A. Wieckowski

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (238)405.87 Total impact

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    ABSTRACT: Surface vibrational spectroscopy techniques probe the structure and composition of interfaces at the molecular level. Their versatility, coupled with their non-destructive nature, enables in-situ measurements of operating devices and the monitoring of interface-controlled processes under reactive conditions. Vibrational Spectroscopy at Electrified Interfaces explores new and emerging applications of Raman, infrared, and non-linear optical spectroscopy for the study of charged interfaces. The book draws from hundreds of findings reported in the literature over the past decade. It features an internationally respected team of authors and editors, all experts in the field of vibrational spectroscopy at surfaces and interfaces. Content is divided into three parts: Part One, Nonlinear Vibrational Spectroscopy, explores properties of interfacial water, ions, and biomolecules at charged dielectric, metal oxide, and electronically conductive metal catalyst surfaces. In addition to offering plenty of practical examples, the chapters present the latest measurement and instrumental techniques. Part Two, Raman Spectroscopy, sets forth highly sensitive approaches for the detection of biomolecules at solid-liquid interfaces as well as the use of photon depolarization strategies to elucidate molecular orientation at surfaces. Part Three, IRRAS Spectroscopy (including PM-IRRAS), reports on wide-ranging systems—from small fuel molecules at well-defined surfaces to macromolecular complexes—that serve as the building blocks for functional interfaces in devices designed for chemical sensing and electric power generation.
    edited by Andrzej Wieckowski, Carol Korzeniewski and Björn Braunschweig, 10/2013; John Wiley & Sons., ISBN: 978-1-118-15717-6
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    ABSTRACT: In this report, we discuss some of the advances in surface science and theory that have enabled a more detailed understanding of the mechanisms that govern the electrocatalysis. More specifically, we examine in detail the electrooxidation of C-1 and C-2 alcohol molecules in both acidic and basic media. A combination of detailed in situ spectroscopic measurements along with density functional theory calculations have helped to establish the mechanisms that control the reaction paths and the influence of acidic and alkaline media. We discuss some of the synergies and differences between electrocatalysis and aqueous phase heterogeneous catalysis. Such analyses begin to establish a common language and framework by which to compare as well as advance both fields. (C) 2012 Elsevier B.V. All rights reserved.
    Catalysis Today 01/2013; · 3.31 Impact Factor
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    ABSTRACT: Quantitative monitoring of water conditions in a field is a critical ability for environmental science studies. We report the design, fabrication and testing of a low cost, miniaturized and sensitive electrochemical based nitrate sensor for quantitative determination of nitrate concentrations in water samples. We have presented detailed analysis for the nitrate detection results using the miniaturized sensor. We have also demonstrated the integration of the sensor to a wireless network and carried out field water testing using the sensor. We envision that the field implementation of the wireless water sensor network will enable "smart farming" and "smart environmental monitoring".
    Journal of Environmental Monitoring 11/2012; · 2.09 Impact Factor
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    ABSTRACT: The design of polymer electrolyte fuel cell electrocatalysts depends on two equally important fundamental principles: the optimization of electrocatalytic activities as well as the long-term stability under operating conditions (e.g., pH < 1 and E > 0.8 V). Pt-based alloys with transition metals (i.e., Pt–La) address both of these key issues. The oxygen reduction kinetics depends on the alloy composition which, in turn, is related to the d-band center position. The stability of the oxygen reduction reaction is predictable by correlation of the d-band fillings and vacancies of Pt–M (M = Ti, Fe, Zr and La).
