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  • Online Resource  (6)
  • The Electrochemical Society  (6)
  • Chorkendorff, Ib  (6)
  • 1
    Online Resource
    Online Resource
    Elucidating the Pre-Oxygen Evolution Surface Chemistry on Ruthenium Dioxide Surfaces
    The Electrochemical Society ; 2017
    In:  ECS Meeting Abstracts Vol. MA2017-02, No. 47 ( 2017-09-01), p. 2061-2061
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2017-02, No. 47 ( 2017-09-01), p. 2061-2061
    Abstract: The unique interaction between water and rutile Ruthenium Dioxide (RuO 2 ) affords high pseudocapacitance and catalytic activities for a number of reactions such as the oxygen evolution reaction (OER) 1,2,3 . While the low energy, RuO 2 (110) and (100) surfaces have been studied as model systems for gas phase catalysis and ultra high vacuum surface science studies 4,5 , the nature of adsorbed species in aqueous solutions remains to be understood. In this work, we examine the structural and chemical changes occurring on oriented RuO 2 single crystal surfaces as a function of potential, in acidic electrolyte, using in situ  synchrotron-based surface X-ray diffraction (crystal truncation rod) measurements. We find that the positions of the surface Ru and O atoms are largely unchanged from 0.5 V to 1.5 V versus the reversible hydrogen electrode (RHE) scale while adsorbed water molecules on the co-ordinatively unsaturated site (CUS) are deprotonated gradually with increasing potential. At oxygen evolution potentials, we observe the formation of an –OO like group on the co-ordinatively unsaturated site, which is the probable precursor of the evolved oxygen. In order to validate experimentally observed changes in the nature of adsorbed oxygen, we use density functional theory to compute surface Pourbaix diagrams that show the most stable surface termination at any given potential. The experimental and computational results are in strong agreement and provide an atomistic understanding of the surface structural changes associated with the redox transitions prior to oxygen evolution and its implications on the oxygen evolution pathway on RuO 2 . References [1] Trasatti S. Electrochimica Acta. 1984;29(11):1503-1512. [2] Lee Y, Suntivich J, May KJ, Perry EE, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2012;3(3):399-404. [3] Stoerzinger KA, Qiao L, Biegalski MD, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2014;5:1636-1641. [4] Over H. Chemical Reviews. 2012;112(6):3356-3426. [5] Sun Q, Reuter K, Scheffler M. Physical Review B. 2003;67(20):205424.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2017-02/47/2061
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2017
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  • 2
    Online Resource
    Online Resource
    Towards Identifying the Active Sites on Oriented Ruthenium Dioxide Surfaces in Catalyzing Oxygen Evolution
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-01, No. 39 ( 2018-04-13), p. 2287-2287
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-01, No. 39 ( 2018-04-13), p. 2287-2287
    Abstract: The unique interaction between water and rutile Ruthenium Dioxide (RuO 2 ) affords high pseudocapacitance and catalytic activities for a number of reactions such as the oxygen evolution reaction (OER) 1,2,3 . While the low energy, RuO 2 (110) and (100) surfaces have been studied as model systems for gas phase catalysis and ultra high vacuum surface science studies 4,5 , the nature of adsorbed species in aqueous solutions remains to be understood. In this work, we examine the structural and chemical charge transfer processes occurring on oriented RuO 2 single crystal surfaces as a function of potential, in acidic electrolyte, using in situ surface X-ray diffraction measurements. In order to validate experimentally observed changes in the nature of adsorbed oxygen, we use density functional theory to compute surface Pourbaix diagrams that show the most stable surface termination at any given potential. We start with the thermodynamically stable (110) surface, where we show that the coordinatively unsaturated sites (CUS) are the active sites for oxygen evolution. We also detect the formation of an –OO like group on the CUS site, which is the probable precursor of the evolved oxygen. We thus propose a four proton-electron mechanism for OER, where the final proton-electron removal is found to be rate limiting 6 . Using this evidence, we can rationally tune the oxygen evolution reaction (OER) activity of RuO 2 surfaces by modifying the surface structure to increase the density of coordinatively unsaturated sites and optimize the binding strength of oxygenated species on the surface, in order to decrease