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A Computational Screening of Supported Metal Films

Yates, JLR; (2016) A Computational Screening of Supported Metal Films. Doctoral thesis , UCL (University College London). Green open access

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Abstract

This thesis presents the results of first-principles Density Functional Theory (DFT) calculations of Pt-carbide and tie-layered carbide systems in an effort to produce computational screening methods for industrial application. The agglomeration of Pt and PGM catalytic materials on supports leads to loss of surface area and diminished activity towards the industrial processes being targeted. In this work, we have explored the possibility of using carbides as cores for core-shell nanoparticles as a means to thrift Pt loading, promote Pt availability and increase catalyst activity towards the Oxygen Reduction Reaction (ORR) present in hydrogen fuel cells. For our initial dataset 6 carbides were selected for theoretical investigation; TiC, SiC-β, NbC, TaC and hexagonal and cubic WC. Pt overlayers were then adsorbed on to the carbides and detailed analysis of the resultant electronic structures made in order to identify carbide characteristics which predict good Pt adsorption. WC and SiC were calculated to allow full Pt encapsulation whilst the fcc carbides experienced limited Pt adsorption. Since full encapsulation of the catalyst core is crucial for Pt availability and both core and shell stability, other metallic layers were also trialled in an effort to promote Pt adsorption. These metals were observed to offer different levels of stability with respect to the Pt forming the outer surface layer although Pt introduction on to previously unfavourable carbide facets is theoretically possible using this method. The activity of the Pt overlayers towards ORR was then assessed via the study of O adsorption energies, revealing that several of the Pt/carbide structures are indeed predicted to produce ‘Pt-like’ or weakened O adsorption strengths which should maintain or promote ORR activity with the use of much less Pt. Finally, the stability of the Pt overlayers towards agglomeration was considered. Pt cluster calculations were carried out in order to investigate the effect on electronic structure of cluster size and geometry. These results were then used to assess the strength of Pt hemispheres interactions at the carbide surface. A thermodynamic model was also developed to enable the prediction of Pt overlayer structures under differing conditions and form the basis for entropic corrections to be made in overlayer-cluster comparisons.

Type: Thesis (Doctoral)
Title: A Computational Screening of Supported Metal Films
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1476042
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