    Energy & Environmental Science 05/2012; 5(6):7521-7525. · 11.65 Impact Factor
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    ABSTRACT: Ethanol electrooxidation reaction (EOR) pathways on polycrystalline platinum were studied with broadband sum-frequency generation (BB-SFG) spectroscopy and electrochemistry in unprecedented detail and under working fuel cell conditions. We present the first observation of adsorbed acetate and co-adsorbed sulfuric acid anions with SFG and a discussion of their relation to the EOR. Surface-adsorbed intermediates such as CO on Pt atop sites and acetate are observed in both H2SO4 and HClO4 solutions. However, CO molecules on bridge sites and sulfuric acid anions are found in H2SO4 only. At E < 0.5 V vs. Ag/AgCl, CO is the predominantly adsorbed species. Increasing the potential to E > 0.5 V results in the oxidative removal of CO and the adsorption of acetate anions. Experiments with isotopically labeled ethanol (12CH313CH2OH) reveal information on the carbon–carbon bond cleavage and the subsequent CO formation. In particular, the methyl fragment (–12CHx) produces far less 12CO and suggests methyl electroreduction to methane and/or the persistence of –CHx on the Pt surface.Graphical abstractPotentiodynamic broadband sum-frequency generation and electrochemistry were used to elucidate the mechanism of ethanol electrooxidation on polycrystalline platinum in acidic electrolytes.View high quality image (50K)Research highlights► Electrocatalysis of ethanol on polycrystalline Pt surfaces. ► Reaction pathways revealed by sum-frequency generation (SFG) and electrochemistry. ► Surfaces-adsorbed intermediates include CO, acetate, and methyl fragment of ethanol produces –CHx. ► –CHx is difficult to oxidize. ► Electrolyte anions affect adsorption of intermediates CO and acetate.
    Journal of Catalysis 01/2011; 278(2):181-188. · 5.79 Impact Factor
  • A. Wieckowski, M. Neurock
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    ABSTRACT: The advances in spectroscopy and theory that have occurred over the past two decades begin to provide detailed in situ resolution of the molecular transformations that occur at both gas/metal as well as aqueous/metal interfaces. These advances begin to allow for a more direct comparison of heterogeneous catalysis and electrocatalysis. Such comparisons become important, as many of the current energy conversion strategies involve catalytic and electrocatalytic processes that occur at fluid/solid interfaces and display very similar characteristics. Herein, we compare and contrast a few different catalytic and electrocatalytic systems to elucidate the principles that cross-cut both areas and establish characteristic differences between the two with the hope of advancing both areas.
    Advances in Physical Chemistry 01/2011; 2011.
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    ABSTRACT: Cited By (since 1996):12, Export Date: 5 November 2013, Source: Scopus
    Journal of Physical Chemistry Letters 01/2011; 2(17):2236-2240. · 6.59 Impact Factor
  • Stephanie N. S. Goubert-Renaudin, Andrzej Wieckowski
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    ABSTRACT: Unsuccessful attempts in using Ni and/or Co nanoparticles as catalysts for oxygen reduction reaction (ORR) are reported. Several synthetic approaches such as encapsulation of nanoparticles in dendrimers, coating by polyethylene glycol and surface modification by anthraquinone were carried out to isolate the nanoparticles from aqueous corrosive media and to prevent their agglomeration at very low and very high pH. In all the attempts described, negative results towards ORR were consistently obtained. On the contrary, in the case of cobalt incorporated in a polypyrrole matrix (Co–Ppy–C) a catalytic activity for oxygen reduction both in acidic and alkaline medium was observed. The data indicate that neither Ni nor Co surface sites, when not coordinated to the matrix nitrogen, are electroactive towards oxygen reduction, pointing out the crucial role of the heteroatom associated with (coordinating) transition metals in the ORR catalytic process. We believe that our data are in agreement with literature although the reported data scarcity does not make the full conclusion possible. All results were obtained at room temperature, the catalytic activity of the synthesized materials at elevated temperatures are unknown.
    Journal of Electroanalytical Chemistry - J ELECTROANAL CHEM. 01/2011; 652(1):44-51.
  • P. Waszczuk, A. Crown, S. Mitrovski, A. Wieckowski
    12/2010; , ISBN: 9780470974001
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    ABSTRACT: The reversible adsorption of acetate on polycrystalline Au and Pt surfaces was investigated with broadband sum-frequency generation (SFG) and cyclic voltammetry. Specifically adsorbed acetate as well as coadsorbed sulfuric acid anions are observed for the first time with SFG and give rise to dramatically different SFG intensities on Au and Pt surfaces. While similar coverages of acetate adlayers on Au and Pt surfaces are well established by previous studies, an identification of the interfacial molecular structure has been elusive. However, we have applied the high sensitivity of SFG for interfacial polar ordering to identify different acetate structures at Au and Pt surfaces in contact with HClO(4) and H(2)SO(4) electrolytes. Acetate competes with the formation of surface oxides and shifts the oxidation threshold of both Au and Pt electrodes anodically. Effects of the supporting electrolyte on the formation of acetate adlayers are revealed by comparing SFG spectra in HClO(4) and H(2)SO(4) solutions: Sulfuric acid anions modify the potential-dependent acetate adsorption, compete with adsorbed acetate on Au and coadsorb with acetate on Pt surfaces.
