A. Wieckowski

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

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Publications (247)457.48 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
  • Junhua Jiang, John Scott, Andrzej Wieckowski
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    ABSTRACT: Electrooxidation of formate on high-surface Pt black in alkaline media has been studied at varying temperature by means of cyclic voltammetry and stripping voltammetry. In the positive-going scans from 0.10 to 1.2 V vs RHE, the formate oxidation produces three oxidation current peaks: (i) peak I (at potentials where the coverages of both surface hydrogen and oxygen-species are very low), (ii) peak II (exhibiting obvious potential shift from 0.66 to 0.51 V upon increasing temperature from 20 to 80 °C), and (iii) peak III (at higher potentials where a considerable formation of surface oxygen species commences). Both peaks I and II are closely correlated but they are independent of peak III. Among the three peaks, the temperature dependence of peak II is well in agreement with that of the stripping peak of a CO adlayer. These results suggest a triple-path reaction mechanism. Adsorption of formate onto Pt surfaces may result in formation of precursor adsorbates with different reactivity. Analogous to the reported dual-path mechanism, active precursor adsorbate is responsible for (i) a direct path involving the formate oxidation to CO2 (leading to peak I), and (ii) an indirect path involving the formation of surface CO and its further oxidation to CO2 (leading to peak II). An independent third path via oxidation of less-active precursor adsorbate to CO2 with adsorbed HCOO as the most likely intermediate accounts for peak III. All the oxidation reactions involved in the triple paths are accelerated by increasing reaction temperature with different apparent activation energies. At elevated temperature, diffusion-limited oxidation currents are attained. It is suggested that both the activities of surface OH and precursor adsorbates play a major role in mediating the reaction mechanism as well as participating in the formate oxidation.
    Electrochimica Acta 08/2013; 104:124–133. · 4.09 Impact Factor
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    ABSTRACT: Co@Pt/C core–shell catalysts are synthesized by a two-step chemical reduction method followed by the heat treatment in H2 and N2 mixture. High Resolution (HR-TEM), EDX (Energy-dispersive X-ray spectroscopy) and in-situ X-ray diffraction (XRD) techniques are used to characterize the nano-structured catalysts. The results show that the core–shell structure of Co@Pt/C is formed and the average particle size is about 3 nm. From the result of the in-situ XRD, it is found that the heat treatment favors for the formation of crystalline structure and the proper particle size of catalyst. The in-situ XRD detection also helps find the optimized heat treatment temperature. The linear sweep voltammetry (LSV) result reveals that the Co@Pt (1:3)/C (reduced) catalyst exhibits the best catalytic activity toward oxygen reduction reaction (ORR). A 130 h life time test for the single cell, in which the membrane electrode assembly (MEA) using Co@Pt (1:3)/C (reduced) as the cathode catalyst, is operated to evaluate the durability. The results of the test show that the formation of the core–shell structure of Co@Pt/C catalyst is favorable to improve the stability and durability.
    Journal of Power Sources 02/2013; 223:190–198. · 5.26 Impact Factor
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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: a b s t r a c t We co-deposited cobalt porphyrins (CoP) and transition metal oxides on gold and carbon/graphene elec-trodes as catalysts for the oxygen reduction reaction (ORR). Porphyrins were adsorbed spontaneously, and the transition metal oxides (CoO x and NiO x) were deposited using spontaneous deposition tactics or an electrochemical deposition method. The electrodes were characterized in acidic media by cyclic vol-tammetry (CV), by broad-band sum frequency generation (BB-SFG) and – in vacuum – by the Auger elec-tron spectroscopy (AES). The ORR activity data indicate that the activity of cobalt porphyrin towards ORR is enhanced by co-deposited transition metal oxides. The detailed reasons for this behavior are being interrogated. Ó 2013 Elsevier B.V. All rights reserved.
    01/2013;
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    ABSTRACT: In 2007, the field of oxygen reduction reaction (ORR) by porphyrins was partially reviewed by Y. Kiros. The new development reported under the current review is the effect of surface state (composition) on porphyrin’s activity toward oxygen reduction in fuel cells, and the highlight of the analogue of fuel cell cathode activity and the oxygen reduction activity in nature. This field also needs a fresh look vs. its overall importance. The porphyrins themselves are moderate oxygen reduction catalysts, and their activity needs to be enhanced. In perspectives of fuel cells, the methods that are practiced and reviewed here are the use of carbon and gold support, pyrolysis and co-deposition with transition metal oxides. Reasons for the porphyrin enhancements and catalysis have been scrutinized. Although great progress has been achieved, there are still some challenges ahead (concerning the ORR mechanism on porphyrins and the activity and stability enhancement for porphyrins to meet practical applications). Therefore, exploring ORR mechanisms on porphyrin, the continuation of the characterization efforts and enhancing porphyrins catalytic performance (a paper in preparation from this group), as well achieving better catalyst durability, are major focuses for fuel cell research in the future.
