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New frontiers for the in-situ and operando spectroscopic investigation of interfaces applied to catalysis and electrochemistry

This symposium will focus on the characterization of catalytically- and electrochemically- relevant interfaces by means of in situ and operando spectroscopies. Recent advances in the use of single and combined spectroscopic methods (photoemission, absorption, IR, Raman, etc,) will be presented and perspectives will be discussed.

Scope

Interfaces are of fundamental importance to understand the behavior of catalytic and electrochemical materials under reaction conditions. Spectroscopic methods are often used to investigate such materials because they allow qualitative and/or quantitative characterization under reactive environments without perturbing the reaction. Among them, synchrotron-based techniques, such as absorption, emission and photoemission spectroscopy, and “laboratory-based” techniques, such as Infrared and Raman spectroscopy, have been developed. By means of such techniques it is possible to obtain an in situ characterization of a material, that is, exposing it to a reactive environment under realistic working conditions while simultaneously acquiring information about the evolution of its physical-chemical and morphological properties. At the same time, operando measurements, carried out on materials undergoing a reaction while measuring the catalytic activity/selectivity and product pattern, are extremely useful to determine the structure-chemical composition-reactivity relationships. The main goal of this symposium is to merge the research communities investigating catalytic and electrochemical interfaces with different in situ/operando spectroscopic techniques to share and discuss recent results, methods and perspectives. The development of time- and space-resolved in situ/operando spectroscopic investigations will also be a paramount topic. The symposium will be a unique opportunity to foster the collaboration among groups having different expertise, to attract potential users developing materials whose novel properties need to be characterized, and to introduce recently developed experimental setups employing more than one spectroscopic method at the same time.

Papers focused on the investigation of catalytic and electrochemical interfaces by means of in situ and operando spectroscopic methods are invited and will be published in a special issue of “Catalysis Today”.

 
Hot topics to be covered by the symposium
  • In situ and operando spectroscopic investigation of reactive interfaces (XPS, XAS, XES, IR, Raman)
  • Time and space-resolved spectroscopic investigation of reactive interfaces under  realistic working conditions
  • Development of new in situ and operando spectroscopic methods
  • Development of new experimental setups employing more than one spectroscopic method for the in situ and operando investigation of reactive interfaces (both laboratory- and synchrotron-based).

Operando spectroscopic techniques as high-throughput materials research boosters

 

List of confirmed invited speakers

  • B. Weckhuysen (University of Utrecht, Utrecht, The Netherlands),
  • Junko Yano (LBNL, California, USA)
  • Miguel A. Bañares (Instituto de Catalisis, CSIC, Madrid, Spain),
  • Ib Chorkendorff (Technical University of Denmark, Kongens Lyngby, Denmark
  • Zhi Liu (ShanghaiTech University, Shanghai, China)
  • Anja Bieberle (Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands)
  • Philipp Stadler(Institute of Physical Chemistry and Linz Institute of Organic Solar Cells, Johannes Kepler University, Linz, Austria)
  •  

List of confirmed scientific committee members

  • Joachim Schnadt (Lund University – MAX IV, Sweden
  • Jeroen van Bokhoven (ETH Zurich – PSI Villigen, Switzerland
  • Robert Weatherup (The University of Manchester at Harwell, U.K.)
  • Ashley Head (Center for Nanoscience and Nanomaterials, LBNL, USA)
  • David Starr (HZB, Berlin, Germany)
  • Ian Sharp (WSI – TUM, Munich, Germany)
  • Georg Held (University of Reading, Diamond Synchrotron, U.K.)
  • Luca Gregoratti (Elettra Synchrotron, Italy)
  • Karin Föttinger (TU Wien, Austria)
  • Giovanni Agostini (ALBA Synchrotron, Barcelona, Spain)
  • Andrea Zitolo (SOLEIL Synchrotron, Paris, France)
  • Patricia Conception (Spanish National Research Council, Spain)
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09:00 Welcome - Luca Artiglia, Virginia Perez-Dieste, Marco Favaro    
 
Imaging and Spectroscopy : Luca Artiglia
09:10
Authors : Bert M. Weckhuysen
Affiliations : University of Utrecht, Debye Institute for Nanomaterials Science, Inorganic Chemistry and Catalysis, David de Wiedgebouw Universiteitsweg 99, 3584 CG Utrecht

Resume : Catalysts Live & Up Close Bert M. Weckhuysen, Inorganic Chemistry and Catalysis group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands; b.m.weckhuysen@uu.nl Abstract The search for new or more effective heterogeneous catalysts would benefit when we could bridge the molecular world with the macroscopic world. Such detailed information can be realized if we would have access to a very powerful camera shooting molecular movies of an active catalytic solid at the level of single atoms and molecules. This is the field of operando spectroscopy. Recent breakthroughs in chemical imaging techniques, based on optical, electron and X-ray methods, demonstrate that such molecular movie concept is within reach. This lecture discusses the recent advances in spectroscopy and microscopy of heterogeneous solids at different length scales, starting from single molecules and single atoms up to the level of individual catalyst particles. Special emphasis will be devoted to the exploration of mesoscale effects as well as on the scientific challenges ahead to make such molecular movie reality. It will be shown how this better understanding of catalytic processes may be beneficial for transforming our society to a more sustainable one. The critical concept of such much needed transition towards a circular economy should be: reduce, reuse & recycle.

S.1.1
09:45
Authors : Matteo Amati, Patrick Zeller, Luca Gregoratti
Affiliations : Elettra – Sincrotrone Trieste S.C.p.A di interesse nazionale, Strada Statale 14 - km 163,5 in AREA Science Park, 34149 Basovizza, Trieste ITALY

Resume : Due to the short escape depth of electrons, less than a few nm, photoelectron spectroscopy is the best surface sensitive analytical techniques for probing surface and interface chemical composition, but the investigation of complex systems in electrochemistry and catalysis requires not only near ambient pressure (NAP) conditions, but often the samples are inhomogeneous at the submicron scale. The authors have developed photoemission imaging and spectromicroscopy methodology based on the Scanning PhotoEmission Microscope (SPEM) to simultaneously overcome the two limitations of the XPS technique, i.e. lack of spatial resolution and UHV requirements [1]. This solution allow chemical and morphological analysis providing information under operation conditions. SPEM uses a direct approach to add the spatial resolution to XPS i.e a small focused X-ray photon probe to illuminate the sample. The focusing of the X-ray beam is performed by Zone-Plates and samples surface is mapped by scanning the sample with the focused beam. X-ray beam can be downsized to a diameter of 130 nm, allowing imaging resolution of less than 50 nm with an energy resolution of 200 meV. To overcome the UHV requirement effusive cells where high- and low-pressure regions are separated by small apertures of few hundreds micrometers, for photons delivery and photoelectrons collection, was developed. The pressure inside the cell can be raised up to mbar while the pressure in the main chamber remain in HV. Four isolated electrical connections are available for heating and biasing of sample. Results on the in-situ and operando studies performed at the Escamicroscopy beamline@ ELETTRA synchrotron will be presented [1]. [1] http://dx.doi.org/10.1007/s11244-018-1064-5

S.1.2
10:05
Authors : Lukas Pielsticker, Rachel L. Nicholls, Mark T. Greiner, Robert Schlögl
Affiliations : Max-Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, Mülheim an der Ruhr, Germany

Resume : X-ray spectromiscroscopy methods are frequently used for the spatially-resolved in situ characterization of heterogeneous catalysts. However, the choice of the region to be investigated during the measurements and the identification of spectral features during data analysis is often not trivial. Here we demonstrate the use of an unsupervised machine learning technique called cluster analysis to identify and classify regions of interest on the sample surface. Different clustering methods such as k-means clustering, spectral clustering and density-based clustering were evaluated with respect to their success of identifying areas of chemical contrast from scanning photoelectron microscopy (SPEM) and X-ray photoemission electron microscopy (XPEEM) images. It was shown that the use of spectral clustering provides a robust tool for identifying the spatial distribution of complex features with a low signal-to-noise ratio, which are often present in spectral images acquired under near-ambient pressure conditions. This work enables the analysis of spectromiscroscopy data on the fly during fast measurements at the synchrotron, as well as the advanced analysis of convoluted spectral images afterwards.