    The Journal of Chemical Physics 12/2010; 133(23):234702. · 3.12 Impact Factor
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    ABSTRACT: Broad-band sum frequency generation spectroscopy (BB-SFG) was used to obtain vibrational spectra of CO adsorbates produced from formic acid oxidation on a Pt (1 0 0) electrode in sulfuric acid media. The BB-SFG simultaneously monitored all forms of the CO intermediates, including steady-state, as the potential was scanned at 5 mV/s. Spectra were compared to those obtained from CO adsorbed from a CO-saturated electrolyte. While adsorbed from HCOOH, the CO had a sharp atop transition near 2050 cm−1 and a broader multiply-bonded transitions in the 1700–1900 cm−1 range, which appear to result from bridge-like and higher-coordinated (possibly fourfold) CO. As the potential scanned from −0.2 to 0.3 V (vs. Ag/AgCl), the bridge-like CO disappeared, and the amount of atop CO increased. At potentials above 0.5 V, the CO was in steady-state, being oxidized on the surface to CO2 and replenished by CO from HCOOH. These measurements show that BB-SFG can observe potential-dependent interconversion of different CO forms on the electrode surface and can measure steady-state reaction intermediates on a surface in real time.
    Journal of Electroanalytical Chemistry. 11/2010;
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    ABSTRACT: Unpyrolyzed, non noble metal catalysts for Oxygen Reduction Reaction (ORR), denoted MeOx–CoP/C, were obtained using a two-step procedure. The procedure consisted of a synthesis of carbon-supported transition metal (Me═Co, or Ni, or Fe) nanoparticles, followed by adsorption of cobalt porphyrin (CoP). TEM and XPS analyses confirm the formation of nanoparticles and the presence of transition metal oxides. Rotating disk electrode measurements showed that the as-synthesized materials exhibit catalytic ORR activity in acidic medium toward oxygen reduction, which is higher than that of cobalt porphyrin on carbon. This reveals that the metal oxide nanoparticles enhance the activity of the metalloporphyrin without being electroactive themselves. The catalytic activity follows the sequence: CoOx–CoP/C > NiOx–CoP/C > FeOx–CoP/C, showing the influence of nature of the transition metal on the enhancing effect. The presence of a cobalt center incorporated in the macrocycle was found to be essential to the oxygen reduction reaction, appearing thus to be the catalytic active site of the reaction. Our data suggest the ORR occurs at a single active site.
    Electrochemistry Communications 11/2010; 12(11):1457–1461. · 4.29 Impact Factor
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    ABSTRACT: We present the first broadband sum-frequency generation (SFG) spectra of adlayers from sulfuric acid solutions on Pt(111) surfaces and reveal surface transformations of (bi)sulfate anions in unprecedented detail. SFG amplitudes, bandwidth, and electrochemical Stark tuning of (bi)sulfate vibrational bands centered at 1250-1290 cm(-1) strongly depend on the applied potential and are correlated with prominent voltammetric features. (Bi)sulfate adlayers on Pt(111) are important model systems for weak, specific adsorption of anions on catalytically active surfaces. Although the existence of surface transformations on Pt(111) in dilute H(2)SO(4) solutions has been established by previous studies, so far they have not been observed with surface vibrational spectroscopy. Our results confirm previous reports of a surface transformation at 0.21 V and provide new information on a second transformation at 0.5 V due to surface hydroxyl formation and rearrangement of the electric double layer.
    Journal of the American Chemical Society 10/2010; 132(40):14036-8. · 10.68 Impact Factor
  • Svetlana Strbac, Andrzej Wieckowski
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    ABSTRACT: Platinum single crystals decorated with noble metal nanoislands have found increasing applications as model systems for highly active fuel cell catalysis due to their enhanced electrocatalytic properties. Pt single crystals modified with Ru nanoislands were particularly explored due to the high catalytic efficiency of PtRu bimetallic electrodes with respect to the removal of CO poisoning during methanol oxidation. The precise geometry of the Ru-modified Pt single crystals, acquired by the use of both ex situ and in situ scanning tunneling microscopy (STM) techniques, enabled fundamental investigations of their activity from the structural perspective. Comprehensive in situ STM studies of Au single crystals decorated with Ru nanoislands were also undertaken in order to elucidate the catalytic behavior of ruthenium nanoislands, since the Au substrate alone was much less active towards CO adsorption or oxidation.
