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Theoretical Analysis of Surface Active Sites in Defective 2H and 1T ' MoS2 Polymorphs for Hydrogen Evolution Reaction: Quantifying the Total Activity of Point Defects
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0001-9239-0541
2020 (English)In: Advanced Theory and Simulations, E-ISSN 2513-0390, Vol. 3, no 3, article id 1900213Article in journal (Refereed) Published
Abstract [en]

Defect engineering is a common and promising strategy to improve the catalytic activity of layered structures such as MoS2, where in particular the 2H and 1T ' polymorphs have been under intense study for their activity toward the hydrogen evolution reaction. However, the large variety of defects, each with its own distinct and usually unknown effects, complicates the design and optimization of such defective materials. Therefore, it is relevant to characterize in detail the effect of individual defects and to be able to combine these observations to describe more complex materials, such as those seen experimentally. Therefore, nine point defects (antisites defects and vacancies) are theoretically studied on single layer 1T, 1T ', and 2H MoS2 polymorphs, and the variation and spatial distribution in the active sites are identified. It is found that all defective 1T ' monolayers exhibit an increase in the exchange current density of at least 2.3 times when compared to pristine 1T ' MoS2, even if a reduced number of active sites are observed. The results are later used to propose a methodology to study materials containing a mixture of crystal phases, or other alterations that cause inhomogeneous changes in the activity of catalytic sites.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2020. Vol. 3, no 3, article id 1900213
Keywords [en]
density functional theory, hydrogen evolution reaction, molybdenum disulfide, point defects, transition metal chalcogenides
National Category
Condensed Matter Physics Materials Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-168157DOI: 10.1002/adts.201900213ISI: 000508585100001Scopus ID: 2-s2.0-85081036235OAI: oai:DiVA.org:umu-168157DiVA, id: diva2:1415328
Available from: 2020-03-18 Created: 2020-03-18 Last updated: 2023-03-24Bibliographically approved
In thesis
1. Electrocatalysts for sustainable hydrogen energy: disordered and heterogeneous nanomaterials
Open this publication in new window or tab >>Electrocatalysts for sustainable hydrogen energy: disordered and heterogeneous nanomaterials
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the current global greenhouse gas emissions, our remaining carbon budget is depleted in only 7 years. After that, several biophysical systems are predicted to collapse such as the arctic ice, coral reefs and the permafrost, leading to potentially irreversible consequences. Our emissions are strongly correlated to access of energy and even if we are aware of the planetary emergency today, our emissions still continue to grow. Electrical vehicles have the possibility to reduce the emissions in the transportation sector significantly. However, these vehicles are still expensive and impractical for long-distance or heavy transportation. While political actions and technological development are essential to keep prices down, the driving dis- tance can be increased by replacing the batteries for onboard electricity production. 

In hydrogen fuel cells, electricity is produced by combining hydrogen gas (H2) and oxygen with only water as the by-product and if employed in electrical vehicles, distances of 500 km are enabled with a refueling time in 5 minutes. For other uses than in vehicles, H2 is also promising for large-scale electricity storage and for several industrial processes such as manufacturing CO2-free steel, ammonia and synthetic fuels. However, today most H2 production methods relies on fossil fuels and releases huge amounts of CO2. 

Electrolysis of water is an alternative production method where H2, along with oxygen are produced from water. To split the water, electricity has to be added and if renewable energy sources are used, the method has zero emissions and is considered most promising for a sustainable hydrogen energy economy. The tech- nique is relatively expensive compared to the fossil fuel-based methods and relies on rare noble metals such as platinum as catalysts for decreasing the required energy to split water. For large scale productions, these metals need to be replaced by more sustainable and abundant catalysts to lower the cost and minimize the environmental impacts. 

In this thesis we have investigated such candidates for the water splitting reaction but also to some extent for the oxygen reduction reaction in fuel cells. By combining theory and experiments we hope to aid in the development and facilitate a transition to clean hydrogen energy. We find among other things that i) defects in catalytic materials plays a significant role the performance and efficiency, and that ii) heterogeneity influence the adsorption energies of reaction intermediates and hence the catalytic efficiency and iii) while defects are not often studied for electrocatalytic reactions, these may inspire for novel materials in the future. 

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2021. p. 88
Keywords
Water splitting, Electrochemistry, Nanomaterials, Density functional theory, Hydrogen evolution, MoS2, Fuel cell
National Category
Condensed Matter Physics
Research subject
nanomaterials; Physics; Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-180130 (URN)978-91-7855-482-9 (ISBN)978-91-7855-481-2 (ISBN)
Public defence
2021-03-11, BIO.A.206 – Aula Anatomica, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2021-02-18 Created: 2021-02-15 Last updated: 2021-02-16Bibliographically approved

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Ekspong, JoakimGracia-Espino, Eduardo

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