The role of surface oxygenated-species and adsorbed hydrogen in the oxygen reduction reaction (ORR) mechanism and product selectivity on Pd-based catalysts in acid media

Rahul, Ramesh; Singh, Ramesh Kumar; Bera, Bapi; Devivaraprasad, Ruttala; Neergat, Manoj

doi:10.1039/c5cp00692a

Cited by 66 publications

(53 citation statements)

References 67 publications

(210 reference statements)

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“…Testing of carbon-supported palladium oxide-based catalysts has shown that PdO itself is rather inactive towards the ORR in perchloric acid, but the activity increases when the oxides are reduced [28]. In addition, on oxide covered Pd electrode the peroxide yield is higher than on oxide-free surface as a result of active site blocking by the oxides.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Recent progress in oxygen reduction electrocatalysis on Pd-based catalysts

Erikson

Sarapuu

Solla-Gullón

et al. 2016

Journal of Electroanalytical Chemistry

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Palladium-based catalysts for electrochemical reduction of oxygen have received increasing attention as potential replacement for platinum-based materials in the fuel cells. This Review summarises the research conducted with nanostructured palladium catalysts, including thin nanostructured films and Pd nanoparticles on various carbon and non-carbon supports. The mechanism of oxygen reduction on palladium is described and the effect of the particle size and shape on the electrocatalytic activity is emphasised. The role of the support material and additives on the oxygen reduction activity of Pd nanoparticles is also discussed. The electrocatalytic activity of Pd-based catalysts is evaluated in terms of specific activity and mass activity. The application of supported Pd nanoparticles as cathode catalysts for lowtemperature fuel cells is highlighted. Some insights into the remaining challenges and directions for further development of Pd-based oxygen reduction electrocatalysts are provided.

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Section: Accepted Manuscriptmentioning

confidence: 99%

Recent progress in oxygen reduction electrocatalysis on Pd-based catalysts

Erikson

Sarapuu

Solla-Gullón

et al. 2016

Journal of Electroanalytical Chemistry

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“…In previous studies, Inaba et al 47 and Schneider et al 48 reported that a decrease of the number of active sites in Pt/C catalysts yielded a similar transition from an (apparent) four-electron ORR toward a two-electron reduction. 47 The same phenomenon seems to hold in the case of Pd/C catalysts (cf., Rahul et al 49 brought up this hypothesis when comparing the ORR on nanoparticulate Pd, Pd 3 Co and Pt at identical metal loadings, but at different site densities, due to different metal densities), except that owing to their lower ECSA stability, this transition toward a two-electron ORR is observed earlier, namely at already ≈500 cycles for 20% Pd/C (fast ECSA loss due to smallest initial particle size) and at ≈2500 cycles for 40% Pd/C (slower ECSA loss due to larger initial particle size). If we hypothesize that the intrinsic nature of the ORR remains unchanged by either the variation of catalyst loading 47 or by the voltage cycling induced particle growth and ECSA loss, and that only one of the intermediate steps during the ORR can be promoted or hindered to lead to the observed reaction mechanism, the general ORR pathways sketched in Figure 8 would suggest two possibilities for an apparent four-electron ORR when the direct four-electron reduction (pathway i) is not predominant.…”

mentioning

confidence: 99%

Monometallic Palladium for Oxygen Reduction in PEM Fuel Cells: Particle-Size Effect, Reaction Mechanism, and Voltage Cycling Stability

Mittermeier

Weiß

Gasteiger

et al. 2017

J. Electrochem. Soc.

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In this experimental study, we determine the size dependent activity as well as accelerated voltage cycling stability of various carbon supported palladium electrocatalysts for the oxygen reduction in acidic medium. Furthermore, ex-situ transmission electron microscopy studies before and after accelerated voltage cycling provide a deeper understanding regarding particle stability during voltage cycling. Regarding oxygen reduction, a particle size effect on the specific activity is observed, with bulky Pd-black (≈4 m 2 g −1 Pd ) exhibiting ≈x6 times higher activity than Pd supported on Vulcan carbon (≈190 m 2 g −1 Pd ). Mass activities, however, exhibit a strong correlation with catalyst surface area at small electrochemically active surface area (ECSA) values, but are observed to be nearly constant between ≈50−200 m 2 g −1 Pd . As stability tests during voltage cycling reveal a benefit for smaller surface areas, i.e. bigger particles, a limited gain in stability can be achieved by increasing catalyst particle size at a negligible cost of electrocatalytic mass-based activity. Moreover, we provide a deeper insight regarding the oxygen reduction reaction mechanism and show significant hints that a sequential two-plus-two electron reduction mechanism via intermediate hydrogen peroxide is likely to occur on carbon supported Pd catalysts.