S.1.3
10:30 Coffee Break    
 
Spectroscopy and Carbon Dioxide Reduction : Virginia Perez-Dieste
11:00
Authors : Yifan Ye (1,2,3), Jin Qian (4), Hao Yang (4), Hongyang Su (2,5), Kyung-Jae Lee (2,6), Tao Cheng (4,7), Hai Xiao (4,7), William A. Goddard III (4,7), Ethan J. Crumlin (2), Junko Yano (1,8)
Affiliations : (1) Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, United States, (2) Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, United States, (3) Chemical Sciences Division, Lawrence Berkeley National Laboratory, United States, (4) Materials and Process Simulation Center, California Institute of Technology, United States, (5) Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, P. R. China, (6) Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Gwangju, South Korea, (7) Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, United States, (8) Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, United States

Resume : X-ray techniques play an important role for gaining the fundamental understanding needed to tailor novel catalysts for CO2 reduction reaction (CO2RR), by providing chemical and structural information of catalytic surfaces. We have utilized surface-sensitive soft and hard X-ray techniques to investigate the interaction of metal catalytic surfaces with electrolytes and/or gases (H2O and/or CO2) under in situ/operando conditions at the Stanford Synchrotron Radiation Lightsources (SSRL) and Advanced Light Source (ALS). We present here our work on Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS) for studying CO2 adsorption on Cu and Ag surfaces to understand the initial atomic level events for CO2 electroreduction on the metal catalysts, and CO2 adsorption on Ag/Cu alloys to provide the basis for developing improved catalysts electrolyte/solid catalytic surfaces, as well as surface studies of the catalyst/electrolyte surfaces.

S.2.1
11:35
Authors : Philipp Stadler
Affiliations : Linz Institute of Technology and Institute of Physical Chemistry, Johannes Kepler University Linz, Austria

Resume : Recent progress in the field of electrocatalytic CO2 reduction have brought up several classes of novel catalytic systems such as polymers and various metal chalcogenides1,2. These materials possess excellent catalytic activity, but still little is known about the exact catalytic centers and the exact mechanisms leading to efficient turnover. Here we present internal reflection mode infrared spectroscopy as valuable in-situ technique for emerging CO2 electrocatalysts. We demonstrate the exact spectroscopic characterization of the intermediate surface states and conclude on their impact on the Faradaic and energy efficiency. In combination with theoretical modelling in-situ spectroelectrochemistry represents one complementary experimental technique to determine the reaction mechanisms. These insights are useful to develop alternative catalytic materials with improved surface activity and selectivity beyond CO and formate. (1) Zheng, X.; De Luna, P.; García de Arquer, F. P.; Zhang, B.; Becknell, N.; Ross, M. B.; Li, Y.; Banis, M. N.; Li, Y.; Liu, M.; Voznyy, O.; Dinh, C. T.; Zhuang, T.; Stadler, P.; Cui, Y.; Du, X.; Yang, P.; Sargent, E. H. Sulfur-Modulated Tin Sites Enable Highly Selective Electrochemical Reduction of CO2 to Formate. Joule 2017 DOI: 10.1016/j.joule.2017.09.014. (2) Coskun, H.; Aljabour, A.; De Luna, P.; Farka, D.; Greunz, T.; Stifter, D.; Kus, M.; Zheng, X.; Liu, M.; Hassel, A. W.; Schöfberger, W.; Sargent, E. H.; Sariciftci, N. S.; Stadler, P. Biofunctionalized Conductive Polymers Enable Efficient CO2 Electroreduction. Sci. Adv. 2017, 3 (8), e1700686 DOI: 10.1126/sciadv.1700686.

S.2.2
12:10 Lunch Break    
 
AP-HAXPES to probe the solid-liquid interface : Marco Favaro
14:00
Authors : Zhi Liu
Affiliations : School of Physical Science and Technology,ShanghaiTech University, China; Shanghai Institute of Microsystem and Information Technology, CAS, China E-mail: liuzhi@shanghaitech.edu.cn

Resume : Direct probing solid-liquid interface is the first step to truly understand an electrochemical system, where the electrochemical interface plays a crucial role. However, it has been a challenge to look through the dense liquid or solid layer and to monitor the thin electrochemical interface while the electrochemical reactions are happening. Many groups have tried to use different in-situ techniques to address this challenge. Particularly, several significant advances have been made recently to probe the electrochemical interface under in situ and operando conditions using synchrotron radiation based characterization tools. Ambient pressure X-ray photoelectron spectroscopy (APXPS) is one of them [1]. In this talk, I will give a brief history how our group developed APXPS techniques using tender X-ray to probe the electrochemical interface directly [2] and show several in-situ studies [3,4] on electrolyte/electrode interfaces and aqueous solutions. At the end, I will share the progress that we have made on X-ray free electron laser development in Shanghai. References [1] X. Liu et. al., Advanced Materials 26 (46), 7710-7729 (2014) [2] S. Axnanda et. al, Scientific Reports, 5,9788 (2015) [3] M. F. Lichterman et. al, Energy & Environmental Science 8 (8), 2409-2416 (2015) [4] M. Favaro et. al, Nature communications 7, 12695 (2016)

S.3.1
14:35
Authors : Michael J Sear, Marco Favaro, Pip CJ Clark, Roel van de Krol, David E Starr
Affiliations : Helmholtz Zentrum Berlin fuer Materialien und Energie GmbH.

Resume : Ambient pressure hard x-ray photoelectron spectroscopy (AP-HAXPES) has been used to study the interaction of several electrolytes with the surface of bismuth vanadate (BiVO4), a technologically relevant water-splitting photoelectrode material. Structural changes in the surface and electrolyte were seen under illumination, which were dependent on the chosen electrolyte. The development of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) has enabled the study of material surfaces at realistic pressures. While many studies have used soft x-ray XPS to study solid-gas interfaces, the attenuation length of electrons at this energy range can be limiting. The recent application of the tender or hard x-ray energy range to ambient pressure XPS (i.e. AP-HAXPES) allows the investigation of buried interfaces, including solid-liquid interfaces. We have applied this technique to the BiVO4 – electrolyte interface. In this study, a liquid layer of electrolyte was formed on the surface of thin film BiVO4 by the dip-and-pull method, and the resulting solid – liquid interface probed by AP-HAXPES under illumination by a solar simulator. Using potassium phosphate, we observed spectral changes consistent with the formation of bismuth phosphate, and concurrent restructuring of the electrolyte. Like changes were absent when illuminating a similar layer of potassium borate. This study offers insight into the effect of electrolyte choice on device stability and demonstrates the value of AP-HAXPES as a tool for probing solid-liquid interfaces.

S.3.2
14:55
Authors : Robert Wenisch1, Tim Kodalle1, Natalia Maticiuc1, Yajie Wang1, Tobias Bertram1, Hasan A.Yetkin1, Jérome Deumer1, Silvio Knoop1, Christian A. Kaufmann1, Rutger Schlatmann1,2, Iver Lauermann1
Affiliations : 1 Helmholtz-Zentrum Berlin für Materialien und Energie PVcomB; 2 Hochschule für Technik und Wirtschaft Berlin

Resume : Cu(In,Ga)Se2 (CIGS)-based photovoltaic cells have been demonstrated to be excellent bottomcells in perovskite-based tandem devices for enhanced power-conversion efficiency [1,2]. However, the low temperature resilience of the standard CIGS/CdS interface limits the choice of materials and further processing window for the top cell. This study aims to analyze the degradation mechanisms responsible for the premature deterioration of the buffer and interface. Additionally, an alternative Zn(O,S) buffer-layer and possible effects of a RbF post-deposition treatment (PDT) on either of these interfaces are investigated. The study employs in-situ, synchrotron-based hard X-ray photoelectron spectroscopy. The substrate temperature was slowly ramped up (0.5°C/min), covering a range from 150°C-350°C, which results in a quasi-continuous temperature resolution. The measurements covered all relevant elements (Cu, In, Ga, Se, Na, Cd, Zn, O, S), ensuring that degradation temperature and mechanism can be identified. RbF PDT delayed the buffer deterioration for CdS buffers, while the degradation of Zn(O,S) buffers was found to be accelerated. Furthermore, RbF PDT-induced Na depletion of the absorber and delayed Na diffusion are found in this study. [1] Qifeng Han Science 31, 2018:, pp. 904-908 DOI: 10.1126/science.aat5055. [2] M. Jošt et al., ACS Energy Lett. 4, 2019, pp 583–590 DOI: 10.1021/acsenergylett.9b00135.