the energetic barrier of the proposed rate-limiting step. We thus explore different orientations of RuO 2 , namely the (100), (101) and (001) terminations that have a higher CUS site density and lower oxygen binding energy compared to the (110) surface. Using in situ surface X-ray diffraction measurements we can detect the change in the nature of surface adsorbates just prior to OER for the different orientations. Probing the OER active state, supplemented by density functional theory calculations provides insight into the change of the rate limiting step and reaction mechanism for different orientations. Our work shows that modifying the surface orientation is an effective way to tune the active site density and energetics of key OER intermediates to obtain higher activities. Through this synergistic experimental and computational study, we provide an atomistic understanding of charge transfer processes prior to oxygen evolution and its implications on the oxygen evolution pathway on RuO 2 for different surface orientations. References [1] Trasatti S. Electrochimica Acta. 1984;29(11):1503-1512. [2] Lee Y, Suntivich J, May KJ, Perry EE, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2012;3(3):399-404. [3] Stoerzinger KA, Qiao L, Biegalski MD, Shao-Horn Y. The Journal of Physical Chemistry Letters. 2014;5:1636-1641. [4] Over H. Chemical Reviews. 2012;112(6):3356-3426. [5] Sun Q, Reuter K, Scheffler M. Physical Review B. 2003;67(20):205424. [6] Rao RR, et al., Energy & Environmental Science, 2017, DOI: 10.1039/C7EE02307C (accepted)
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-01/39/2287
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 3
    Online Resource
    Online Resource
    (Invited) Microreactors for Characterization and Benchmarking of Photocatalysts
    The Electrochemical Society ; 2015
    In:  ECS Meeting Abstracts Vol. MA2015-01, No. 27 ( 2015-04-29), p. 1611-1611
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2015-01, No. 27 ( 2015-04-29), p. 1611-1611
    Abstract: In the field of photocatalysis the batch-nature of the typical benchmarking experiment makes it very laborious to obtain good kinetic data as a function of parameters such as illumination wavelength, irradiance, catalyst temperature, reactant composition, etc.  Microreactors with on-line mass spectrometry, on the other hand, allow fast and automated acquisition of quantitative kinetic data. [1,2] As an example, we show how microreactor experiments on water splitting using Pt- or Rh-loaded GaN:ZnO photocatalysts quickly rank different catalysts according to their activity for gas-phase water splitting - but also how the activity scales with relative humidity and the crucial role of CrOx "capping" of the Pt- or Rh-co catalyst in order to prevent the loss of H2/O2 product via backward reaction on the precious metal. [3,4] The data suggests that protons transfer via the catalyst surface between the oxygen-evolving sites and the hydrogen evolving co-catalyst sites.  Recently, the microreactor experimental platform is being developed to support in-situ UV-VIS-IR spectroscopy [5] and even the introduction of liquid aqueous electrolyte and electrodes - all while retaining high sensitivity time resolved mass spectrometric product detection. [6] [1] Vesborg et al. Chemical Engineering Journal, 160, p. 738-741 (2010) [2] Vesborg et al. J. Phys. Chem. C, 114, p. 11162-11168 (2010) [3] Dionigi et al. Energy & Env. Sci., 4, p. 2937-2942 (2011) [4] Dionigi et al. J. Catal., 292, p. 26-31 (2012) [5] Dionigi et al. Rev. Sci. Instr., 84, p. 103910 (2013) [6] Bøndergaard et al. "Fast and sensitive method for detecting volatile species in liquids", submitted
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2015-01/27/1611
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2015
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  • 4
    Online Resource
    Online Resource
    In-Situ XRD during Electrochemical CO Reduction on Cu
    The Electrochemical Society ; 2018
    In:  ECS Meeting Abstracts Vol. MA2018-01, No. 28 ( 2018-04-13), p. 1612-1612
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2018-01, No. 28 ( 2018-04-13), p. 1612-1612
