Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction

Detalhes bibliográficos
Autor(a) principal: Gallo, Irã Borges Coutinho
Data de Publicação: 2018
Tipo de documento: Tese
Idioma: eng
Título da fonte: Repositório Institucional da UNESP
Texto Completo: http://hdl.handle.net/11449/153370
Resumo: Carbon supported PdAu nanoparticles with different Au contents (20-50% in atoms) were synthesized using a procedure carried out in a liquid two-phase system. As-prepared materials presented similar average particle diameter (~3nm) with narrow distribution over the carbon support, as shown by Transmission Electronic Microscopy (TEM). The combined data from X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) suggest that nanoparticles had Pd-enriched surfaces and Au-rich interiors. Cyclic Voltammetry (CVs) studies in H2SO4 further reinforced these findings, confirming that the nanoparticle surfaces were enriched with Pd. Moreover, XPS results show that increasing the Au content of PdAu alloys leads to varying amounts of surface-like and bulk-like Pd oxide, with a significant increase of metallic Pd. This result is consistent with data of X-ray Absorption Spectroscopy (XAS) around Pd L3 edge, which revealed that Au promotes an increase in the electronic occupancy of the Pd 4d band. Therefore, this whole set of characterizations suggests that the presence of Au in PdAu nanoalloys decreases the Pd affinity for oxygen, giving Pd a more noble-like character. In addition, the influence of ligand and ensemble effects on electrochemical surface processes, such as oxide formation/reduction, CO oxidation and hydrogen adsorption were also investigated. This was also a necessary step in order to determine the best technique to measure the Electrochemical Active Area (EAA) of Pd. The, electrocatalytic activity toward the Oxygen Reduction Reaction (ORR) was evaluated using a rotating ring-disk electrode in O2 saturated H2SO4 and KOH solutions. On acidic medium, increasing the Au content on PdAu nanoparticles lead to a consistent decrease in catalyst performance and a considerable increase in H2O2 production, suggesting a 2-electron pathway for the ORR. In contrast, on alkaline solution the PdAu 50:50 presented by far the best catalytic activity and the lowest production of H2O2, suggesting a 4-electron pathway for the ORR. Accelerated stability tests were also performed in both electrolytes. On acidic medium, the presence of Au seems to increase the rate of Pd dissolution. That was also observed in alkaline medium. In summary, in acidic medium, as ORR catalysts, PdAu nanoparticles were overall worse than pure Pd. However, in alkaline medium, the PdAu materials were not only better catalyst than pure Pd, but also the PdAu 50:50 surpassed Pt, proving to be a promising catalyst for use in alkaline fuel cells.
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spelling Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reactionPropriedades eletrônicas e estruturais de nanopartículas de PdAu/C e seu comportamento catalítico para a redução eletroquímica do oxigênioBimetalic catalystsPalladiumGoldOxygen reduction reationElectrocatalysisNanoparticlesFuel cellCatalisadores bimetálicosPaládioOuroReação de redução de oxigênioEletrocatáliseNanopartículasCélula de combustívelCarbon supported PdAu nanoparticles with different Au contents (20-50% in atoms) were synthesized using a procedure carried out in a liquid two-phase system. As-prepared materials presented similar average particle diameter (~3nm) with narrow distribution over the carbon support, as shown by Transmission Electronic Microscopy (TEM). The combined data from X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) suggest that nanoparticles had Pd-enriched surfaces and Au-rich interiors. Cyclic Voltammetry (CVs) studies in H2SO4 further reinforced these findings, confirming that the nanoparticle surfaces were enriched with Pd. Moreover, XPS results show that increasing the Au content of PdAu alloys leads to varying amounts of surface-like and bulk-like Pd oxide, with a significant increase of metallic Pd. This result is consistent with data of X-ray Absorption Spectroscopy (XAS) around Pd L3 edge, which revealed that Au promotes an increase in the electronic occupancy of the Pd 4d band. Therefore, this whole set of characterizations suggests that the presence of Au in PdAu nanoalloys decreases the Pd affinity for oxygen, giving Pd a more noble-like character. In addition, the influence of ligand and ensemble effects on electrochemical surface processes, such as oxide formation/reduction, CO oxidation and hydrogen adsorption were also investigated. This was also a necessary step in order to determine the best technique to measure the Electrochemical Active Area (EAA) of Pd. The, electrocatalytic activity toward the Oxygen Reduction Reaction (ORR) was evaluated using a rotating ring-disk