A survey of platinum hydrous oxide electrochemistry at elevated temperature: evidence for a new component in the ?-deposit

Burke, L.D.; Morrissey, Joanne

doi:10.1007/bf00253457

Cited by 7 publications

(9 citation statements)

References 34 publications

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“…shows SEM images of a 0.16 μg Pt cm -2 catalyst layer, on a gold coated porous polycarbonate substrate. The substrate has 400 nm diameter 55 pores, hydrophobized by the AF and a tortuosity of 1. Furthermore, the catalyst particles preferentially deposited at the pores at this catalyst loading, allowing for the optimum conditions depicted in Figure Error …”

Section: Resultsmentioning

confidence: 99%

“…As the pores are 400 nm, they have negligible constriction of the flow (δ = 1). 55 Fickian diffusion was assumed because the pore size is greater than the mean free path of hydrogen and oxygen at 126 and 74 nm (25 °C and 100 kPa), 40 respectively. This gives a Knudsen number of 0.315 and 0.185, for oxygen and hydrogen, respectively.…”

Section: Parameters Of the Substratementioning

confidence: 99%

“…6 In aqueous electrolytes such as H 2 SO 4 or HClO 4 , the concentration and diffusion coefficient of oxygen and hydrogen are very low, implying considerably lower limiting currents than expected for a PEFC. Even at the rotation rate limit of ~10K rpm, the limiting mass transport currents 55 densities are only 14 and 6 mA cm -2 Geo for the ORR and HOR, respectively. 7 PEFCs operating with pure hydrogen and oxygen can have current densities up to three orders of magnitude higher than this.…”

Section: Introductionmentioning

confidence: 96%

“…[26][27][28] More recently, the floating electrode has been adapted for PEFC studies. 29,30 Antolini et al 29 fabricated electrodes to study 55 geometry effects such as PFSA content, an important parameter of PEFC electrodes. This catalyst layer was 40 μm thick, with a loading of 200 μg Pt cm -2 ; not optimized for intrinsic catalyst property studies.…”

Section: Introductionmentioning

confidence: 99%

“…As stated above, the porous PCTE membranes used in our studies have a pore density of 10 8 pores cm -2 , which is equivalent to an average distance between pores of about 1.1 μm. A characteristic current density j cond of 0.21 A cm -2 (0.14 A cm -2 ) 55 can be calculated for ORR (HOR) using standard values for the solubilities (O 2 : 1.27 × 10 -3 mol dm -3 ; H 2 : 0.78 × 10 -3 mol dm -3 ), diffusion coefficients (O 2 : 2.42 × 10 -5 cm 2 s -1 ; H 2 : 5.11 × 10 -5 cm 2 s -1 ) in water at 25 °C 40 and r p = 565 nm. Note that this neglects salting-out effects.…”

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confidence: 99%

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Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Zalitis

Kramer

Kucernak

2013

Phys. Chem. Chem. Phys.

180

194

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An alternative approach to the rotating disk electrode (RDE) for characterising fuel cell electrocatalysts is presented. The approach combines high mass transport with a flat, uniform, and homogeneous catalyst deposition process, well suited for studying intrinsic catalyst properties at realistic operating conditions of a polymer electrolyte fuel cell (PEFC). Uniform catalyst layers were produced with loadings as low as 0.16 μg Pt cm -2 and thicknesses as low as 200 nm. Such ultra thin catalyst layers are considered 10 advantageous to minimize internal resistances and mass transport limitations. Geometric current densities as high as 5.7 A cm -2 Geo were experimentally achieved at a loading of 10.15 μgPt cm -2 for the hydrogen oxidation reaction (HOR) at room temperature, which is three orders of magnitude higher than current densities achievable with the RDE. Modelling of the associated diffusion field suggests that such high performance is enabled by fast lateral diffusion within the electrode. The electrodes operate over a wide 15 potential range with insignificant mass transport losses, allowing the study of the ORR at high overpotentials. Electrodes produced a specific current density of 31 ± 9 mA cm -2Spec at a potential of 0.65 V vs. RHE for the oxygen reduction reaction (ORR) and 600 ± 60 mA cm -2 Spec for the peak potential of the HOR. The mass activities of Pt/C catalysts towards the ORR was found to exceed a range of literature PEFC mass activities across the entire potential range. The HOR also revealed fine structure in 20 the limiting current range and an asymptotic current decay for potentials above 0.36 V. These characteristics are not visible with techniques limited by mass transport in aqueous media such as the RDE. IntroductionUnderstanding the kinetics of the oxygen reduction reaction 25 (ORR) and hydrogen oxidation reaction (HOR) on platinum nano-particles is vital for polymer electrolyte fuel cell (PEFC) development. Each platinum nano-particle within the electrode should have optimal proton access, gas access and an electronic path to study intrinsic electrocatalytic properties of the catalyst. 30 These three criteria should be maintained throughout the working conditions (e.g., temperature, humidity and potential). If a reaction site is starved for any of the three, its activity will be reduced, which skews the average activity and introduces an error. It is paramount to minimize the number of underperforming 35 catalyst sites to determine intrinsic catalyst properties. Ideally, the catalyst layer should be made as thin as possible. Thus, all the catalyst particles will be close to the perfluorosulfonic acid (PFSA) membrane for ionic access and close to the gas diffusion layer (GDL) for gas access and an electronic path, removing 40 internal limitations. Mass transport limitations lead to concentration polarization across thick electrodes, 1-3 limiting the active thickness to about 5 μm at high current densities, regardless of how thick the catalyst layer is. 1 The majority of ORR and ...

