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Samuel, N., 2020. Computational pathways to higher efficiency solid oxide fuel cells: a first principle description of Cu/CeO2(111) and β-doped-Cu/CeO2(111) nanocomposites. PhD, Nottingham Trent University.
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Abstract
This work uses Ab initio DFT calculations to model a novel bulk Cu/CeO2(111) nanocomposite and studies the characteristic and microscopic properties of the material at the surface and interface. The results reported herein shows a nanocomposite Cu/CeO2(111) material simulated from an over-layer of a p(1x3) Cu nanorod along the [-1 ½ ½ ] plane of a p(3x2) CeO2(111) slab with upto 6 O-Ce-O triple layers. LDA+U (U = 6 eV on Ce only) gives a 0.38% lattice mismatch (0.01% difference from the 0.37% experimental lattice parameter mismatch) and very small strain that allows for a 3:2 Cu:CeO2(111) lattice match. The LDA+U binding energy of Cu for a four-layer stripe on ceria is 1.72 ev/Cu and interface energy of ~0.180 eV/Å2. Layer-by-layer Cu-stripe model optimisation shows >3 layers of Cu is required for the Cu to adopt a bulk-like structure on the ceria. Less than four layers of Cu tends to buckle, while a monolayer planar adsorption of Cu on ceria buckles into tetrahedral like Cu structures on the CeO2(111). The PDOS study of the interaction between Cu and ceria shows a characteristic Cu binding peak within the -1.0 eV to 1.0 eV gap state of ceria, suggesting an orbital interaction between Cu 3d and ceria Ce 4f orbital. Adhesion of the Cu stripe on the ceria slab results in charge transfer from CU to the Ce and the formation of many Ce3+ polarons. The polaronic effect at the interface and the characteristic features of this model suggests that; for Nth number of Ce in p(3x2) CeO2(111), 1/2Nth number of localised Ce3+ is required to saturate the ceria surface. Concentration of Ce3+ polaron > 6 per p(3x2) surface results in concentrated polarons and weaker Ce-O bonds which cleave to form oxygen vacancies. The S-species tolerance (efficiency test) using S and H2S interaction on Cu/CeO2(111), shows preferential adsorption of S and H2S on the Cu stripe, but closer to the interface itself where there is low coordination Cu atoms. H2S and S respectively stabilise at the bridge (~1.30 – 1.40 eV) and hollow Cu (~2.43 eV) sites. Bulk Cu/CeO2(111) material interface catalyses the split of H2S into component SH+H and S+H+H fragments, while re-adsorbing the S-moiety at the Cu stripe, the H atom forms extended hydrogen bonds at the ceria component. Reported herein also are functional β-doped-Cu/CeO2(111) with low and high defect formation energies. H2S interaction with the β-doped-Cu/CeO2(111) analogue shows a gain in sulphur tolerance relative to Cu/CeO2(111) for β = Ta (>14%); Rh(~6.8%); Fe (~6.0%); and Co(~6.0%). Formation of Ta-doped-Cu/CeO2(111), follows an exothermic pathway (-2.53 eV). The sulphur tolerance behaviour of Cu/CeO2 and the high gain in tolerance when doped with Ta, demonstrate the potential for the use of Cu/CeO2, and Ta-doped-Cu/CeO2 as future SOFC anodes with reduced susceptibility to sulphur poisoning. The bulk Cu/CeO2(111) and β-doped-Cu/CeO2(111) analogues are interesting materials with impressive properties that could be harnessed for use in green technologies and application.
| Item Type: | Thesis |
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| Creators: | Samuel, N. |
| Date: | March 2020 |
| Rights: | This doctoral research work as carried out by the author in the school of science and technology, Nottingham Trent University, is an intellectual property of the author and maybe owned by the research sponsor(s) and the Nottingham Trent University. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of information contained within this document should be fully referred, quoting the author, tittle, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed in the owners of the Intellectual Property Rights. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Linda Sullivan |
| Date Added: | 21 Jun 2023 13:32 |
| Last Modified: | 21 Jun 2023 13:33 |
| URI: | https://irep.ntu.ac.uk/id/eprint/49244 |
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