    Electrocatalysis. 12/2012; 3(3-4).
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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
  • Junhua Jiang, Andrzej Wieckowski
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    ABSTRACT: A direct formate fuel cell (DFFC) operated with a fuel of alkaline potassium formate has been studied using Pd anode and Ag cathode electrocatalysts in an intermediate temperature range of 80 to 120 °C by means of cyclic voltammetry and single cell measurements. Voltammetric studies clearly show that the kinetics of the formate electrooxidation on Pd in alkaline media is substantially increased with increasing temperature, leading to a high apparent activation energy of around 74.3 ± 6.2 kJ mol− 1. Preliminary single cell measurements show that increasing operating temperature and the formate concentration obviously increase the performance. A DFFC operated with 6 mol dm− 3 HCOOK and at 120 °C demonstrates a peak power density of around 160 mW cm− 2 over a current density range of 250 to 550 mA cm− 2 without Ohmic resistance correction. The DFFC is therefore a promising high performance, environmentally benign and low cost fuel cell technology.
    Electrochemistry Communications 01/2012; 18:41–43. · 4.29 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
    Handbook of Fuel Cells, 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: The continued development of fuel cell technologies, especially for portable and automotive applications, is vital to furthering strategies aimed at addressing current global energy challenges. For widespread market penetration, significant and simultaneous reductions in fuel cell system costs and enhancements in durability are required. Improving oxygen reduction reaction (ORR) catalysis at the fuel cell cathode remains a key challenge. Sluggish kinetics and high overpotentials associated with the ORR hamper both energetic efficiency and peak power production. Furthermore, the high cost and limited availability of platinum (Pt) necessitates the development of alternative catalysts which either reduce or eliminate Pt content. Alloying Pt with transition metals (i.e., M = Co, Ni, Fe) not only reduces catalyst costs by lowering Pt loading but can also increase the ORR activity over pure Pt in acidic media. However, Pt-M alloys may exhibit instability and lose catalytic activity due to transition metal leaching limiting their employment in acidic fuel cell systems. For the development of durable Pt-M alloys, an improved understanding of the local operating environment at the fuel cell cathode is required. Alternatively, with the advent of novel anion-exchange membranes, alkaline fuel cells have gained renewed interest. Operating fuel cells in alkaline media, as opposed to acidic media, is advantageous as enhanced fuel oxidation and oxygen reduction kinetics improve fuel cell energetic efficiency. Furthermore, inexpensive non-Pt catalysts may be used without significant performance reductions. Thus, the development of electrodes, especially cathodes, for use in alkaline media has been the subject of increased focus. To probe the performance and durability of novel cathode catalysts, we use our microfluidic H2/O2 fuel cell with a flowing aqueous electrolyte stream as a catalyst / electrode characterization tool. For analytical investigations, the convecting stream enables autonomous control of electrolyte parameters (i.e., pH, composition), facilitates the removal and downstream analysis of reaction by-products and allows for in-situ monitoring of individual electrode characteristics via an external electrode. Thus, this microfluidic platform enables facilitates detailed in-situ electrochemical analysis of individual catalysts / electrodes within the construct of an operating fuel cell. Here, we investigate the performance and durability of novel cathode catalyst materials over a wide range of fuel cell operating conditions using this analytical platform. We have modified commercially-available Pt3Co catalysts to develop more robust ORR catalysts for acidic fuel cell applications. In particular, we found that a Pt-Co-Mo alloy exhibits enhanced activity and long-term stability compared to commercial Pt3Co and Pt. Furthermore we have studied Ag/C and Cu-triazole catalysts as cheaper alternatives to Pt/C cathodes for alkaline fuel cell applications. Presently, we are further investigating the underlying physical mechanisms that would explain the enhanced activity and stability of some of these ORR catalysts.
    2010 AIChE Annual Meeting; 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;

Publication Stats

2k Citations
457.48 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
    • University of Guelph
      • Department of Chemistry
      Guelph, Ontario, Canada
    • Florida State University
      Tallahassee, Florida, United States
  • 1981–1982
    • University of Warsaw
      • Faculty of Chemistry
      Warszawa, Masovian Voivodeship, Poland