S.3.3
15:30 Coffee Break    
 
Characterize the solid-liquid interfaces with XPS and XAS : Zhi Liu
16:00
Authors : Rik Mom, Lorenz Frevel, Juan Velasco-Velez, Travis Jones, Axel Knop-Gericke, Robert Schlögl
Affiliations : Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany

Resume : To probe active electrocatalyst surfaces in a liquid environment, we have developed an XPS/XAS cell in which the catalyst is confined between a proton exchange membrane and graphene. While the proton exchange membrane supplies a steady flow of electrolyte to the electrode, the X-ray and electron-transparent graphene layer greatly reduces the evaporation of water into the NAP-XPS chamber. We show that this can lead to the formation of a thin layer of liquid electrolyte between the graphene and the membrane. Thus, electrocatalysts can be studied under operating conditions using surface sensitive soft X-ray XPS and XAS [1]. With this methodology, we have studied the potential-driven restructuring of Ru, Ir and Au oxides in 0.1 M H2SO4 during the oxygen evolution reaction. While for AuOx only Au3+ is found, the electronic structure of the Ru and Ir cations is dynamic, particularly for Ru. O K-edge spectra, complemented by theory, indicate that the oxidation of the catalysts occurs through deprotonation, even in the bulk of the materials. The deprotonation proceeds through multiple stages: hydroxyl groups with higher coordination deprotonate at lower potential. Interestingly, we find that deprotonation is not complete during the oxygen evolution reaction on Ru and Ir. [1] Mom et al., J. Am. Chem. Soc., 2019, 141 (16), pp 6537–6544

S.4.1
16:20
Authors : Silvia Nappini (a), Elena Magnano (a), Federica Bondino (a), Igor Píš (a,b), Alessia Matruglio (c), Simone Dal Zilio (a), Denys Naumenko (b), Marco Lazzarino (a)
Affiliations : (a) CNR-IOM, Laboratorio TASC, S.S. 14-km 163.5, 34149 Basovizza, Trieste, Italy (b) Elettra-Sincrotrone Trieste S.C.p.A, S.S. 14-Km 163.5,34149 Basovizza, Trieste, Italy (c) CERIC-ERIC, S.S. 14-Km 163.5, 34149 Basovizza,Trieste, Italy

Resume : The investigation of processes at the solid/liquid or solid/gas interfaces is of paramount importance in many fields, including catalysis, electro-chemistry and energy. Synchrotron-based spectroscopic techniques, such as X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Absorption Spectroscopy (XAS) can offer a comprehensive understanding of the electronic properties of materials in atmospheric conditions or in liquid environment, providing information on the electron transfer processes at the interfaces during catalytic reactions. Cells based on graphene and Si3N4 membranes have been demonstrated to work as soft X-ray transparent interface between liquid and vacuum. Sealed graphene nanobubbles (GNBs) on a titanium dioxide TiO2 (100) rutile single crystal filled with different aqueous solutions were developed and characterized by AFM, Raman and synchrotron radiation spectroscopies. GNBs were successfully employed to follow in-situ two reactions: thermal-induced reduction of FeCl3 to FeCl2, and photo-induced reduction of ferromagnetic Prussian Blue to paramagnetic Prussian White in aqueous solution. The electronic states of iron atoms in both systems and the presence of solvent were obtained through a combination of XPS and XAS measurements, which allowed the comprehension of the electron reduction mechanisms and the role of water in both processes. A cell, equipped with a 100 nm thick Si3N4 window, was developed to perform in-situ XAS measurements in liquid phase. The effect of the solvent in the unoccupied electronic structure of iron and cobalt atoms, as well as the changes in the local charge and coordination state of CoFe2O4 nanoparticles suspended in aqueous solution were investigated by fluorescence yield XAS.

S.4.2
16:40
Authors : Conor Byrne, Khadisha Zahra, Alex Walton
Affiliations : School of Chemistry, University of Manchester, Manchester M13 9PL Photon Science Institute, University of Manchester, Manchester M13 9PL

Resume : Here we demonstrate the proof of principal and initial results of performing operando XPS electrochemistry in a lab based near atmospheric pressure (NAP) XPS system utilising a standard lab based monochromatic aluminium source. A thin capillary is used inside the NAP-Cell in conjunction with a simple custom built electrochemistry cluster in order to advance and recede droplets onto a sample surface. Small volumes of solution have been dispensed on surfaces in vacuum and ultra-thin liquid layers (<10 nm) have been shown to allow analysis of the solid/liquid interface all whilst allowing electrochemical control, thereby creating a lab based operando XPS electrochemical set-up. Novel features such as in-situ sample rinsing and the ability to modify the chemical properties of the electrolyte during analysis by pulsing various liquid solutions into the analysis droplet boost the appeal of this technique when compared to other available operando techniques. Analysis of the solid/liquid interface has been performed on a number of samples such as TiO2, Pt and Fe in addition to analysis of bulk electrolyte solutions.

S.4.3
17:00
Authors : Liana Socaciu-Siebert, Paul Dietrich, Andreas Thissen
Affiliations : SPECS Surface Nano Analysis GmbH, Berlin, Germany

Resume : Over the last decades XPS under Near Ambient Pressure (NAP) conditions has demonstrated its promising potential in a wide variety of applications. Starting from operando studies of surface reactions in catalysis, the applications soon have been enhanced towards studies of processes at liquid surfaces, mainly using freezing/melting cycles, liquid jets or liquid films on rotation disks or wheels. Since more than 15 years, the need for basic studies of the fundamental chemistry at solid-liquid interfaces has attracted growing interest. Dip-and-pull experiments at synchrotrons finally also demonstrated, that in-situ and operando XPS in electrochemical experiments can be realized, mainly using synchrotron beams, significantly contributing to the basic understanding of modern energy converting or storing devices, like batteries, fuel cells, etc. The development of pure laboratory NAP-XPS systems with optimized sample environments, like special sample holders, Peltier coolers and operando liquid cells combined with full automation and process control provides possibilities for the preparation and analysis of a multitude of liquid samples or solid-liquid interfaces on a reliable daily base. Interfaces of semiconductors with organic solvents are important for production processes and device operation. The first example presented shows the simplicity of obtaining relevant results on Silicon in different organic solvents without the need of highly sophisticated setups or special excitation sources beyond Al K alpha. The next level of complexity is to follow the effects of corrosion in organic or inorganic acids. As an example an operando study of metal corrosion in acetic acid is shown. Most sophisticated experiments so far have been operando electrochemistry in a classical three-electrode setup. A versatile setup is presented, allowing for studies of solid-electrolyte interfaces for example in Lithium ion batteries as a simple laboratory experiment. Finally an outlook is given on the future perspective of applications and scientific contributions of routine operando XPS.

S.4.4
 
Poster Session : Luca Artiglia, Marco Favaro, Virginia Perez-Dieste
17:30
Authors : Dennis Hein*°, Garlef Wartner*°, Martin Schellenberger*°, Robert Seidel*°
Affiliations : *Helmholtz-Zentrum Berlin, Albert-Einstein-Straße 15, 12489 Berlin, Germany °Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, 12489 Berlin, Germany

Resume : Converting solar or electric energy into chemical energy contained in the hydrogen bonds is a promising approach for long time storage of energy. However, the Oxygen Evolution Reaction (OER) limits the conversion efficiency of this process, because even the overpotentials of the best-known catalysts for water splitting remain quite high. To overcome this obstacle, better suited materials containing inexpensive, corrosion-resistant, and abundant elements are required. For rational design of new OER catalysts, an in-depth comprehension of the underlying conversion processes at the solid liquid interface is crucial. We apply operando photoelectron spectroscopy (PES) that reveals details of the OER mechanism of well-known catalytically active transition-metal oxides, e.g. iron-nickel oxy-hydroxides. We will present first experimental results from our newly developed (photo)electrochemical flow-cell. It is equipped with a bi-layer graphene membrane, acting as the working electrode, on top of a few-nanometer transition-metal oxide catalyst film – both transparent enough to electrons above 300 eV kinetic energy and to soft X-rays – that allows us to study the solid-liquid interface at a defined electrode potential using the Bessy II synchrotron soft X-ray source. Our method of choice is resonant PES, which displays details about the metal-water hybridization at the interface, by detecting the resonant Auger electron emission at the transition metal L-edge and water oxygen K-edge.

S.P.1
17:30
Authors : Mailis Lounasvuori, Tristan Petit
Affiliations : Helmholtz-Zentrum Berlin für Materialien und Energie, Institute for Nanospectroscopy, Albert-Einstein-Str. 15, 12489 Berlin, Germany

Resume : Electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) was first introduced by Osawa [1] and co-workers and has emerged as a powerful tool for probing electrified interfaces. Silicon is often the material of choice for the internal reflection element (IRE) due to its wide pH stability and its compatibility with various metal thin film deposition techniques. Because silicon suffers from inherent absorptions in the fingerprint region, the path length through the IRE becomes a critical parameter in achieving high throughput. A recent alternative to usual cm-sized IREs are the microstructured wafers reported by Schumacher et al. [2] and further developed by the Burgess group [3]. Grooves, formed by wet chemical etching of a 500 μm thick Si wafer, allow the use of the wafer as a single-reflection IRE. Due to the considerably shorter path length, the accessible wavelength window is wider compared to conventional Si IREs. Here we present an ATR-SEIRAS setup for investigations of the electrochemical double layer at Au thin film electrodes based on low-cost Si wafers. Two different microstructures with different groove angles are compared in terms of spectral intensity of potential-dependent operando SEIRA spectra, collected during electrochemical measurements in sulfate and bicarbonate electrolyte. [1] Bull. Chem. Soc. Jpn.1997, 70 (12), 2861-2880. [2] Appl. Spectrosc. 2010, 64, 1022−1027. [3] Anal. Chem. 2017, 89, 11818-11824.