    Abstract: Almost all-successful CO 2 and CO reduction catalysts to higher chain carbons are based on copper, 1 however various facets and pre-treatments of copper have shown to give a wide variety of product selectivity. 2, 3 Currently there are many unanswered questions regarding active sites and mechanisms thus fundamental studies are essential for this reaction. This talk will focus on in-situ monitoring the copper-copper oxide crystal structure at a variety of oxidative and reductive potentials. Using the synchrotron facilities at the SLAC national laboratory we were able to achieve an in-depth understand both of how deep the native oxide layer penetrates and how this oxide becomes reduced as we shift towards more cathodic potentials. This talk was also discuss under what conditions there is an amorphous copper oxide layer and what conditions lead to a crystalline copper oxide surface. This will be followed by a discussion of how the copper oxide effects the crystal structure of the metallic copper at the operating conditions. The in-situ work focused on a preferentially oriented 〈 111 〉 thin film, however there were other facets to a lesser extent. This talk will discuss the degree to which these facets are modified during in-situ operating conditions at various potentials. Hori, Y.; Wakebe, H.; Tsukamoto, T.; Koga, O., Electrocatalytic Process of CO Selectivity in Electrochemical Reduction of CO2 at Metal-Electrodes in Aqueous Media. Electrochimica Acta 1994, 39 (11-12), 1833-1839. Li, C. W.; Ciston, J.; Kanan, M. W., Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature 2014, 508 (7497), 504-+. Hori, Y.; Takahashi, I.; Koga, O.; Hoshi, N., Electrochemical reduction of carbon dioxide at various series of copper single crystal electrodes. Journal of Molecular Catalysis a-Chemical 2003, 199 (1-2), 39-47.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2018-01/28/1612
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2018
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  • 5
    Online Resource
    Online Resource
    Enhancement of Lithium-Mediated Ammonia Synthesis By Addition of Oxygen
    The Electrochemical Society ; 2022
    In:  ECS Meeting Abstracts Vol. MA2022-01, No. 40 ( 2022-07-07), p. 1811-1811
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2022-01, No. 40 ( 2022-07-07), p. 1811-1811
    Abstract: Ammonia is one of the most produced chemicals worldwide and is currently synthesized by the Haber-Bosch process, which is a thermally catalyzed method that requires high pressures and temperatures. These harsh conditions, in addition to the prerequisite steam reforming process, leads to about 1 % of the annual energy consumption and 1.4 % of the global CO 2 emission. One way to mitigate some of the Haber-Bosch process is to produce ammonia electrochemically, utilizing renewable energy sources. The electrochemical synthesis of ammonia faces several big issues. One being the selectivity, since the more facile hydrogen evolution reaction (HER) will always dominate over the nitrogen reduction reaction (NRR), and another issue being the activity, given that the nitrogen triple bond is very stable and therefore hard to split. Hence, most often the reported ammonia contents are in the low ppm regime, which makes it very susceptible to contaminations both from the gas stream (NH 3 and NO x impurities) and the system itself (catalyst, cell, chemicals, nitrile gloves, etc.). To avoid misleading results, several protocols have been published on how to correctly perform NRR experiments [1, 2]. One of these confirm that only the Li-mediated ammonia synthesis (LiMeAS) is currently able to produce ammonia electrochemically [3] . The actual mechanism is not fully understood, but it is generally believed that the first step is Li plating from a Li salt containing non-aqueous electrolyte. The very reactive Li will then react with N 2 solvated in the electrolyte to form Li 3 N, which is believed to hydrolyze to ammonia when in contact with a proton source. The currently highest archived faradaic efficiency (FE) is at 69 % at 20 bar N 2 pressure when applying an ionic liquid as a proton shuttle [4]. In this work, we achieved up to 79 % FE at 20 bar N 2 by the addition of 0.8 mol. % O 2 in the reaction atmosphere. The positive effect of O 2 is a very counterintuitive observation, since the original work by Tsuneto et al. [5] showed that the use of synthetic air significantly hindered the reaction, as it was postulated that O 2 inhibits the reaction due to LiO 2 formation and/or leading primarily to the oxygen reduction reaction (ORR). We will present experimental results obtained at 10 and 20 bar with varying O 2 contents, which were measured accurately by a mass spectrometer probing the atmosphere just above the electrolyte inside the pressure vessel. By combining experimental observations with theoretical modelling, we conclude that the unexpectedly beneficial role of small O 2 concentrations has a positive influences the solid electrolyte interface (SEI), which is of great importance in our system. Additional ex-situ X-Ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS) measurements were conducted without exposure to air and moisture, to analyze the SEI layer and deposition after