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“…on ORR and organic molecule oxidation reactions with platinum single crystal electrodes are well documented in the literature. [10][11][12][13][14][15][16][17][18][19][20][21] Feliu et al, Abruna et al, and others have extensively investigated the influence of halides (I − , Br − , Cl − ) on platinum single crystal electrodes. [22][23][24][25][26][27][28][29][30][31][32][33][34][35] Most of the available surface sensitive techniques were used to elucidate adsorbate coverage and structure.…”

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confidence: 99%

Recovery of Active Surface Sites of Shape-Controlled Platinum Nanoparticles Contaminated with Halide Ions and Its Effect on Surface-Structure

Devivaraprasad¹,

Kar²,

Leuaa³

et al. 2017

J. Electrochem. Soc.

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The interaction of halide ions (I − , Br − , Cl − ) with well-cleaned faceted platinum (nanocube, cuboctahedral) nanoparticles and platinum polycrystalline is investigated in 0.5 M H 2 SO 4 electrolyte. Under electrochemical conditions, the Pt surface gets poisoned with halide ad-atoms and it causes the attenuation of both hydrogen adsorption/desorption in the lower potential region (0.06-0.4 V) and electroxidation of Pt nanoparticles in the higher potential region (0.6-1.2 V). Above certain concentration (5 × 10 −6 M), the strongly adsorbing I − ions mask the H upd features. On the other hand, Br − and Cl − ions alter the peak features in the H upd region, those are characteristic of different Pt surface sites. On excursion to higher potentials (∼>1.2 V), concurrent halogen evolution, Pt oxidation, and oxygen evolution are observed; the increase in peak intensity in the H upd region reflects the reconstruction of the Pt surface. To remove the adsorbed halide ions from the Pt surface, an in-situ potentiostatic method is employed, which involves holding the working electrode at ∼0.03 V in 0.1 M NaOH solution. The cleanliness and retention of surface-structure are confirmed from the voltammograms recorded in the test electrolyte and the recovery of oxygen reduction reaction (ORR) activity after cleaning the Br − ion-contaminated Pt surface supports this conjecture. Anions specifically adsorbed on precious metal surfaces adversely impact several electrochemical reactions including oxidation/ reduction, metal deposition, corrosion and dissolution.1-6 Catalyst poisoning by the adsorbed anions (halides, sulfates and others) is a well-known phenomenon and it decreases the activity of electrocatalysts; for example, in fuel-cell, batteries and electrolyzers. 7,8 Especially platinum, a material for catalyzing a variety of electrochemical reactions, is prone to get poisoned in the presence of adatoms/adsorbates/solution anions under electrochemical conditions. Thus, oxygen reduction reaction (ORR) in fuel cells is affected by the adsorbed species or impurities and it is highly dependent on the cleanliness and surface structure of the catalyst. [9][10][11][12][13] In hydrogen-bromine fuel cells, bromides and bromine species migrate across the membrane and poison the hydrogen-electrode catalyst; moreover, Pt dissolves in Br − ion-containing solutions. 22-35 Most of the available surface sensitive techniques were used to elucidate adsorbate coverage and structure. Such techniques, including auger electron spectroscopy (AES), low energy electron diffraction (LEED), second harmonic generation (SHG), surface X-ray scattering (SXS), electrochemical scanning tunneling microscope (ESTM) 31,34 and electrochemical quartz crystal microbalance (EQCM), used to investigate anion adsorption have offered significant insight on the dependence of adsorption process on exposed single crystal orientations. Thus, AES/LEED studies revealed that Cl − ion adsorption occurs on Pt(100) surface at lower potential than that with Pt(111) surfaces, indi...

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The role of surface oxygenated-species and adsorbed hydrogen in the oxygen reduction reaction (ORR) mechanism and product selectivity on Pd-based catalysts in acid media

Cited by 66 publications

References 67 publications

Recent progress in oxygen reduction electrocatalysis on Pd-based catalysts

Recent progress in oxygen reduction electrocatalysis on Pd-based catalysts

Monometallic Palladium for Oxygen Reduction in PEM Fuel Cells: Particle-Size Effect, Reaction Mechanism, and Voltage Cycling Stability

Recovery of Active Surface Sites of Shape-Controlled Platinum Nanoparticles Contaminated with Halide Ions and Its Effect on Surface-Structure

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