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Section: Resultsmentioning

confidence: 99%

Section: Parameters Of the Substratementioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 3 more Smart Citations

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Zalitis

Kramer

Kucernak

2013

Phys. Chem. Chem. Phys.

180

194

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The electrochemistry of gold: I the redox behaviour of the metal in aqueous media

1997

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Gold is frequently regarded as the ideal metal for the investigation of solid electrode behaviour, which in aqueous media is often considered in very simplistic terms as being that of a metal which is highly resistant to dissolution. Gold possesses very weak chemisorbing properties and an extensive double layer region that in the presence of most pure electrolytes is often assumed to be totally free of Faradaic behaviour, and exhibits a monolayer (or AUZ03) oxide formation/removal reaction at quite positive potentials. However, recent investigations have revealed that the electrochemistry of polycrystalline gold in aqueous solution is considerably more complex. Two significantly different types of oxide deposits, monolayer (or a) and hydrous (or~), may be produced on the metal and the behaviour of the~-deposit is quite unusual. It is suggested that not only the behaviour of the~-oxide but, far more important from a practical viewpoint, the catalytic and electrocatalytic behaviour of gold (which will be discussed in more detail in Part II)' may be rationalized in terms of the active state (or states) of gold. This active state (frequently present only at very low coverage) reacts in a manner that is quite different from that of stable gold. The nature of the active state of gold deserves far more attention than it has received to date.The importance of surface reactions was highlighted in a recent article by Sachtler (l) who pointed our that ca 17% of GNP in the US and ca 25% in the case of Germany are derived from materials produced by catalytic processes. Most of these processes involve heterogeneous catalysis of gas phase reactions on metal or oxide surfaces. The catalysis of electrode reactions is also important, eg ca 13 million tons (valued at ca 2.2 billion dollars) of chlorine gas (2) is produced annually in the US, largely with the aid of electro catalytically active dimensionally stable (Ru02/Ti02)/Ti) anodes.The potential in the electro catalysis field is also quite significant; for example, the development of effective electrocatalysts for the direct methanol/air fuel cell would revolutionise the transport industry. Compared with the internal combustion engine, widely used at present, fuel cells in general offer the prospect of more efficient, cleaner and less noisy energy conversion. Methanol is a much more easily stored fuel than hydrogen for use in mobile energy conversion systems and may, with the development of CS:9' GoldBulletin 1997, 30(2) more efficient methanol oxidation electrocatalysts, be the system of choice for operation at ambient, or slightly elevated, temperatures in vehicles.

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Improvement of the electrocatalytic activity of platinum in oxidation of aromatic compounds

Samet

Mefteh

Abdelhédi

et al. 2008

Comptes Rendus. Chimie

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The electrochemical oxidation of aromatic compounds (ACs) at pre-treated platinum electrodes was studied by cyclic voltammetry (CV). An understanding of the mechanism of the different electrochemical processes is possible only if taking into account the state of the Pt electrode surface, which is strongly affected by oxide formation and reduction. Long-time treatment by CV yields increased Pt oxide coverage and leads to very important electrocatalytic properties towards many organic electro-oxidation reactions. Three aromatic compounds were studied: phenol, hydroquinone and p-benzoquinone. The results show that the increase of the charge Q which characterizes the surface quality of the pre-treated Pt electrodes entails an increase in active sites with respect to the discharge of water to form PtOH species which typically starts at ca. 0.12 V. Once such species are formed they react with both free and adsorbed molecules. It results in the multiplication of the oxidation current by factors of 46 and 21 for phenol and pbenzoquinone, respectively, when Q increases from 0.3 to 4 mC. In the case of hydroquinone this factor is only about 3 for the same increase of Q. The oxidation of hydroquinone is not catalyzed by the PtOH species because it takes place at potential lower than 0.12 V. The results show that phenol is quantitatively oxidized by CV on a pre-treated platinum electrode to produce by the intermediary of catechol, hydroquinone, p-benzoquinone, oxalic and maleic acids, whose degradation leads to carbon dioxide.

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A survey of platinum hydrous oxide electrochemistry at elevated temperature: evidence for a new component in the ?-deposit

Cited by 7 publications

References 34 publications

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

The electrochemistry of gold: I the redox behaviour of the metal in aqueous media

Improvement of the electrocatalytic activity of platinum in oxidation of aromatic compounds

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