Abstract
Hydrogen evolution reaction (HER) activities of self-assembled monolayers (SAMs) of [Mo3S7(S2CNMe2)3] and several other MoSx molecular clusters are presented on planer Au electrode. Our study suggests that such Mo-S clusters are unstable under HER reaction conditions of a strongly acidic electrolyte. The [Mo3S7(S2CNEt2)3]I monolayer prepared from DMF showed greater stability among all the studied precursors. The X-ray photoelectron spectroscopy (XPS) analysis on a monolayer of [Mo3S7(S2CNMe2)3]I in THF assembled on Au/ITO suggested sulfur-rich composition with S:Mo ratio of 2.278. The Mo-S monolayer clusters resulting from [Mo3S7(S2CNMe2)3]I in THF showed a Tafel slope of 75.74 mV dec−1 and required a lower overpotential of 410 mV to reach a high HER catalytic current density of 100 mA cm−2 compared to the other studied precursors. Surface coverage of the Mo-S clusters on the Au surface was confirmed by cyclic voltammetry (CV) curves from K3Fe(CN)6 and anodization of Au surface. Further, the rotating ring-disk electrode (RRDE) measurements were performed for the monolayer of [Mo3S7(S2CNMe2)3]I prepared in THF to study its reaction kinetics. The HER catalytic activity of such monolayer Mo-S clusters can further be improved by controlling the sulfur vacancy.
Highlights
Due to the adverse environmental effects of fossil fuels and their rapid decrease in availability, there is a growing demand for developing new clean and renewable energy resources
The rotating ring-disk electrode (RRDE) measurements were performed for the monolayer of [Mo3S7(S2CNMe2)3]I prepared in THF to study its reaction kinetics
The benefits of using a monolayer configuration instead of thin films of the Mo-S molecular characteristics are more likely to be retained than the results shown in Figure 2; and (3) there is no clusters include: (1) short distance for catalyzing proton reduction; (2) intrinsic mass transfer effect ofcharge moleculartransfer catalysts for proton reduction reaction in such heterogeneous system catalytic characteristics more likely tomolecular be retained than theforresults shown in Figure 2; and (3)
Summary
Due to the adverse environmental effects of fossil fuels and their rapid decrease in availability, there is a growing demand for developing new clean and renewable energy resources. Solar power could be a viable solution to this problem, as it is a readily available and abundant source of renewable energy [1]. One of the popular methods among various emerging power conversion technologies is photoelectrochemical (PEC) water splitting that utilizes solar energy alongside electrochemistry to split water to produce hydrogen-based fuels in solar-to-fuel devices [2]. PEC water splitting involves the following necessary steps: (1) absorption at the photocatalyst such that the photon energy absorbed is more than the band gap energy of the photocatalyst; (2) generation of photo-excited electron–hole pairs; (3) separation of these charges across the surface of the photocatalyst without recombination; and (4) reduction and oxidation of water by the photogenerated electrons and holes to produce H2 and O2 [3]. PEC water splitting can be challenging due to the need of thermodynamic potential of −1.23 V vs. RHE at least for the reaction to occur as Inorganics 2019, 7, 79; doi:10.3390/inorganics7060079 www.mdpi.com/journal/inorganics
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