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Slim Moly S makes hydrogen: Layer dependent electrocatalysis in hydrogen evolution reaction with individual MoS2 nanodevices
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. University of Washington.
2018 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Slanka Moly S gör väte : Lagerberoende elektrokatalys vid generering av väte med individuella MoS2 nanoenheter. (Swedish)
Abstract [en]

Molybdenum disulfide (MoS2) has been demonstrated to be a potential catalyst in the hydrogen evolution reaction (HER). Due to its highly active edge site, abundance, and low cost, it rivals Pt. However, the potential activity of the MoS2 basal plane has largely been ignored. The physical characteristics of MoS2 and its corresponding band structure change significantly with decreasing thickness, especially at the monolayer limit. Thus, an investigation on the thickness dependence may provide important insights into the MoS2 basal plane activity.

In this thesis, the layer dependent electrocatalytic performance is investigated with mono-, bi- and multilayer MoS2 based individual nanodevices. Three conclusions were reached. (1) Monolayers showed exchange current densities more than one order of magnitude higher than that of the multilayers, 0.12 mA/cm2 and 8.7 mA/cm2, respectively. Furthermore, the onset potential of the monolayer was several hundred millivolts lower than that of the multilayer, about 0.2 V vs RHE for the monolayer versus 0.5 V vs RHE for the multilayer. The Tafel slope of 100-200 mV/dec revealed that the rate limiting step was the adsorption of hydrogen. (2) Interestingly, the bilayer sample exhibited an increase in its exchange current density from 0.3 mA/cm2 to 8 mA/cm2 when cycled extensively. This is suspected to be caused by intercalation of hydrogen between the atomic layers. (3) Additionally, the back-gate voltage is applied to tune the Fermi level of the material and the catalytic performance. It was found that the back-gate voltage induces an irreversible change in all samples, increasing the exchange current density by an order of magnitude.

The superior basal plane performance of the monolayers to that of the multilayers reveals a new way to optimize the performance of MoS2 as a HER catalyst. In addition, the results above illuminate the yellow brick road to potential improvements in other layered materials as well.

Place, publisher, year, edition, pages
2018. , p. 46
Series
UPTEC Q, ISSN 1401-5773 ; 18018
Keywords [en]
MoS2, hydrogen evolution reaction, HER, Electrocatalysis, nanodevice
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-355025OAI: oai:DiVA.org:uu-355025DiVA, id: diva2:1223608
External cooperation
University of Washington
Subject / course
Material
Educational program
Master Programme in Materials Engineering
Supervisors
Examiners
Available from: 2018-06-26 Created: 2018-06-25 Last updated: 2018-06-26Bibliographically approved

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