S.P.2
17:30
Authors : Mais Ahmad, Hannes Raschke, Ravi Prakash, Esser Norbert, Roland Hergenröder
Affiliations : Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Bunsen-Kirchhoff-Straβe 11-44139, Dortmund, Germany Leibniz-Institut für Analytische Wissenschaften – ISAS – e.V., Schwarzschildstr. 8, 12489 Berlin, Germany

Resume : Gallium nitride (GaN) semiconductor has numerous featured physical and chemical properties that make it a promising candidate for use in biomolecular-based microelectronic devices and biosensors because of its natural living-cell biocompatibility and potentiality to convert biological information directly into electrical signal;however, evaluation and assessment of GaN surfaces performance in such devices can be achieved via studying the chemical structure. In this study, the chemical structure and morphology of undoped GaN(0001) surfaces on sapphire substrates were investigated for different treatment procedures and in dry/wet-water conditions using a variety of surface sensitive techniques.

S.P.3
17:30
Authors : Pip C. J. Clark, Marco Favaro, Michael J. Sear, Martin Johansson, Sven Maehl, Roel van de Krol, David E. Starr
Affiliations : Clark, Favaro, Sear, van de Krol, Starr: Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Solar Fuels, Hahn-Meitner-Platz 1, D-14109 Berlin, Germany; Sear, Johansoon: SPECS Surface Nano Analysis GmbH, 13355 Berlin, Germany

Resume : Until recently, most ambient pressure x-ray photoelectron spectroscopy (APXPS) experiments have focused on the study of solid-gas interfaces. The recent extension of APXPS measurements to above 30 mbar opens the possibility to study aqueous solutions at their room temperature equilibrium vapour pressures. In combination with tender X-ray (2-12 keV) photoemission spectroscopy, solid-liquid interfaces beneath liquid layers of several 10s of nms can be probed1. This technique can be used to study electrochemical interfaces ¬in situ and -operando, under light conditions and applied potentials. Additionally, the study of the surface region of liquids can be achieved with a droplet train – a continually refreshed, stable source of uniform droplets2. Because of their stability, droplet trains offer the possibility to study the kinetics of chemical reactions, and the nucleation and growth of nanoparticles in solution. We present the capabilities of a new APXPS endstation based at the BESSY II synchrotron, designed for studying solid-liquid, liquid-vapour, and liquid-liquid interfaces. It has two interchangeable modules: the first for solid-liquid interface experiments (commissioned) and the second for droplet train experiments (in development). SpAnTeX is equipped with the first Phoibos 150 NAP analyzer that can reach photoelectron kinetic energies of 10 keV. We show the attenuation of the photoemission signal upto pressures of 30 mbar for photoelectron kinetic energies up to 8 keV, and measurements at 10 keV in 25 mbar of N2 gas. The analyzer is also equipped with a 2D-delay line detector, allowing time-resolved photoemission measurements in ambient conditions. This permits observations of chemical kinetics over time ranges from nanoseconds to seconds and longer. The analyser can also be used in an imaging lens mode, with a lateral-spatial resolution in the 10s of microns, under ambient conditions. Possible applications for this include the study of patterned electrodes and determining spatial differences in droplet reactions. 1 M. Favaro, F. F. Abdi, E. J. Crumlin, Z. Liu, R. Van De Krol and D. E. Starr, Surfaces, 2019, 2, 78–99. 2 D. E. Starr, E. K. Wong, D. R. Worsnop, K. R. Wilson and H. Bluhm, Phys. Chem. Chem. Phys., 2008, 10, 3093–3098.

S.P.4
17:30
Authors : D. Ruano, J. Cored, V. Pérez-Dieste, P. Concepción
Affiliations : ALBA Synchrotron Light Source; Instituto de Tecnología Química, Universitat Politècnica de València - Consejo Superior de Investigaciones Científicas (UPV-CSIC) ;ALBA Synchrotron Light Source; Instituto de Tecnología Química, Universitat Politècnica de València - Consejo Superior de Investigaciones Científicas (UPV-CSIC)

Resume : H2-based energy has long been regarded as a promising alternative to conventional fuels. One of the efficient methods for H2 production (CO free) is low temperature methanol steam reforming (MSR). The catalysts most commonly used for this process are copper based catalysts due to their high activity and low CO production. In connection with the active species in Cu-based catalysts for MSR, there is still ambiguity about their nature1. Few studies have evaluated structural changes of the catalyst under working reactions, specifically those taking place in the initial stage of the reaction. In our study2, the dynamic behavior of a Cu65Zn25Ga10 catalyst under MSR reaction conditions was found by the application of temporal resolution catalytic studies and synchrotron near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS). Surface copper atoms remain in a metallic state while they are electronically perturbed by the presence of subsurface oxygen species. These species influence the catalytic behavior of the system in MSR, increasing its performance. The presence of these subsurface oxygen species is due to the fast oxidation and further reduction of the copper particle during the first minutes of the reaction, and results undetected using a conventional setup. Thus, the use of spatiotemporal resolved spectroscopies with in-situ capabilities (during reaction conditions) are needed to fully understand the catalytic behavior of a catalyst. 1 GS. Wu, DS. Mao, GZ. Lu, Y. Chao, KN. Fan. Catal. Lett. 2009, 130, 177-184. 2 D. Ruano, J. Cored, C. Azenha, V. Pérez-Dieste, A. Mendes, C. Mateos-Pedrero, P. Concepcion. ACS Catal. 2019, 9, 2922-2930.

S.P.5
17:30
Authors : E. Magnano, S. Nappini, F. Bondino, I. Píš
Affiliations : IOM-CNR, Laboratorio TASC, S.S. 14-km 163.5, 34149 Basovizza, Trieste, Italy Elettra-Sincrotrone Trieste S.C.p.A, S.S. 14-Km 163.5,34149 Basovizza, Trieste, Italy

Resume : The CNR Beamline for Advances Circular diCHroism (BACH) operating at Elettra in Trieste (Italy), works in the VUV-soft x-ray photon energy range with selectable light polarization, high energy resolution, brilliance and time resolution . The beamline offers a multi-technique approach for the investigation of the electronic, chemical, structural, magnetic and dynamical properties of materials. One of the three end-stations has been recently dedicated to experiments based on electron transfer processes at the solid/liquid interfaces during photocatalytic or electrochemical reactions. This goal has been pursued by the development and implementation of new strategies. The encapsulation of liquid solutions between a graphene layer and a solid substrate was successfully applied to the study of thermo and photo-induced reactions by X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). A second approach is the use of a microfluidic cell, consisting of a Si3N4 membrane which separates the liquid from the vacuum and equipped with a three electrodes systems, where the working electrode (WE) is the membrane itself. The electrochemical cell allows to carry out cyclic voltammetry in situ or electrochemical deposition on the WE and chemical reactions in-operando conditions. XAS in fluorescence is used for the operando characterization, providing unique information with elemental sensitivity of the chemically active atomic orbitals of the material. We plan to implement the use of hole array membranes covered by graphene layers in order to have access also to XPS. The availability of a fs laser synchronized with the x-ray beam will allow pump and probe XAS experiment in liquid environment in-operando conditions.

S.P.6
17:30
Authors : Dr. Laura C. Pardo-Perez, Sasho Stojkovikj, Alexander Arndt, Dr. Matthew T. Mayer
Affiliations : Nachwuchsgruppe Elektrochemische Umwandlung von CO2, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH

Resume : Electrochemical reduction of carbon dioxide can produce a wide variety of products with poor control over selectivity and poor efficiency. The nature of the catalyst surface plays a central role in dictating the reaction activity, and researchers are working to develop new catalysts and uncover design principles enabling selective and efficient production of a desired product. A key challenge is that electrocatalyst structure is highly dependent on the applied electrochemical potential and the chemical environment, especially under the particularly reducing conditions required for CO2 reduction. Methods for in situ study of electrodes under operating conditions are therefore crucial. In seeking to modify catalyst activity by surface functionalization, we discovered that sub-nm ALD coatings of SnO2 films onto CuO nanostructure electrodes led to huge changes in catalyst selectivity, converting CO2 to CO (carbon monoxide) with selectivity exceeding 90%. Since this behavior is atypical for either CuO or SnO2 electrodes themselves, a synergetic effect between the two components is likely. We employed X-ray spectroscopy to investigate the electronic states and chemical environments of Cu and Sn using soft and hard X-ray techniques at BESSY II. We discovered that, during electrochemical operation, the Sn migrates away from the surface and into the CuO bulk. The presence of Sn influences the observed oxidation state of Cu near the surface, which remains partially oxidized (in comparison to fully reduced Cu which is observed in the absence of Sn). This result shows that electrocatalytic surfaces can be significantly affected by the presence of trace sub-surface dopants, causing changes in electronic structure which affect catalytic mechanisms and the resulting product selectivity.

