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- Seidel, Y.E., et al.
(författare)
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Mesoscopic mass transport effects in electrocatalytic processes
- 2008
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 140, s. 167-184
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Tidskriftsartikel (refereegranskat)abstract
- The role of mesoscopic mass transport and re-adsorption effects in electrocatalytic reactions was investigated using the oxygen reduction reaction (ORR) as an example. The electrochemical measurements were performed on structurally well-defined nanostructured model electrodes under controlled transport conditions in a thin-layer flow cell. The electrodes consist of arrays of Pt ultra-microelectrodes (nanodisks) of defined size (diameter similar to 100 nm) separated on a planar glassy carbon (GC) substrate, which were fabricated employing hole-mask colloidal lithography (HCL). The measurements reveal a distinct variation in the ORR selectivity with Pt nanodisk density and with increasing electrolyte flow, showing a pronounced increase of the H2O2 yield, by up to 65%, when increasing the flow rate from 1 to 30 mu L s(-1). These results are compared with previous findings and discussed in terms of a reaction model proposed recently (A. Schneider et al., Phys. Chem. Chem. Phys., 2008, 10, 1931), which includes (i) direct reduction to H2O on the Pt surface and (ii) additional H2O2 formation and desorption on both Pt and carbon surfaces and subsequent partial re-adsorption and further reduction of the H2O2 molecules on the Pt surface. The potential of model studies on structurally defined catalyst surfaces and under well-defined mass transport conditions in combination with simulations for the description of electrocatalytic reactions is discussed.
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- Seidel, Y.E., et al.
(författare)
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Mesoscopic transport effects in electrocatalytic reactions
- 2009
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781566777902 ; 25:23, s. 91-102
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Konferensbidrag (refereegranskat)abstract
- Transport effects may not only influence the rate of electrocatalytic reactions, but also the product distribution. The underlying effects were studied under well-defined reaction and transport conditions, using nanostructured Pt/glassy carbon electrodes, which consist of ordered arrays of electrocatalytically active Pt nanostructures on a planar glassy carbon substrate. The effect of varying the density of the Pt nanostructures or the electrolyte flow rate on the reaction characteristics and product distribution was investigated for apparently simple electrocatalytic reactions such as CO oxidation, methanol oxidation and oxygen reduction. It is shown that reducing the Pt coverage leads to an increase of the relative amount of the reaction intermediates. Similar effects are obtained for increasing the electrolyte flow rate. The results are discussed on a molecular scale in terms of the 'desorption - re-adsorption - reaction' model which we had introduced recently.
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- Seidel, Y. E., et al.
(författare)
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Nanostructured Pt/GC model electrodes prepared by the deposition of metal-salt-loaded micelles
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:10, s. 5795-5801
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Tidskriftsartikel (refereegranskat)abstract
- Novel, nanostructured, carbon-supported Pt model electrodes with homogeneously distributed Pt nanoparticles of uniform size were fabricated and analyzed with respect to their electrochemical properties. For this purpose, Pt-salt-loaded micelles were deposited on a glassy carbon substrate and subsequently exposed to an oxygen plasma and a H-2 atmosphere for removal of the polymer carriers and reduction of the Pt salt. The morphology of the resulting nanoparticles and their electrochemical/electrocatalytic properties were characterized by high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential electrochemical mass spectrometry for CO electrooxidation. The data demonstrate that this method is generally suited to the production of nanostructured model electrodes with well-defined and independently adjustable particle size and interparticle distance distributions, which are specifically suited for quantitative studies of transport processes in electrocatalytic reactions.
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- Seidel, Y.E., et al.
(författare)
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Oscillatory behaviour in Galvanostatic Formaldehyde Oxidation on Nanostructured Pt/Glassy Carbon Model Electrodes
- 2010
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 11:7, s. 1405-1415
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Tidskriftsartikel (refereegranskat)abstract
- The electrocatalytic oxidation of formaldehyde, which results in CO, and HCOOH formation, was investigated under galvanostatic conditions on nanostructured Pt/glassy carbon (GC) electrodes fabricated by employing colloidal lithography (CL). The measurements were performed on structurally well-defined model electrodes of different Pt surface coverages under different applied currents (current densities) and at constant electrolyte transport in a thin-layer flow cell connected to a differential electrochemical mass spectrometry (DEMS) setup to monitor the dynamic response of the reaction selectivity under these conditions. Periodic oscillations of the electrode potential and the CO, formation rate appear not only for a continuous Pt film, but also for the nanostructured Pt/GC electrodes when a critical current density is exceeded. The critical current density for achieving regular osillation patterns increased with decreasing Pt nanodisk density. Lower oscillation frequencies of the electrode potential and lower CO2 formation rate for nanostructured Pt/GC electrodes compared to continuous Pt film at similar applied current densities suggest that transport processes play an essential role. Moreover, from the simple periodic response of the nanostructured electrodes it follows that all individual Pt disks in the array oscillate in synchrony. This result is discussed in terms of the different modes of spatial coupling present in the system: global coupling, migration coupling and mass transport of the essential chemical species, and the coverage of corresponding adsorbates.
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