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Surface activation of graphene nanoribbons for oxygen reduction reaction by nitrogen doping and defect engineering: An ab initio study
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0002-3881-6764
Umeå University, Faculty of Science and Technology, Department of Physics.ORCID iD: 0000-0001-9239-0541
2018 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 137, p. 349-357Article in journal (Refereed) Published
Abstract [en]

Introducing heteroatoms and creating structural defects on graphene is a common and rather successful strategy to transform its inert basal plane into an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR). However, the intricate atomic configuration of defective graphenes difficult their optimization as ORR electrocatalysts, where not only a large density of active sites is desirable, but also excellent electrical conductivity is required. Therefore, we used density functional theory to investigate the current-voltage characteristics and the catalytic active sites towards ORR of nitrogen-doped and defective graphene by using 8 zig-zag graphene nanoribbons as model systems. Detailed ORR catalytic activity maps are created for ten different systems showing the distribution of catalytic hot spots generated by each defect. Subsequently, the use of both current-voltage characteristics and catalytic activity maps allow to exclude inefficient systems that exhibit either low electrical conductivity or have adsorption energies far from optimal. Our study highlights the importance of considering not only the interaction energy of reaction intermediates to design electrocatalysts, but also the electrical conductivity of such configurations. We believe that this work is important for future experimental studies by providing insights on the use of graphene as a catalyst towards the ORR reaction. 

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 137, p. 349-357
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Condensed Matter Physics
Identifiers
URN: urn:nbn:se:umu:diva-151037DOI: 10.1016/j.carbon.2018.05.050ISI: 000440661700035Scopus ID: 2-s2.0-85047971117OAI: oai:DiVA.org:umu-151037DiVA, id: diva2:1245351
Available from: 2018-09-05 Created: 2018-09-05 Last updated: 2024-07-02Bibliographically 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, JoakimBoulanger, NicolasGracia-Espino, Eduardo

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