S.P.7
17:30
Authors : Peter Amann (1), David Degerman (1), Mikhail Shipilin (1), Patrick Loemker (2), Christoph Schlueter (2), Sara Blomberg (3), and Anders Nilsson (1)
Affiliations : (1) Department of Physics, Stockholm University, AlbaNova University Center, 10691 Stockholm, Sweden; (2) Photon Science, Deutsches Elektronen Synchrotron DESY, 22607 Hamburg, Germany; (3) Department of Physics, Lund University, Lund 221 00, Sweden

Resume : The chemical industry is one of the most important sectors of our economy and it is estimated that nearly 90% of all chemical products rely on suitable catalysts that enhance the rate of chemical reactions. In order to generate a sustainable society, hydrogenation processes related to CO and CO2 are of great importance to generate fuels. However, the related processes take place under elevated pressures of several bars and increased temperatures above 100°C. Some of the most important information about the catalytic process is related to the bond breaking and bond formation of molecules at interfaces. In order to gain insight into the mechanistic details, we have developed a new high-pressure x-ray photoelectron spectroscopy setup capable of acquiring spectra at pressures exceeding 1 bar and temperatures up to 500°C under operando conditions. The instrument takes advantage of a “virtual cell” which is a novel concept in which a gas stream is pointed towards the sample surface to create a localized high-pressure pillow. Synchrotron based hard x-ray excitation is used to enhance the inelastic mean free path of the electrons inside the high-pressure gas environment. We use grazing incidence spectroscopy for efficient detection of surface species, using a precision motion manipulator, capable of scanning the incidence angle with step sizes of 2urad. Details on the instrument and first measurement results obtained at beamline P22 at Petra III will be presented.

S.P.8
17:30
Authors : G. Agostini, D. Meira, M. Monte, H. Vitoux, A. Iglesias-Juez, M. Fernández-García, O. Mathon, F. Meunier, G. Berruyer, F. Perrin, S. Pasternak, T. Mairs, S. Pascarelli, B. Gorges
Affiliations : ERSF – European Synchrotron Radiation Facility, Grenoble (France); ALBA - Synchrotron, Cerdanyola del Valles (Spain); Instituto de Catálisis y Petroleoquimica (ICP-CSIC), Madrid; Institut de Recherches sur la Catalyse et l'Environnement de Lyon, Villeurbanne (France);

Resume : The combination of complementary techniques in the characterization of catalysts under working conditions is a very powerful tool for an accurate and in-depth comprehension of the system investigated. In particular, X-ray absorption spectroscopy (XAS) coupled with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and mass spectroscopy (MS) is a powerful combination. In the present contribution, a new reactor cell and an experimental setup are presented. The system stands out among others for its achievements and flexibility. The reactor cell is made up of the main body, where the heater and the reactive gas pipes are placed, sharing different domes can be placed. This solution allows to optimize the setup for different applications and future development with only minor adaptation. A key feature of this setup is the possibility to work at high temperature and pressure, with a small cell dead volume (up to ≤ 0.5 cm 3 ) to perform time-resolved experiments on heterogeneous catalysts under working conditions. XAS measurements can be performed in transmission or fluorescence modes, and the cell is compatible with external devices like UV-light and Raman probes. To demonstrate these capabilities, performance tests with and without X-rays are performed. The effective temperature at the sample surface, the speed to purge the gas volume inside the cell and catalytic activity have been evaluated to demonstrate the reliability and usefulness of the cell.

S.P.9
17:30
Authors : Luca Artiglia, Zbynek Novotny, Anthony Boucly, Nicoló Comini, Joerg Raabe, Thorsten Bartels-Rausch, Markus Ammann, Jeroen van Bokhoven, Juerg Osterwalder
Affiliations : Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland) and University of Zurich, Winterthurerstrasse 190, 8057 Zurich (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland); University of Zurich, Winterthurerstrasse 190, 8057 Zurich (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland); Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen (Switzerland) and ETH Zurich, Vladimir-Prelog-Weg 1/10, 8093 Zurich (Switzerland); University of Zurich, Winterthurerstrasse 190, 8057 Zurich (Switzerland).

Resume : Interfaces are the place where most of the chemical reactions occur, but are intrinsically difficult to investigate, because of their nano-confinement. Thanks to its surface sensitivity and to the possibility to investigate real samples in the millibar pressure range, x-ray photoelectron spectroscopy can be considered a promising technique. This poster will describe a new beamline at the Swiss light source synchrotron (Paul Scherrer Institute), where ambient pressure x-ray photoelectron spectroscopy and near edge x-ray absorption fine structure spectroscopy can be carried out to characterize in situ reactions at the solid-gas and at the solid-liquid interface. The solid-gas interface endstation allows the characterization of actual samples (powders) exposed to reactive gas environments. Thanks to the small volume of the analysis cell, pulsed experiments are possible, so that the electronic properties of samples can be tested under transient reaction conditions with a time resolution in the second range. Depending on the research topic, it is possible to control the sample temperature either in the high temperature range (room temperature to 650°C) or in the low temperature one (100°C to -100°C). This makes the setup particularly suitable for catalysis and environmental chemistry experiments. The solid-liquid interface chamber has just been commissioned. In this setup it is possible to stabilize a thin liquid film on top of a solid sample by a dip&pull method. Using tender X-rays, we can probe the solid-liquid interface collecting photoelectrons emitted from the buried interface. A customized three electrode system allows the precise control of the potential over the electrolyte film, making the setup suitable for electrochemistry experiments.

S.P.10
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Spectroscopy and Electrochemistry : Junko Yano
09:00
Authors : Ib Chorkendorff
Affiliations : Department of Physics, Technical University of Denmark (DTU) Fysikvej, Building 312, DK-2800 Kongens Lyngby, Denmark.

Resume : In situ methods are essential in getting insight into surface composition and structure under the dynamical reaction behavior. In this presentation shall we give example on how such methods as surface X-ray diffraction and EXAFS could be used to elucidate the surface behavior of a new class of electrocatalysts for the Oxygen Reduction Reaction (ORR). ORR is the limiting reaction in Proton Exchange Membrane Fuel Cells. Here we have found entirely new classes of electro-catalysts by alloying Pt with early transition metals [1] or the lanthanides [2]. We have shown that it is also possible to make mass-selected nanoparticles of these alloys with very good activities [3] and PtGd alloys [4] although direct translation of such results to fuel cells is difficult [5]. The same principles will be used to demonstrate investigation of conversion of CO or CO2 into valuable fuels and chemical electrocatalysis [6,7,8]. If time allows, we shall also discuss how these methods can be used to elucidate the state of the Ciu-Ru catalysts used for ammonia conversion to hydrogen [9]. References [1] J. Greeley,…. I. Chorkendorff, J. K. Nørskov, Nature Chemistry. 1 (2009) 522 [2] M. Escudero-Escribano, … I. E.L. Stephens, I. Chorkendorff, Science 352 (2016) 73. [3] P. Hernandez-Fernandez, , …, I. Chorkendorff, Nature Chemistry 6 (2014) 732. [4] A. Velázquez-Palenzuela…. I. Chorkendorff, J. Catal. 328 (2015) 297. [5] I. F. L. Stephens, J. Rossmeisl, I. Chorkendorff, Science 354 (2016) 1378. [6] E. Bertheussen, …I. Chorkendorff, Angewandte Chemie 55 (2016) 1450. [7] S. B. Scott,…. I. Chorkendorff ACS Energy Lett. 4 (2019) 803. [8] S. Scott, …. I. Chorkendorff. Submitted (2019). [9] D. Chakraborty, … I. Chorkendorff, Angewandte Chemie 56 (2017) 8711.

S.6.1
09:35
Authors : Moumita Rana, Venkata Sai Avvaru, Nicola Boaretto, Vinodkumar Etacheri and Juan Jose Vilatela
Affiliations : Multifunctional Nanocomposite Group IMDEA Materials Institute C/ Eric Kandel 2, Parque de Tecnogetafe 28906-Madrid, Spain

Resume : Transition metal oxides (TMO) are gaining increasing attention as next generation rechargeable lithium-ion battery anode due to their high theoretical capacity and electrochemical stability.[1,2] Among them, MnO2 is the most promising one due to its highest theoretical capacity and lower operational potential compared to other TMOs. Even though there are plenty of studies on exploring the electrochemical activity of nanostructured MnO2, their charge-discharge mechanism is not yet clear, and the information about the lithium storage mechanism of MnO2 is inadequate with respect to other TMO based materials.[3-5] In this work, we have developed a high performance MnO2@carbon nanotube (MnO2@CNT) hybrid anode for Li-ion battery. Detailed investigations using electrochemical, in-situ synchrotron X-ray scattering and Raman spectroscopy studies reveal that, during the first charge-discharge cycle, the material undergoes an irreversible phase transformation to a lithiated form of manganese oxide. In the consecutive cycles, this structure undergoes a reversible phase transformation with metallic manganese. Additionally, the high surface area of oxide nanostructures provides additional surface Li-storage sites, that leads to enhanced specific capacity, surpassing its theoretical value. This study provides a comprehensive understanding of possible Li-storage routes in nanostructured MnO2, and establishes a necessity to revisit the conventional concept of reversible lithium storage conversion mechanism in transition metal oxides. References 1. M. Zheng, H. Tang, L. Li, Q. Hu, L. Zhang, H. Xue, H. Pang, Advanced Science 2018, 5,1700592. 2. L. Shen, Q. Dong, G. Zhu, Z. Dai, Y. Zhang, W. Wang, X. Dong, Advanced Materials Interfaces 2018, 5, 1800362. 3. C. Chen, N. Ding, L. Wang, Y. Yu, I. Lieberwirth, Journal of Power Sources. 2009,189, 552. 4. X. Fang, X. Lu, X. Guo, Y. Mao, Y.-S. Hu, J. Wang, Z. Wang, F. Wu, H. Liu, L. Chen, Electrochemistry Communications 2010. 12, 1520. 5. A. A. Voskanyan, C. K. Ho, K. Y. Chan, Journal of Power Sources 2019, 421, 162.

