A study of methanol electro-oxidation reactions in carbon membrane electrodes and structural properties of Pt alloy electro-catalysts by EXAFS

Page, Tameka; Johnson, Ryan S.; Hormes, J.; NODING, S. A.; Rambabu, B.

doi:10.1016/s0022-0728(00)00090-5

Cited by 124 publications

(70 citation statements)

References 18 publications

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“…Initially, research activities were focused on anode catalysts for DMFCs [19][20][21][22]. In the last years platinum alloy catalysts were investigated as cathode catalysts in PEFCs in order to improve the oxygen reduction reaction (ORR).…”

Section: Physical Characterization Of Carbon-supported Platinum Alloymentioning

confidence: 99%

Physical and electrochemical characterization of catalysts for oxygen reduction in fuel cells

et al. 2007

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The cathode catalysts in low temperature fuel cells are associated with major cell efficiency losses, because of kinetic limitations of the oxygen reduction reaction. Additionally, methanol oxidation at the cathode leads to significant lowering of the efficiency in direct methanol fuel cells, which can be alleviated by use of methanoltolerant catalysts. In this work, alternative carbon-supported platinum-alloy catalysts were investigated by physical methods. Second, methanol-tolerant rutheniumselenide catalysts were characterized by physical and electrochemical methods. Besides V-i characteristics and electrochemical impedance spectroscopy as electrochemical methods, physical methods such as X-ray photoelectron spectroscopy, nitrogen adsorption, porosimetry by mercury intrusion and temperature programmed reduction are used to characterize the catalysts. The electrochemical characterization yields information about properties and behavior of the catalyst. In contrast to platinum a significantly different hydrophobic behavior of the RuSe/C catalysts is found. Low open circuit voltage values measured for RuSe/ C indicate an effect on both electrodes. The anode reaction was also influenced by the different cathode catalysts. As a result of the formation of H 2 O 2 at the cathode, which passes through the membrane from cathode to anode side, a mixed anode potential is formed. By comparing RuSe/C catalysts before and after electrochemical stressing, changes of the catalysts are determined. Postmortem surface analysis (by X-ray photoelectron spectroscopy) revealed that catalyst composition and MEA structure changed during electrochemical stressing. During fuel cell operation selenium oxide is removed from the surface of the catalysts to a large extent. Additionally, a segregation effect of selenium in RuSe to the surface is identified.

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Section: Physical Characterization Of Carbon-supported Platinum Alloymentioning

confidence: 99%

Physical and electrochemical characterization of catalysts for oxygen reduction in fuel cells

et al. 2007

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“…Sn [49]; Pd, Sn [50]; Os [51]; Fe, Co, Ni, Cu [52]; Co [53] and Ni [54] or even tri-and tetrametallic systems [48,55,56]. However, the state-of-the-art option is Ru, which was introduced already in the 1960s [57] and is commonly used in commercial catalysts and as the standard catalyst in DMFC testing.…”

Section: Pt-based Catalysismentioning

confidence: 99%

Silicon nanograss as micro fuel cell gas diffusion layer

et al. 2010

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Direct methanol fuel cells (DMFC) produce electrical energy directly from chemical energy. They are a promising candidate for power sources of portable devices due to the high energy density of methanol and the quick recharging procedure by fuel insertion. However, the problem areas of the DMFC are the slow electro-oxidation of methanol and the permeated methanol reacting at the cathode. New catalysts are constantly searched but they are often tested only for catalytic activity and the DMFC testing is omitted even though the catalyst layer (CL) structure has a large impact on the performance. Miniaturization of the system is also necessary for portable applications. Silicon etching can be used to fabricate small structures for fuel cells replacing or enhancing the functions of laboratory-scale components.In the first part of this thesis, new catalysts for the DMFC are studied with the emphasis on the CL structure. Different carbon supports for the anode were studied: standard carbon black and alternative few-walled carbon nanotubes (FWCNT) and graphitized carbon nanofiber (GNF). The alternative supports showed better DMFC performance but their stability was lower than with carbon black. However, the CL formed with GNF showed a very porous structure enhancing the mass transfer, so that higher binder content could be used improving the stability to the level of carbon black and the performance by 30%. The FWCNTs were also investigated as a platform for enzymatic methanol oxidation by studying the electrochemical properties of an immobilized cofactor pyrroloquinoline quinone (PQQ). A large amount of PQQ was adsorbed having a strong redox response and good stability in a wide pH window. For the cathode, a methanol-tolerant, Pt-free nitrogen-doped FWCNTs were tested in an alkaline DMFC as such testing is not often made. Its performance was remarkably 4 times better than with Pt when synthetic air was used as the oxidant.In the second part of thesis, an integrated gas diffusion layer (GDL) consisting of Si nanoneedles (nanograss) was tested in a micro fuel cell (MFC). The layer functioned properly at low current densities. For high power applications, a standard carbon cloth GDL was tested with the nanograss as a contact surface reducing the resistance between the GDL and the flow field. The use of the nanograss improved the MFC performance and stability. Finally, the MFCs were used as a catalyst testing platform and the results were compared with a similar test in a laboratory-scale DMFC. The results varied showing that the DMFC components also have a large impact on catalyst testing.Keywords direct methanol fuel cell, carbon nanomaterials, micro fuel cells, catalyst layer Tiivistelmä Suorametanolipolttokennot (SMPK) tuottavat sähköenergiaa suoraan kemiallisesta energiasta. Ne ovat lupaava vaihtoehto kannettavien laitteiden voimanlähteeksi, koska metanolilla on korkea energiatiheys ja lataaminen tapahtuu nopeasti polttoainelisäyksellä. SMPK:lla on kuitenkin rajoitteina metanolin hidas hapetusreaktio ja katodi...