    07/2010: pages 71-116;
  • Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2010; 157(6).
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    ABSTRACT: Analysis of the surface is paramount to understanding the reactivity, selectivity, and catalytic ability of substances. In particular, this understanding is required to make an efficient use of the catalytic surfaces in fuel cells. X-ray photoelectron spectroscopy (XPS) allows determination of changes in the electronic structure for different surface preparation and composition based, mainly, on shifts of the binding energies of core-level electrons. It is also an ideal method that allows identification of the surface or near surface species in relation to fuel cell catalysis. However, the fundamental theoretical concepts, which are used to analyze and interpret XPS spectra are sometimes not correctly understood or correctly applied. In this review, we not only report on XPS operational parameters in use for fuel cell electrocatalysis, but, more significantly, we review and provide rigorous definitions of fundamental concepts used to understand XPS spectra, including the separation of initial and final state effects and the relaxation of valence electrons to screen core-holes. An additional direction of our review is to show the relationships between XPS binding energy shifts and XPS satellite structure with chemical bonding and chemical interactions. However, our primary concern is to provide reviews of representative cases of the application of XPS to solving fuel cell and electrocatalysis-related problems, highlighting progress in this laboratory. We begin with descriptions of essential issues in fuel cell science and with a review of key concepts of XPS. Then, we briefly report on the XPS instrumentation, after which, studies of fundamental importance to electrochemical processes are reviewed. This review includes an overview of complex organic and biological systems in relation to fuel cell electrocatalysis (probed via XPS). We conclude with a discussion of modern developments in XPS methodology.
    Journal of Power Sources 01/2010; 195(24):7856-7879. · 5.26 Impact Factor
  • C. Wöll, P. S. Bagus, A. Wieckowski
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    ABSTRACT: We present a detailed study of the ionicity of Cs and I adsorbates on a Cu(111) surface and of the consequences of this ionicity for changes in the work function, Δϕ. In particular, a novel aspect of the present work is that we model coverage changes and we are able to determine how coverage increases affect the ionicity and the Δϕ. We use wavefunctions for finite clusters to model the adsorption, where normally only isolated adsorbates are studied. Techniques to simulate coverage were developed. We find and explain unexpected features for the adsorption of I, an excellent electron donor. For I adsorbed at a three-fold site, we confirm earlier results, for I at an on-top site, that the adsorbed Iodine is dominantly anionic with a minor covalent donation from I− to the surface. For the initial increases of coverage, we find that Δϕ has a stronger than linear dependence on the number of adsorbates. We are able to identify the main origin of this super-linear behavior of Δϕ with coverage as changes in the way that the substrate charge polarizes in response to the presence of a higher coverage of adsorbates than to an isolated adsorbate. In particular, the polarization of surface charge at the periphery of the I adsorbate, a kind of pillow effect, is suppressed by the higher density of adsorbates. We present results for different charges of a cluster model for I/Cu that may be relevant for the interpretation of electrochemical measurements of charge flow induced by adsorption of ionic species. Our work presents information relevant for the adsorption of electron donors and acceptors on metal surfaces in general. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 000:000–000, 2010
    International Journal of Quantum Chemistry 01/2010; 110:2844-2859. · 1.17 Impact Factor
  • D.M. Anjos, M.A. Rigsby, A. Wieckowski
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    ABSTRACT: A brief review of the field of underpotential deposition (UPD) processes in the theory/modeling perspective is given, and new insights into the UPD of copper and silver on Rh(1 1 1) and Rh(1 0 0) in perchloric and sulfuric acid media are reported. Voltammetric results show a clear dependence of the UPD shift on Rh substrate geometry and on the type of the electrolyte used. For copper, we identified one peak on Rh(1 0 0) and two peaks on Rh(1 1 1), separated by 210 and 350 mV in perchloric and sulfuric electrolytes, respectively. Preliminary XPS experiments were performed to investigate some specific aspects of copper deposition processes. Overall, we report a strong effect of the anion adsorption on positions of Cu UPD peaks, with the effect being more noticeable on Rh(1 1 1) than on Rh(1 0 0). In the experiments with silver on Rh(1 1 1), multiple peaks were obtained, whereas no Ag UPD peak was found either on Rh(1 0 0) or on polycrystalline Rh. In addition, we found that the Ag UPD process on Rh(1 1 1) is dependent on silver concentration. As indicated in the paper Tables, except for Cu UPD on Rh(1 0 0), there is a major deviation from the linear relationship between the UPD shift and the difference between the work function of the substrate and that for the underpotentially deposited adatoms.