S.6.2
09:55
Authors : Anthony Boucly(1), Emiliana Fabbri(1), Luca Artiglia(1), Xi Cheng(1), Daniele Pergolesi(1),Thomas Lippert(1), Markus Amman(1), Thomas J. Schmidt(1,2)
Affiliations : (1)Paul Scherrer Institut, Forschungsstrasse 111, CH−5232 Villigen PSI, Switzerland; (2)Laboratory of Physical Chemistry, ETH Zürich, CH−8093 Zürich, Switzerland

Resume : Perovskite oxides have emerged as promising anodic electrodes for the oxygen evolution reaction (OER) in alkaline water electrolyzers showing high mass current densities at relatively low overpotential and promising stability under operative conditions.[1,2] In particular the La1-xSrxCoO3 compositions in the “as prepared” form present strontium surface segregation and consequently Co depletion compared to the lattice stoichiometry. So far, the influence of surface segregation on the OER activity of perovskites as electrocatalysts has been poorly investigated. Here I present a study of the most active composition towards the OER in alkaline electrolyte among the La1-xSrxCoO3 series[3], the La0.2Sr0.8CoO3 perovskite, produced in the form of thin films by pulsed laser deposition (PLD) using different deposition temperatures. This study focus on determining the influence of the thin film growth temperature on the strontium segregated layer and its impact on the OER activity of the perovskite using XPS characterization Electrochemical measurement and microscopy. The main highlight of this study being that higher growth temperature translate to an increased activity towards the oxygen evolution reaction through an enhanced cobalt presence at the surface after the strontium segregated layer has been washed. [1]Kim, B. J. et al., Adv Funct Mater 2018, 28 (45) [2]Fabbri, E. et al., Nature Materials 2017, 16, 925–931 [3]Cheng, X. et al., Chemistry of Materials 2015, 27 (22), 7662-7672

S.6.3
10:30 Coffee Break    
 
Spectroscopy and Catalysis I : Anja Bieberle
11:00
Authors : Miguel A. Bañares 1, Qingyue Wang 1,2, Raquel Portela 1, Celina Barrios 3, Sebastián Collins 3, King L. Yeung 2
Affiliations : 1 Institute for Catalysis, CSIC, Madrid, SPAIN; 2 The Hong Kong University of Science and Technology, HONG KONG; 3 INTEC, CONICET, Santa Fe, ARGENTINA

Resume : Vanadium and gold have remarkably different impact on ceria performance for toluene oxidation. Au/CeO2 and CeO2 catalysts (T50 = 260 and 290oC) were more active and selective toward the complete oxidation of toluene than VOx/CeO2 catalyst (T50 = 370oC), where T50 refers to the temperature for 50% of CO2 yield. VOx/CeO2 produced significant amount of benzaldehyde as partial oxidation byproduct and CO (<25%). The nature of the active sites, configurational adsorption of toluene and the reactive oxygen species play important roles in the catalyst activity and selectivity leading to a large contrast in the catalytic behavior. Operando Raman and modulation excitation spectroscopy (MES) operando infrared studies bring complementary insights on the mechanistic aspects of toluene oxidation, the nature of the active site, catalyst state, adsorbed hydrocarbon and oxygen species. The CeO2, VOx/CeO2 and Au/CeO2 catalysts present different active sites for toluene adsorption and reaction, resulting in very different reaction behavior. Vanadium and gold have a reducing effect on ceria; this, in turn, stabilizes oxidized states for vanadium and gold, V5+ (99.0%) and Au+ (73.2%). Toluene molecule adsorbs with its aromatic ring parallel to the surface of CeO2 and Au/CeO2 catalysts via -bonding that appears to destabilize the aromatic ring resulting in a more rapid and complete oxidation to CO and H2O. Toluene is adsorbed as carbenium ion on Brønsted acid sites of 2.5V/CeO2 and produces benzaldehyde as the main partial oxidation byproduct. This work was supported by the Spanish Ministry [CTM2017-82335-R]; NSFC/RGC Joint Research Scheme [N-HKUST626/13]; European Commission Grant 814426 NanoInformaTIX and Guangzhou Collaborative Innovation Key Program [201704030074]. The authors express their gratitude to Dr. Laura Pascual, Dr. Wei Han, Ms. Mei Leng Liu, Mr. Hoi Yau Cheng and Mr. Nick K C Ho for technical supports. Also, thanks to the Oversea Research Award from School of Engineering, HKUST for supporting the exchange program at the ICP-CSIC, in Spain.

S.7.1
11:35
Authors : Angeles Lopez-Martin, Gerardo Colon, Alfonso Caballero
Affiliations : Instituto de Ciencia de Materiales de Sevilla (CSIC-University of Seville) and Departamento de Quimica Inorganica. University of Seville. Av. Americo Vespucio, 49; 41092 Seville, Spain

Resume : The reaction of direct aromatization of methane (DAM) has raised a great interest in the last years. This reaction, which could be a way to take advantage of the big amount of available natural gas, is mainly accomplished using molybdenum based material, the most performance catalytic system for this reaction. However, a number of characteristics are not well known until now, related both with the role of the support, mainly zeolite based solids and the kind of molybdenum active phases located in the microporous structure. It is widely accepted that, under reaction conditions a molybdenum carbide phase is formed, which transform the methane through a bifunctional mechanism in cooperation with the Bronsted acid site of the zeolite. Also, it has been previously found that different molybdenum precursors coexist in the catalysts, depending on features as the preparation methodology, the pretreatment or the aluminum content of the zeolite. We need to know all these features to stablish the role of each specific phase in the DAM reaction, including the presence of some inactive or spectators phases, or even phases that could hinder the catalytic performance of the system, for instance favoring the formation of coke species blocking the porous and the access to the active phase. In this work, we have synthesized by impregnation several Mo/ZSM-5 catalysts with metal contents ranging from 1 to 10 wt%. After a calcination treatment at 550ºC, its catalytic performance in the DAM reaction were evaluated, and finally characterized by several techniques, in particular in situ XPS and TPR. These two complementary techniques have allowed us to look into the physical and chemical state of the different molybdenum phases supported on the ZSM-5 zeolite.

S.7.2
11:55
Authors : C. Hartwig, K. Schweinar, S. Beeg, M. Greiner, R. Schlögl
Affiliations : Max-Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, Mülheim an der Ruhr, Germany; Max-Planck Institute for Iron Research, Düsseldorf, Germany; Fritz Haber Institute of the Max-Planck Society, Berlin, Germany

Resume : Catalytic properties can be tuned by alloying, due to changes in the catalyst’s geometry and electronic structure. Single-atom alloys consist of active metal atoms distributed in the matrix of another metal, in a way that there are no bonds between neighboring active sites. Such an approach has the ability to combine the advantages of heterogeneous and homogeneous catalysis, since it can lead to a narrowing of the active metals d-states. Recently our group discovered by XPS analysis that Ag99.5%Cu0.5% single-atom alloys exhibit a unique free atom electronic structure, where the Cu 3d band is separated from the Ag 4d band. The Cu 3d band in the alloy is surprisingly narrow, with a width of 0.5 eV, compared to 2.5 eV in bulk Cu. The effect this narrow d-band might have on adsorbate bonding and catalysis, was predicted and demonstrated for one case study of methanol reforming (Greiner et al. Nat. Chem. 10, 1008–1015 (2018)). In our current research we are investigating the single-atom electronic structure in AgPd alloys, dilute in Pd. For this project AgPd alloy foils with variable amounts of Pd were synthesized, and analyzed using in situ NAP-XPS at BElCHem beamline (BESSY II). It was found that the Pd 4d valence band is separated from the Ag 4d states, and is narrowed in the alloy compared to bulk Pd. Additionally, the oxidation properties of Pd in AgPd were found to be different from bulk Pd, indicating an effect on the chemical reactivity of Pd atoms in AgPd single-atom alloys.