electrode in O2 saturated H2SO4 and KOH solutions. On acidic medium, increasing the Au content on PdAu nanoparticles lead to a consistent decrease in catalyst performance and a considerable increase in H2O2 production, suggesting a 2-electron pathway for the ORR. In contrast, on alkaline solution the PdAu 50:50 presented by far the best catalytic activity and the lowest production of H2O2, suggesting a 4-electron pathway for the ORR. Accelerated stability tests were also performed in both electrolytes. On acidic medium, the presence of Au seems to increase the rate of Pd dissolution. That was also observed in alkaline medium. In summary, in acidic medium, as ORR catalysts, PdAu nanoparticles were overall worse than pure Pd. However, in alkaline medium, the PdAu materials were not only better catalyst than pure Pd, but also the PdAu 50:50 surpassed Pt, proving to be a promising catalyst for use in alkaline fuel cells.Nanopartículas de PdAu suportadas em carbono com diferentes frações de Au (20-50% em átomos) foram sintetizadas em um sistema líquido de duas fases. As nanopartículas preparadas apresentaram diâmetro médio próximo a 3 nm, com uma distribuição homogênea sobre o suporte de carbono, o que foi demonstrado por microscopia eletrônica de transmissão (TEM). O conjunto dos dados coletados por difração de raios X (XRD) e por espetroscopia de fotoelétrons excitados por raios X (XPS) demonstrou que o interior das nanopartículas é enriquecido por Au, enquanto a superfície é mais rica em Pd. A análise por XPS também demonstrou que o aumento da fração de Au nas ligas de PdAu leva a uma variação na fração de diferentes espécies de óxidos de Pd e um aumento na quantidade total de Pd metálico. Este resultado é consistente com aquele obtido por espectroscopia de absorção de raios-X (XAS), realizada na borda L3 do Pd, a qual revelou que o Au promove um preenchimento eletrônico na banda 4d do Pd. Ou seja, a presença do Au parece diminuir a afinidade do Pd pelo oxigênio. Ademais, foram estudados a influência de efeitos eletrônicos e do arranjo superficial de átomos sobre os processos eletroquímicos de formação/redução de óxidos, oxidação de CO adsorvido e adsorção de hidrogênio. Estes estudos também permitiram a determinação da área eletroquímica ativa de Pd. Por meio de todas estas caracterizações foi possível traçar correlações entre a composição no cerne das nanopartículas de PdAu e suas propriedades superficiais. A atividade catalítica para a reação de redução do oxigênio (RRO) foi avaliada utilizando-se a técnica do eletrodo de disco-anel rotatório, em soluções de H2SO4 e KOH saturadas com O2. Em meio ácido, o aumento da fração de Au levou a uma consistente queda de atividade e a um aumento na produção de H2O2, indicando predominância do mecanismo via 2 elétrons para a RRO. Em contraste, em meio alcalino o aumento da fração de Au levou a um significativo aumento na atividade catalítica, sendo predominante o mecanismo via 4 elétrons. Testes de estabilidade também foram realizados. Em meio ácido, a presença do Au parece aumentar ainda mais a taxa de dissolução do Pd. Isto também foi observado em meio alcalino, porém em menor intensidade. Em resumo, em meio ácido, os materiais de PdAu tiveram desempenho inferior ao Pd. Porém, em meio alcalino os materiais de PdAu não só tiveram um melhor desempenho que o Pd puro, mas o PdAu 50:50 chegou a ultrapassar a atividade catalítica da Pt, provando-se ser um catalisador promissor para aplicações em células a combustível alcalinas.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CNPq: 142497/2013-4Universidade Estadual Paulista (Unesp)Villullas, Hebe de las Mercedes [UNESP]Universidade Estadual Paulista (Unesp)Gallo, Irã Borges Coutinho2018-04-04T17:35:34Z2018-04-04T17:35:34Z2018-03-14info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/doctoralThesisapplication/pdfapplication/pdfhttp://hdl.handle.net/11449/15337000089927333004030072P8enginfo:eu-repo/semantics/openAccessreponame:Repositório Institucional da UNESPinstname:Universidade Estadual Paulista (UNESP)instacron:UNESP2023-11-23T06:10:46Zoai:repositorio.unesp.br:11449/153370Repositório InstitucionalPUBhttp://repositorio.unesp.br/oai/requestopendoar:29462024-08-05T18:29:00.441749Repositório Institucional da UNESP - Universidade Estadual Paulista (UNESP)false
dc.title.none.fl_str_mv Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
Propriedades eletrônicas e estruturais de nanopartículas de PdAu/C e seu comportamento catalítico para a redução eletroquímica do oxigênio
title Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
spellingShingle Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
Gallo, Irã Borges Coutinho
Bimetalic catalysts
Palladium
Gold
Oxygen reduction reation
Electrocatalysis
Nanoparticles
Fuel cell
Catalisadores bimetálicos
Paládio
Ouro
Reação de redução de oxigênio
Eletrocatálise
Nanopartículas
Célula de combustível