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“…Investigações usando espectroscopia de absorção de raios-X (XAS) [40][41][42][43] têm mostrado que é possível medir mudanças de natureza eletrônica (como vacâncias na banda 5-d da Pt) e nas interações atômicas de curto alcance (como a distância das ligações Pt-Pt e o número de coordenação) com especificidade elementar em condições in situ para vários tipos de sistemas eletroquímicos 43 . A aplicação da técnica XANES ("X-absorption near-edge structure") a ligas nanocristalinas de Pt-Co, Pt-V, Pt-Ru, Pt-Sn e Pt-Os suportadas em carbono tem mostrado que a associação de tais espécies interfere tanto na estrutura atômica como eletrônica da platina 40,[43][44][45][46][47][48] .…”

Section: Caracterização Dos Materiais Por Espectroscopia De Absorção unclassified

Eletrocatálise das reações de oxidação de hidrogênio e de redução de oxigênio

Ticianelli¹,

Câmara²,

Santos³

2005

Quím. Nova

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Recebido em 6/7/04; aceito em 3/11/04; publicado na web em 28/2/05 ELECTROCATALYSIS OF THE HYDROGEN OXIDATION AND OXYGEN REDUCTION REACTIONS. This work discusses the electrocatalytic processes taking place in the polymer electrolyte fuel cell electrodes, specifically the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR), because these are clear examples of electrochemical reactions favored by the use of electrocatalysts. Since the gaseous reactants are very little soluble in the electrolyte, the use of special electrodes, named gas diffusion electrodes, is required to promote easy and continuous access of reactant gases to the electrocatalytic sites. Besides this, other important aspects such as the use of spectroscopic techniques and of theoretical models to improve the knowledge of the electrocatalytic systems are shortly discussed.Keywords: electrocatalysis; hydrogen oxidation reaction; oxygen reduction reaction. INTRODUÇÃOO termo Eletrocatálise começou a ser difundido a partir da dé-cada de 60, na discussão da influência do material do eletrodo sobre a cinética da reação eletroquímica de desprendimento de hidrogênio. Nos dias de hoje, o uso do termo tornou-se muito mais abrangente, referindo-se genericamente ao efeito da natureza do material do eletrodo sobre a cinética de qualquer reação eletroquímica. Na maioria dos casos, o eletrodo não é transformado durante a ocorrência da reação, servindo apenas como um aceitador ou doador de elétrons e participando do processo através de etapas de adsorção de reagentes e/ou intermediários.Neste contexto, verifica-se que os fundamentos que governam as propriedades eletrocatalíticas têm muito em comum com aqueles da catálise heterogênea. Assim, diversos aspectos, muitos deles comuns à catálise heterogênea, governam os processos eletrocatalíticos: (1) a atividade eletrocatalítica é função da estrutura eletrônica dos átomos da superfície do material que compõe o eletrodo e (2) as propriedades superficiais, químicas e estruturais são fundamentais na definição da velocidade e do caminho da reação. Específico da eletrocatálise é o fato de que nos processos eletroquímicos estão sempre envolvidas reações de transferência de carga, sendo possível modificar a energia de ativação e/ou as propriedades da superfície ativa através do controle do potencial do eletrodo.Inúmeras reações eletroquímicas com potencial tecnológico somente são viabilizadas quando realizadas sob condições que garantam uma velocidade (ou corrente elétrica) adequada, ou seja, com uso de materiais eletródicos que apresentem elevada eficiên-cia eletrocatalítica. Em sistemas operacionais, fatores associados ao transporte de massa podem também se tornar etapas importantes no processo global de transferência de carga e, assim, a extensão da área superficial desempenha um papel crucial sobre sua velocidade. Neste trabalho são discutidos os processos eletrocatalíticos que ocorrem nas células a combustível com eletrólito polimérico (PEMFC), ou seja, as reações de oxidação de hidrogênio (ROH) e ...

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A study of methanol electro-oxidation reactions in carbon membrane electrodes and structural properties of Pt alloy electro-catalysts by EXAFS

Cited by 124 publications

References 18 publications

Physical and electrochemical characterization of catalysts for oxygen reduction in fuel cells

Physical and electrochemical characterization of catalysts for oxygen reduction in fuel cells

Silicon nanograss as micro fuel cell gas diffusion layer

Eletrocatálise das reações de oxidação de hidrogênio e de redução de oxigênio

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