Oxygen reduction on stepped platinum surfaces in acidic media

Kuzume, Akiyoshi; Herrero, Enrique; Feliu, Juan M.

doi:10.1016/j.jelechem.2006.05.006

Cited by 354 publications

(407 citation statements)

References 28 publications

(100 reference statements)

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“…Feliu and co-workers 39,40 intensively studied the effect of surface orientation of single Pt crystals on ORR electron transfer, and concluded that the ORR is actually a structuresensitive reaction in both sulfuric and perchloric media. The orientation of the steps and terraces on the surface plays a significant role in determining the electrocatalytic activity of an electrode.…”

Section: Current Status-geometric and Compositional Strategiesmentioning

confidence: 99%

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

et al. 2010

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In this critical review, we present the current technological advances in proton exchange membrane (PEM) fuel cell catalysis, with a focus on strategies for developing nanostructured Pt-alloys as electrocatalysts for the oxygen reduction reaction (ORR). The achievements are reviewed and the major challenges, including high cost, insufficient activity and low stability, are addressed and discussed. The nanostructured Pt-alloy catalysts can be grouped into different clusters: (i) Pt-alloy nanoparticles, (ii) Pt-alloy nanotextures such as Pt-skins/monolayers on top of base metals, and (iii) branched or anisotropic elongated Pt or Pt-alloy nanostructures. Although some Pt-alloy catalysts with advanced nanostructures have shown remarkable activity levels, the dissolution of metals, including Pt and alloyed base metals, in a fuel cell operating environment could cause catalyst degradation, and still remains an issue. Another concern may be low retention of the nanostructure of the active catalyst during fuel cell operation. To facilitate further efforts in new catalyst development, several research directions are also proposed in this paper (130 references).

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Section: Current Status-geometric and Compositional Strategiesmentioning

confidence: 99%

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

et al. 2010

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“…Importantly, research on atomically well-defined single-crystal electrodes has revealed a strong crystallographic orientation dependence of the ORR activity. 9,14,17,18 The catalytic activity of the ORR on the three basal planes of Pt 50 has been investigated widely in different electrolytes. [19][20][21][22][23] In sulfuric acid, the reactivity of the Pt basal planes decreases in the order (110) > (100) > (111), 20 following the relative adsorption strength of the sulfate anion.…”

Section: Introductionmentioning

confidence: 99%

“…24 Similar relative reactivity patterns have been found in non-specific adsorbing perchlorate electrolyte, although the 60 variation in activities is much smaller. 17,18 While single-crystal electrodes provide valuable information on systematic trends, the availability of surfaces can be limited, with high-index surfaces particularly challenging to prepare and maintain. Furthermore, the activity of grain boundaries, which are present in real catalysts and on polycrystalline electrodes, cannot 5 be studied on single-crystal surfaces, even though these features have been suggested to play a large role in real catalysts.…”

Section: Introductionmentioning

confidence: 99%

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

Chen

Meadows

Cuharuc

et al. 2014

Phys. Chem. Chem. Phys.

111

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The scanning droplet-based technique, scanning electrochemical cell microscopy (SECCM), combined with electron backscatter diffraction (EBSD), is demonstrated as a powerful approach for visualizing surface structure effects on the rate of the oxygen reduction reaction (ORR) at polycrystalline platinum electrodes. Elucidating the effect of electrode structure on the ORR is of major interest in connection to 10 electrocatalysis for energy-related applications. The attributes of the approach herein stem from: (i) the ease with which the polycrystalline substrate electrode can be prepared; (ii) the wide range of surface character open to study; (iii) the possibility of mapping reactivity within a particular facet (or grain), in a pseudo-single crystal approach, and acquiring a high volume of data as a consequence; (iv) the ready ability to measure the activity at grain boundaries; and (v) an experimental arrangement (SECCM) that 15 mimics the three-phase boundary in low temperature fuel cells. The kinetics of the ORR was analyzed and a finite element model was developed to explore the effect of the three-phase boundary, in particular to examine pH variations in the droplet and the differential transport rates of the reactants and products. We have found a significant variation of activity across the platinum substrate, inherently linked to the crystallographic orientation, but do not detect any enhanced activity at grain boundaries. Grains with 20 (111) and (100) contributions exhibit considerably higher activity than those with (110) and (100) contributions. These results, which can be explained by reference to previous single crystal measurements, enhance our understanding of ORR structure-activity relationships on complex high-index platinum surfaces, and further demonstrate the power of high resolution flux imaging techniques to visualize and understand complex electrocatalyst materials.