S.7.3
12:15 Lunch Break    
 
Spectroscopy and Catalysis II : Miguel Banares
14:00
Authors : Olga V. Safonova
Affiliations : Paul Scherrer Institute, 5232 Villigen PSI, Switzerland

Resume : Detection of true reaction intermediates in heterogeneous catalysis is challenging due to heterogeneity of catalytic surfaces, low concentration of active species, short lifetime of intermediates, and insufficient sensitivity of spectroscopic methods. We developed highly sensitive time-resolved X-ray absorption spectroscopy methods allowing quantitative assessment the redox activity of various metal centers in the catalytic oxidation reactions. This approach helped us to observe the full complexity of low temperature CO oxidation mechanisms on ceria-based catalysts. The most interesting results are the following: i) Active and spectator Ce3+ species co-exist in Pt/CeO2, Pt/Ce0.5Zr0.5O2 and Pt/Ce0.5Sn0.5O2 catalysts under working conditions of low-temperature CO oxidation but can be distinguished under transient conditions. ii) The Ce3+ formation rate at the metal-support interface is involved in the rate-determining step of low temperature CO oxidation over Pt/CeO2 and Pt/Ce0.5Zr0.5O2 catalysts. Higher activity Pt/Ce0.5Sn0.5O2 catalysts at low temperatures is related to the acceleration of Ce3+ formation rate, which becomes faster than the Ce3+ oxidation rate changing the rate-determining step. iii) For Cu-promoted ceria, the CO oxidation rate at low temperatures correlates to the reduction Cu2+ to Cu+. The Ce3+ formation rate is significantly slower but has similar kinetic trend and activation energy, suggesting that activation of oxygen takes place on an ensemble of Cu and Ce atoms. The described spectroscopic methods have high potential for mechanistic studies of various oxidation catalysts.

S.8.1
14:20
Authors : Fernando García-Martinez(1), Iradwinaraki Waluyo(2), Andrew Walter(2), Adrian Hunt(2), Frederik M. Schiller(1), and J. Enrique Ortega(1,3,4)
Affiliations : 1-Centro de Física de Materiales CSIC, San Sebastian (Spain); 2-National Synchrotron Light Source II, Brookhaven National Lab (USA); 3-Departamento Física Aplicada I, Universidad del País Vasco, 20018-San Sebastian (Spain); 4-Donostia International Physics Center DIPC, 20018-San Sebastian (Spain);

Resume : The study of the catalytic oxidation of CO on Pt single crystals and nanoparticles has been a wide research field since long. However, the role and the interplay among different coordination sites and facet planes remain unclear. This is in part because both crystal surfaces and nanoparticles undergo complex structural/chemical changes during catalytic reactions. In this context, using multi-facet samples, such as cylindrical crystals, for in-situ studies is highly desirable [1,2]. We have carried out near-ambient pressure X-ray photoemission (NAP-XPS) experiments of the CO oxidation using a curved Pt(111) crystal [c-Pt(111)] that exposes vicinal surfaces with a smoothly varying density of A-type and B-type close-packed steps. The NAP-XPS spectra are compared with room-temperature chemisorption experiments of CO and O2 carried out in Ultra-High-Vacuum, allowing us to identify and quantify surface chemical phases for each vicinal plane, before and after its catalytic activation, and under different reaction conditions. When exposing the c-Pt(111) surface to constant millibar pressures of nearly stoichiometric mixtures of CO and O2, we find that the catalytic activation process occurs in two different steps. During a slow, stepwise increase of the surface temperature, we observe the transition from the low-activity poisoned stage, defined by a mixture of chemisorbed CO and graphitic C, to a transient state, characterized by a complete removal of graphitic C, a lower, but sizeable, concentration of chemisorbed CO, and the emergence of an oxygen-related species of unknown nature. Such transient state already exhibits a very high activity (CO2 production) and extends another 20-50 K, before the abrupt transition to the canonical, highest activity stage, where the surface appears free of carbon-related species (minor amounts at densely-stepped B-type vicinals), and covered only with Pt oxides and chemisorbed oxygen. Such two-step transition is reversible, showing no hysteresis during the cooling-off process. The direct comparison with UHV spectra at 300 K serves to quantitatively determine the composition of the surface chemical phases across the curved surface at each reaction stage. CO cracking and build-up of graphitic carbon in the poisoned stage is more efficient at the stepped sides of the crystal, whereas the amount of chemisorbed CO during the poisoned and the transient stages at (111) terraces is lower than in UHV. In the most-active, oxygen-related phase Pt oxides grow thicker at densely-stepped surfaces, whereas a clear A/B asymmetry is found for step-chemisorbed O atoms. Despite the differences in surface chemical phases, the two-step catalytic activation of Pt occurs at the very same temperature at all vicinal orientations. Although the reaction conditions (pressure, ratio of reactants, heating rate) modify transition temperatures and proportions of surface chemical phases (graphitic C versus CO, chemisorbed oxygen versus oxides), the simultaneous character of the activation process at all crystal planes remains unaltered. Such behavior is corroborated by fluorescence experiments carried out under rather different flux/pressure conditions, and strongly contrasts with the sequential ignition observed in the analogous c-Pd(111) surface, where B-type vicinals ignite first, followed by A-type steps, and the high symmetry (111) plane [2]. This surprising behavior, as well as the microscopic nature of the transient state, is being investigated by density-functional calculations. Bibliography [1] A. L. Walter et al. Nat Comm 6, 8903 (2015). [2] F. Schiller et al., J. Am. Chem. Soc., 140, 16245−16252 (2018). Acknowledgments We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT-2016-78293-C6, MAT-2017-88374-P) and Basque Government (Grant IT-1255-19).

S.8.2
14:40
Authors : Xiansheng Li1,2, Luca Artiglia*1, Jeroen A. van Bokhoven*1,2
Affiliations : 1Paul Scherrer Institute, CH-5232 Villigen, Switzerland 2Institute for Chemical and Bioengineering, ETH Zurich, CH-8093 Zurich, Switzerland

Resume : In situ ambient X-ray photoelectron spectroscopy (AP-XPS) was used to elucidate the active sites and mechanistic steps associated with the CO oxidation reaction over high temperature steam-treated Pt/CeO2 catalysts. Our results suggest that cationic Pt2+ is the exclusive active site on the “as synthesized” Pt/CeO2 catalyst while metallic Pt0 sites, which are the likely active species for the higher CO oxidation activity, are detected after steam treatment. The ceria support has an active role in the reaction, displaying reversible reduction-oxidation behavior under different reaction conditions. We introduced in situ time-resolved measurements to quantitatively follow the fraction of Ce3+ and Ce4+ as a function of the reaction temperature and gas environment. The kinetic rates of ceria oxidation and determine the ceria reduction degree under reaction conditions and their role in the reaction mechanism are established.

S.8.3
15:00
Authors : Sara Blomberg, Hanna Karlsson, Christian Hulteberg, Johan Gustafson, Uta Hejral, Stefano Albertin, Edvin Lundgren, Peter Amann, Mikhail Shipilin, David Degerman, Anders Nilsson, Patrick Lömker, Christoph Schlueter
Affiliations : Dept. Chemical Engineering Lund University; Dept. Physics Lund University; Dept. Physics Stockholm University; Photon Science DESY

Resume : CO oxidation is a well-known reaction that has been studied for several decades. To achieve a fundamental understanding of the reaction, model systems are often used and the reaction is, traditionally, studied at well-controlled conditions at low pressures. This is in contrast to the industrial catalyst, which is operating at atmospheric pressure and above. It has been an ongoing debate if the results achieved at low pressures are relevant also for industrial conditions, often referred to as the pressure gap. Over the last decades, a great effort has been made to develop electron based-surface sensitive techniques to operate at more realistic conditions, but it is not until recently XPS experiments at 1 bar has become possible with a new XPS setup, POLARIS, at beamline P22, DESY, Hamburg. Herein, we report on the first CO oxidation experiment on Pd(100) that has been performed at a total pressure of 1 bar using XPS. The results are achieved operando where we can follow the chemical composition of the surface going from an inactive CO poisoned surface to a highly active Pd(100) where the detected gas phase peaks, originating from CO as well as the CO2, are a clear indication of the activity of the Pd(100) surface. In an attempt to close the pressure gap a systematic study was also performed where the light-off temperature and oxygen coverage of the Pd(100) as a function of the total pressure, ranging from 10 mbar up to 1 bar, was measured.