electrochemistry. We believe that this study will not only be beneficial for industrializing the LiMeAS, but will also bring us a step further in understanding the complex mechanism behind this process. [1] S. Z. Andersen et al. , "A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements," Nature, vol. 570, pp. 504-508, 2019. [2] H. Iriawan et al. , "Methods for nitrogen activation by reduction and oxidation," Nature Reviews Methods Primers, vol. 1, no. 1, pp. 1-26, 2021. [3] J. Choi et al. , "Identification and elimination of false positives in electrochemical nitrogen reduction studies," Nature communications, vol. 11, no. 1, pp. 1-10, 2020. [4] B. H. Suryanto et al. , "Nitrogen reduction to ammonia at high efficiency and rates based on a phosphonium proton shuttle," Science, vol. 372, no. 6547, pp. 1187-1191, 2021. [5] A. Tsuneto, A. Kudo, and T. Sakata, "Lithium-mediated electrochemical reduction of high pressure N2 to NH3," Journal of Electroanalytical Chemistry, vol. 367, no. 1-2, pp. 183-188, 1994.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2022-01401811mtgabs
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2022
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  • 6
    Online Resource
    Online Resource
    Correlating Structure and Oxygen Reduction Activity on Y/Pt(111) and Gd/Pt(111) Single Crystals
    The Electrochemical Society ; 2015
    In:  ECS Meeting Abstracts Vol. MA2015-03, No. 3 ( 2015-07-15), p. 668-668
    Details
    In: ECS Meeting Abstracts, The Electrochemical Society, Vol. MA2015-03, No. 3 ( 2015-07-15), p. 668-668
    Abstract: Polymer Electrolyte Membrane Fuel Cells (PEMFC) hold promise as a zero-emission source of power, particularly suitable for automotive vehicles. However, the high loading of Pt required to catalyse the Oxygen Reduction Reaction (ORR) at the PEMFC cathode prevents the commercialisation of this technology. Improving the activity of Pt by alloying it with other metals could decrease the loading of Pt at the cathode to a level comparable to Pt-group metal loading in internal combustion engines. Pt x Y and Pt x Gd exhibit exceptionally high activity for oxygen reduction, both in the polycrystalline form and the nanoparticulate form. [1,2,3,4]. Moreover, their negative alloying energy may make them inherently less prone to degradation via dealloying than the more commonly investigated alloys of Pt and late transition metals such as Ni, Co, Fe and Cu. In order to understand the origin of the enhanced activity of these alloys, we have investigated Y/Pt(111) [5] and Gd/Pt(111) single crystals, formed by depositing large amounts of Y and Gd on Pt(111) single crystals under Ultra-High Vacuum (UHV) conditions and annealing to high temperatures.  We subsequently characterised the surface using low energy electron diffraction, ion scattering spectroscopy and temperature programmed desorption of CO.  After the characterization in UHV, the ORR activity was measured. Angle resolved X-ray photoelectron spectroscopy measurements were carried out after the electrochemical measurements. These experiments revealed, that thick platinum overlayers had been formed, and that the structure formed under reaction conditions was significantly different from our initial expectations. The structures of the overlayers were investigated using surface sensitive X-ray diffraction using synchrotron radiation, and correlated to the oxygen reduction activity. [1] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B. P. Knudsen, A. K. Jepsen, J. Rossmeisl, I. E. L. Stephens, and I. Chorkendorff,   Journal of the American Chemical Society , 134(40):16476–16479, Oct 10 2012. [2] J. Greeley, I.E.L. Stephens, A.S. Bondarenko, T.P. Johansson, H.A. Hansen, T.F. Jaramillo, J. Rossmeisl, I. Chorkendorff, J.K. Nørskov, Nature Chemistry , 1 (2009) 552-556. [3] A. Velázquez-Palenzuela, F. Masini, A. F. Pedersen, M. Escudero-Escribano, D. Deian, P. Malacrida, T. W. Hansen, D. Friebel, A. Nilsson, I. E. L. Stephens, I. Chorkendorff, J. Catal. 2015, in press. [4] Hernandez-Fernandez, P., Masini F., McCarthy D. N., Strebel C. E., Friebel D., Deiana D., Malacrida P., Nierhoff A., Bodin A., Wise A. M., Nielsen J. H., Hansen T. W., Nilsson A., Stephens I. E. L., and Chorkendorff I. Nat Chem, 6(8): 732-738, Aug 2014 [5] T. P. Johansson, E. T. Ulrikkeholm, P. Hernandez-Fernandez, M. Escudero-Escribano,P. Malacrida, I. E. L. Stephens, and I. Chorkendorff. Physical Chemistry Chemical Physics, 16(27):13718–13725, 2014.
    Type of Medium: Online Resource
    ISSN: 2151-2043
    URL: Article
    DOI: 10.1149/MA2015-03/3/668
    Language: Unknown
    Publisher: The Electrochemical Society
    Publication Date: 2015
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