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# Size-selected molybdenum disulfide clusters for hydrogen evolution

Cuddy, Martin (2014)
Ph.D. thesis, University of Birmingham.

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## Abstract

In this work, size-selected molybdenum disulfide (MoS$$_2$$) nanoclusters were produced using a magnetron sputter source and time-of-flight mass filter. Magnetron sputtering is a common industrial method for preparation of MoS$$_2$$ thin films. The combination of this technology with accurate size control allows us to produce, in high vacuum, lab-scale quantities of size-selected clusters. The strong spatial confinement effects in MoS$$_2$$ suggests that such control will modify the catalytic properties. This method also has potential to enhance MoS$$_2$$ performance in areas such as hydrodesulfurisation, intercalation batteries and tribology; as well as elucidating the dynamics of compound formation in the gas-phase.

Structural properties of these MoS$$_2$$ clusters are studied using aberration-corrected STEM. The optimum catalytic size range of 1-5nm has not previously been studied in detail for gas phase synthesis. This work bridges the gap in the cluster beam literature between small, few atom clusters and the production of large MoS$$_2$$ fullerenes and monolayers.

It has been found that MoS$$_2$$ clusters display a characteristic layered structure down to the smallest studied cluster, 50 units of MoS$$_2$$. Growth of clusters is indicative of anisotropic growth from the reactive edge sites, proceeds by subsequent addition of van der Waals bound layers and finally coalescence of smaller units in the case of large clusters. The electrocatalytic properties of these clusters are explored by cyclic voltammetry and show good activity for the Hydrogen Evolution Reaction despite the presence of surface oxides. The reaction current normalised matches to loading matches some of the best catalysts produced to date.

Type of Work: Ph.D. thesis. Rees, Neil and Palmer, Richard E. Colleges (2008 onwards) > College of Engineering & Physical Sciences Chemical Engineering TP Chemical technology University of Birmingham 5210
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