    Journal of Electroanalytical Chemistry. 01/2010; 639:8-14.
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    ABSTRACT: Se/Ru nanoparticles – a potent non-platinum catalyst towards oxygen reduction reaction – were modified by hydrated WO3 and investigated using the rotating disk/ring electrode methods and by synchrotron X-ray photoelectron spectroscopy. The modification resulted in an enhanced catalytic activity towards oxygen reduction reaction (ORR). Our data indicate that the oxygen reduction current starts ca. 70 mV more positive and formation of undesirable hydrogen peroxide has significantly decreased following the modification of Se/Ru with WO3. X-ray photoelectron spectroscopy reveals that WO3 interacts electronically with Se/Ru as the W 4f and Se 3d line-shapes change. We therefore conclude that the electronic interactions between Se/Ru and WO3 are primarily responsible for the increase in activity and selectivity of the WO3-modified Se/Ru towards ORR.
    Electrochimica Acta. 01/2010; 55(26):7603-7609.
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    ABSTRACT: The stability and oxygen reduction activity of two carbon-supported catalyst materials are reported. The catalysts, Se/Ru and Se/(Ru-Mo), were prepared by using a chemical reduction method. The catalyst nanoparticles were evenly dispersed onto globular amorphous carbon supports, and their average size was ca. 2.4 nm. Thermal treatment at 500 °C for 2 h in an inert argon atmosphere resulted in coarsening of the nanoparticles, and also in some decrease of their activity. A gradual reduction of activity was also observed for Se/Ru during potential-cycle experiments. However, the incorporation of small amounts of Mo into the Se/Ru catalysts considerably improved the stability of the catalyst against dissolution. The Mo-containing samples showed excellent oxygen reduction activities even after cycling the potential 1000 times between 0.7 and 0.9 V. Furthermore, they showed excellent fuel-cell behavior. The performance of the Se/Ru catalysts is greatly improved by the addition of small amounts of elemental Mo. Possible mechanisms responsible for the improvement of the activity are discussed.
    ChemSusChem 07/2009; 2(7):658-64. · 7.48 Impact Factor

Publication Stats

2k Citations
405.87 Total Impact Points

Institutions

  • 1986–2013
    • University of Illinois, Urbana-Champaign
      • • Department of Chemistry
      • • School of Chemical Sciences
      • • Department of Chemical and Biomolecular Engineering
      Urbana, Illinois, United States
  • 2009
    • Case Western Reserve University
      • Department of Materials Science and Engineering
      Cleveland, OH, United States
  • 2008
    • University of Virginia
      • Department of Chemical Engineering
      Charlottesville, VA, United States
  • 2005–2008
    • Urbana University
      Urbana, Illinois, United States
  • 2007
    • Los Alamos National Laboratory
      • Sensors and Electrochemical Devices Group
      Los Alamos, NM, United States
  • 2002–2007
    • Georgetown University
      • Department of Chemistry
      Washington, Washington, D.C., United States
  • 2006
    • University of Yamanashi
      • Interdisciplinary Graduate School of Medicine and Engineering
      Kōfu-shi, Yamanashi-ken, Japan
  • 1993–2003
    • University of Illinois at Chicago
      • • Department of Chemical Engineering
      • • Department of Chemistry
      Chicago, IL, United States
  • 1992–2003
    • Purdue University
      • Department of Chemistry
      West Lafayette, IN, United States
  • 1999–2001
    • Czestochowa University of Technology
      • Department of Materials Engineering
      Tschenstochau, Silesian Voivodeship, Poland
  • 1994
    • Florida State University
      Tallahassee, Florida, United States
    • University of Guelph
      • Department of Chemistry
      Guelph, Ontario, Canada