title_short Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
title_full Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
title_fullStr Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
title_full_unstemmed Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
title_sort Surface structure and electronic properties of carbon supported PdAu nanoparticles and their catalytic behavior toward the oxygen reduction reaction
author Gallo, Irã Borges Coutinho
author_facet Gallo, Irã Borges Coutinho
author_role author
dc.contributor.none.fl_str_mv Villullas, Hebe de las Mercedes [UNESP]
Universidade Estadual Paulista (Unesp)
dc.contributor.author.fl_str_mv Gallo, Irã Borges Coutinho
dc.subject.por.fl_str_mv Bimetalic catalysts
Palladium
Gold
Oxygen reduction reation
Electrocatalysis
Nanoparticles
Fuel cell
Catalisadores bimetálicos
Paládio
Ouro
Reação de redução de oxigênio
Eletrocatálise
Nanopartículas
Célula de combustível
topic Bimetalic catalysts
Palladium
Gold
Oxygen reduction reation
Electrocatalysis
Nanoparticles
Fuel cell
Catalisadores bimetálicos
Paládio
Ouro
Reação de redução de oxigênio
Eletrocatálise
Nanopartículas
Célula de combustível
description Carbon supported PdAu nanoparticles with different Au contents (20-50% in atoms) were synthesized using a procedure carried out in a liquid two-phase system. As-prepared materials presented similar average particle diameter (~3nm) with narrow distribution over the carbon support, as shown by Transmission Electronic Microscopy (TEM). The combined data from X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) suggest that nanoparticles had Pd-enriched surfaces and Au-rich interiors. Cyclic Voltammetry (CVs) studies in H2SO4 further reinforced these findings, confirming that the nanoparticle surfaces were enriched with Pd. Moreover, XPS results show that increasing the Au content of PdAu alloys leads to varying amounts of surface-like and bulk-like Pd oxide, with a significant increase of metallic Pd. This result is consistent with data of X-ray Absorption Spectroscopy (XAS) around Pd L3 edge, which revealed that Au promotes an increase in the electronic occupancy of the Pd 4d band. Therefore, this whole set of characterizations suggests that the presence of Au in PdAu nanoalloys decreases the Pd affinity for oxygen, giving Pd a more noble-like character. In addition, the influence of ligand and ensemble effects on electrochemical surface processes, such as oxide formation/reduction, CO oxidation and hydrogen adsorption were also investigated. This was also a necessary step in order to determine the best technique to measure the Electrochemical Active Area (EAA) of Pd. The, electrocatalytic activity toward the Oxygen Reduction Reaction (ORR) was evaluated using a rotating ring-disk electrode in O2 saturated H2SO4 and KOH solutions. On acidic medium, increasing the Au content on PdAu nanoparticles lead to a consistent decrease in catalyst performance and a considerable increase in H2O2 production, suggesting a 2-electron pathway for the ORR. In contrast, on alkaline solution the PdAu 50:50 presented by far the best catalytic activity and the lowest production of H2O2, suggesting a 4-electron pathway for the ORR. Accelerated stability tests were also performed in both electrolytes. On acidic medium, the presence of Au seems to increase the rate of Pd dissolution. That was also observed in alkaline medium. In summary, in acidic medium, as ORR catalysts, PdAu nanoparticles were overall worse than pure Pd. However, in alkaline medium, the PdAu materials were not only better catalyst than pure Pd, but also the PdAu 50:50 surpassed Pt, proving to be a promising catalyst for use in alkaline fuel cells.
publishDate 2018
dc.date.none.fl_str_mv 2018-04-04T17:35:34Z
2018-04-04T17:35:34Z
2018-03-14
dc.type.status.fl_str_mv info:eu-repo/semantics/publishedVersion
dc.type.driver.fl_str_mv info:eu-repo/semantics/doctoralThesis
format doctoralThesis
status_str publishedVersion
dc.identifier.uri.fl_str_mv http://hdl.handle.net/11449/153370
000899273
33004030072P8
url http://hdl.handle.net/11449/153370
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33004030072P8
dc.language.iso.fl_str_mv eng
language eng
dc.rights.driver.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
application/pdf
dc.publisher.none.fl_str_mv Universidade Estadual Paulista (Unesp)
publisher.none.fl_str_mv Universidade Estadual Paulista (Unesp)
dc.source.none.fl_str_mv reponame:Repositório Institucional da UNESP
instname:Universidade Estadual Paulista (UNESP)
instacron:UNESP
instname_str Universidade Estadual Paulista (UNESP)
instacron_str UNESP
institution UNESP
reponame_str Repositório Institucional da UNESP
collection Repositório Institucional da UNESP
repository.name.fl_str_mv Repositório Institucional da UNESP - Universidade Estadual Paulista (UNESP)
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