbs free energy for atomic H adsorption (Delta G(H)) in excess of +1 eV, and were thus ruled out as reaction sites for HER. In situ Raman spectroscopy of the model [Mo3S13](2-) cluster further demonstrate the higher catalytic reactivity of the bridging S-2(2-) over terminal S-2(2-) (which have lower electron binding energy) for proton reduction.
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