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“…3,4 In mechanistic studies the two pathways are discussed in terms of the formation of OOH on the surface (associative mechanism) or of the adsorption of atomic oxygen (dissociative mechanism) 5,6 but the nature of the intermediates is still unclear; while most invoke adsorbed OH species, 7 recent studies support the existence of a soluble intermediate. 3,8,9 The complexity of the reaction is reflected by the dependence of the apparent number of electrons, n app , on experimental conditions including electrode material, 10 surface crystal planes, 11 pH, 12 and even mass transport conditions. [13][14][15] Except for a few studies, 11,[16][17][18][19][20][21] the reaction has been mostly investigated under steady state mass transport conditions with rotating disc, rotating ring-disc, hanging meniscus rotating disc and microelectrodes.…”

Section: A Introductionmentioning

confidence: 99%

Transient study of the oxygen reduction reaction on reduced Pt and Pt alloys microelectrodes: evidence for the reduction of pre-adsorbed oxygen species linked to dissolved oxygen

Perry

Denuault

2015

Phys. Chem. Chem. Phys.

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Using chronoamperometry at preconditioned oxide-free Pt microdisc electrodes in aqueous media, we investigated the oxygen reduction reaction (ORR) on the millisecond timescale and obtained results consistent with the reduction of oxygen species which adsorb on the electrode before the ORR is electrochemically driven. Furthermore these adsorbed species are clearly linked to oxygen in solution. At long times, the amperometric response is solely controlled by the diffusion of dissolved oxygen towards the microelectrode. However, at short times, typically below 50 ms, the reduction of pre-adsorbed oxygen produces a large extra current whose magnitude depends on the oxygen concentration in solution, deliberate electrode poisoning and the rest time before the potential step. Using sampled current voltammetry we show that this extra current affects the entire potential range of the ORR. Using microdisc electrodes made with Pt alloys we find that the amperometric response is sufficiently sensitive to distinguish oxygen coverage differences between Pt, Pt0.9Rh0.1 and Pt0.9Ir0.1 microdiscs. These unexpected and, to our knowledge, never previously reported results provide new insight into the oxygen reduction reaction on Pt. The existence over a wide potential range of irreversibly adsorbed oxygen species arising from dissolved oxygen and different from Pt oxide is particularly relevant to the development of oxygen reduction catalysts for low temperature fuel cells. A. IntroductionThe electroreduction of oxygen in aqueous media is a complex reaction which involves the cleavage of the oxygen bond, adsorption and desorption of intermediates and the transfer of four electrons and four protons. While the overall mechanism is commonly discussed in terms of a series two 2-electron peroxide pathway running in parallel with a direct 4-electron process, 1, 2 the elementary steps and, crucially, the nature of the rate determining step remain uncertain. 3,4 In mechanistic studies the two pathways are discussed in terms of the formation of OOH on the surface (associative mechanism) or of the adsorption of atomic oxygen (dissociative mechanism) 5,6 but the nature of the intermediates is still unclear; while most invoke adsorbed OH species, 7 recent studies support the existence of a soluble intermediate. 3,8,9 The complexity of the reaction is reflected by the dependence of the apparent number of electrons, n app , on experimental conditions including electrode material, 10 surface crystal planes, 11 pH, 12 and even mass transport conditions. [13][14][15] Except for a few studies, 11, 16-21 the reaction has been mostly investigated under steady state mass transport conditions with rotating disc, rotating ring-disc, hanging meniscus rotating disc and microelectrodes.Here we report the unexpected, and to our knowledge never previously reported, results obtained when studying the ORR under transient conditions on the millisecond timescale. To acquire data undistorted by the charging and discharging of the double layer we employ micro...

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Oxygen reduction on stepped platinum surfaces in acidic media

Cited by 354 publications

References 28 publications

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

Transient study of the oxygen reduction reaction on reduced Pt and Pt alloys microelectrodes: evidence for the reduction of pre-adsorbed oxygen species linked to dissolved oxygen

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