S.8.4
15:30 Coffee Break    
 
Spectroscopy and Catalysis III : Peter Amann
16:00
Authors : L. Lindenthal, R. Rameshan, J. Popovic, T. Ruh, J. Raschhofer, A. Nenning, A.K. Opitz, C. Rameshan
Affiliations : L. Lindenthal, R. Rameshan, J. Popovic, T. Ruh, J. Raschhofer, C. Rameshan, all Institute of Materials Chemistry, TU Wien, Austria; A. Nenning, A.K. Opitz, Institute of Chemical Technologies and Analytics, TU Wien, Austria

Resume : In heterogeneous catalysis surfaces decorated with uniformly dispersed, catalytically highly active (nano)particles are a key requirement for excellent performance. Beside the standard catalyst preparation routines, with limitations in terms of controlling exactly the desired catalyst structure (i.e. particle size or dispersion), we present here an innovative, time efficient route to exactly tailor the catalyst surface directly during reaction (scope of my ERC project). Perovskite-type catalysts can incorporate catalytically highly active guest elements as dopants. When applying reductive conditions these dopants emerge from the oxide lattice to form catalytically active nanoparticles on the surface (by exsolution), causing a strong enhancement of catalytic reactivity. For the newly synthesized perovskite materials (with Ni or Co doping), we show by in-situ spectroscopy (NAP-XPS, in-situ XRD) the formation of catalytically active nanoparticles on the surface. For reverse water gas shift reaction (rWGS) we revealed that these nanoparticles are strongly enhancing the activity. From all tested materials, cobalt doped perovskites showed the highest activity, making this catalyst highly promising for the utilization of CO2 and its transformation into synthesis gas. Acknowledgement This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° 755744 / ERC - Starting Grant TUCAS)

S.9.1
16:20
Authors : Jordi Fraxedas(1), Borja Sepúlveda(1), María José Esplandiu(1), Xènia García de Andrés (2), Jordi Llorca(2), Virginia Pérez-Dieste(3), Carlos Escudero(3)
Affiliations : (1) Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and BIST, Campus UAB, Bellaterra, Barcelona, 08193, Spain; (2) Institute of Energy Technologies, Department of Chemical Engineering and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, EEBE, Eduard Maristany 10-14, Barcelona, 08019, Spain; (3) Alba Synchrotron Light Source, Carrer de la Llum 2-26, Cerdanyola del Vallès, Barcelona, 08290, Spain

Resume : We have shown by means of Near-Ambient Pressure X-ray Photoemission Spectroscopy (NAP-XPS) experiments, performed at the NAPP branch of the CIRCE beamline from the ALBA Synchrotron Light Source, that ex situ activated platinum films (50 nm thick, grown on a silicon wafer and prepared under oxygen plasma conditions) become reduced by the combined effect of an intense soft X-ray photon beam and condensed water. The reduction processes mimics the inverse two-step mechanisms found in electro-oxidation of platinum; the surface oxidized platinum species become reduced first and then the adsorbed species desorb in a second stage leading to a surface dominated by metallic platinum. The reduction rate is lowered both when the condensed water amount and the photon flux are decreased and the exposure of the metallic surface to condensed water does not lead to oxidation. Such experimental evidences strongly suggest that the observed reduction is mainly induced by the reactive species generated through the radiolysis of water.

S.9.2
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09:00 Plenary Session (Main Hall)    
12:30 Lunch Break    
 
In-situ and Operando vibrational spectroscopies I : Philipp Stadler
14:00
Authors : Aafke C. Bronneberg, Richard van de Sanden, and Anja Bieberle-Hütter
Affiliations : Dutch Institute for Fundamental Energy Research (DIFFER), Eindhoven, 5612AJ, The Netherlands

Resume : Photon stimulated processes for water splitting are promising routes for building a sustainable energy society. However, the performance and efficiency are currently still too low. One main reason is that the mechanisms and related limitations at the interface are not well understood. At DIFFER, we approach this knowledge gap by a new combined approach of experimental studies and modeling. In this presentation, we focus mainly on the experimental side of the approach and report on a novel way to study the surface intermediates using operando ATR-FTIR spectroscopy (attenuated total reflection Fourier-transform infrared spectroscopy). We use the ZnSe internal reflection element (IRE) as substrate for the photoelectrode which has several advantages over geometries in which a thin electrolyte layer separates the photoelectrode from the IRE [1,2]. Using Fe2O3 as case study material, we will demonstrate the working principle of this approach and the feasibility of carrying out operando measurements. We will discuss the impact of applied potential, soaking time, and electrolyte on the FTIR spectra and will identify the intermediate surface species by fitting and comparison to relevant literature and predictions from simulations [3,4]. [1] Zandi et al. Nat. Chem. (2016). [2] Zhang et al. J. Am. Chem. Soc. (2018). [3] Zhang, Bieberle-Hütter et al. J. Phys. Chem. C (2016). [4] George, Bieberle-Hütter et al. J. Phys. Chem. C (2019).

S.10.1
14:35
Authors : Houcem elmaaoui
Affiliations : Universite de Caen

Resume : BIo-Corrosion products of carbon steel in a sea water in the presence of sulfate reducing bacteria (SRB) were investigated by in situ Raman spectroscopy with a self-designed device. The results of Raman analysis of samples in different immersion times indicate that the corrosion products on the surface of the carbon steel .The biofilm, mainly composed of extracellular polymeric substances, Fe(OH)3, γ-FeOOH andα-Fe2O3, formed and degraded with the SRB growth. The soluble iron concentration initially increased, then rapidly decreased and later slowly increased. In the SRB-containing seawater under the aerobic environment, the carbon steel was corroded in the initial immersion. The corrosion became inhibited with the forming of the biofilm during the subsequent immersion. The inhibition efficiency rapidly increased in the logarithmic phase, remained stable in the stationary phase and then decreased in the declination phase. In the corrosion process, the biofilm metabolized by SRB played a key role in the corrosion inhibition of carbon steel

S.10.2
14:55
Authors : Simone Rogg, Patrick Ober, Marcel Heber, Christian Hess
Affiliations : Eduard-Zintl Institute of Inorganic and Physical Chemistry, TU Darmstadt, Germany

Resume : The knowledge-based design of better catalysts and electrochemical devices is largely facilitated by the development and application of operando spectroscopic methods enabling the monitoring of the interface under working conditions. In this presentation, the potential of operando multi-wavelength Raman spectroscopy combined with operando UV-Vis spectroscopy will be highlighted. Regarding heterogeneous catalysts, combined operando multi-wavelength Raman / UV-Vis spectroscopy is applied to the oxidative dehydrogenation (ODH) of ethanol over silica- and ceria-supported vanadia catalysts. Using multiple excitation wavelengths in the UV and visible (256, 385, 514 nm), the resonance Raman effect is exploited in a targeted manner allowing to unravel the structural dynamics of both the vanadia and the support-related features. Our results provide new insight into the role of the support material in ODH reactions. Regarding electrochemical applications we will briefly demonstrate that multi-wavelength Raman analysis is also a valuable tool to gain insight into the structure of electrode materials used in Li-ion batteries such as layered Li-Ni-Mn-Co oxides (NMC). Our studies underline that detailed spectroscopic analysis is essential to elucidate the structure and structural dynamics of catalysts and electrochemical systems.

S.10.3
15:15 Coffee Break    
16:20
Authors : Sreetosh Goswami, T. Venkatesan
Affiliations : National University of Singapore, National University of Singapore

Resume : One of the long-standing challenges in organic memristors is to probe the molecular mechanisms. While there are hundreds of existing reports on molecular memory devices, none of the proposed mechanisms are understood. The propositions are hypothetical and unverified as a result of which these reports do not lead to any design principle which is one of the primary benefits of organic electronics in general. In this presentation, I will show that using in-situ Raman and spectroelectrochemistry we can deterministically conclude a redox-based switching mechanism in our molecular device that enabled us to engineer our device and the molecules to achieve the following: (i) Designing devices with ultra-low power: We are able to design memristors with switching voltage as low as 70mV, with energy ~36aJ/ 60nm^2. The current and voltage levels of these devices meet the requirements specified in the ITRS road map. (ii) Designing memristors and memcapacitors with multiple discrete plateaus: We have developed memristors with 3- 4 distinct conducting plateaus which also shows mem-capacitance. Their concomitant occurrence is enabled by symmetry breaking of our film-molecules driven by voltage, a new paradigm in condensed matter physics. (iii) Brain-inspired computing: Using an unprecedented self-assembly of our molecular films we are able to realize discrete conductance plateaus in a memristor with sharp switching. We are able to demonstrate up to 29 well defined, reproducible, discrete states each of which are characterized by in-situ Raman. We are exploring the potential of this system to enable synaptic functionalities. Also using the knowledge derived from the in-situ studies, we are unable to tune memristive states from continuum to discrete, from volatile to non-volatile. This can lead to a target specific device design strategy to serve analog as well as digital electronic platforms. References 1. Goswami S, Matula AJ, Rath SP, Hedström S, Saha S, Annamalai M, et al. Robust resistive memory devices using solution-processable metal-coordinated azo aromatics. Nature materials 2017, 16(12): 1216. 2. Valov I, Kozicki M. Non-volatile memories: Organic memristors come of age. Nature materials 2017, 16(12): 1170.

S.11.2
18:00 Graduate Student Awards Ceremony & Reception 18:00-21:00 (Main Hall)    

No abstract for this day


Symposium organizers
Luca ARTIGLIAPaul Scherrer Institute

Forschungsstrasse 111, 5232 Villigen PSI, Switzerland

luca.artiglia@psi.ch
Marco FAVAROHelmholtz-Zentrum Berlin für Materialien und Energie GmbH

Institute for Solar Fuels, Hahn-Meitner-Platz 1, 14109 Berlin, Germany

marco.favaro@helmholtz- berlin.de
Virginia PÉREZ-DIESTEALBA Synchrotron Light Source

Carrer de la Llum, 2-26, 08290, Cerdanyola del Vallès, Barcelona, Spain

vperezdieste@cells.es