Scope
The solid-liquid/gas interface is the region where electrochemical reactions and charge transfer take place, in particular in batteries, fuel cells, photo-electrochemical cells, and supercapacitors.
The functionality of electrodes depends on their interaction with their immediate environment such as gases and liquids, and temperature. In addition, the subsurface, charge carrier accumulation and depletion layers, diffusion layers and bulk regions are important for electrodes.
Their electronic structure depends on the synthesis and processing of materials and determines to a large extent the electronic and ionic transport properties of the electrodes. X-ray and electron spectroscopy methods are particularly well suited for the study of the electronic structure of such materials.
Soft X-ray spectroscopy is best suited for detection of electronic structure information, but it is challenging to carry out in-situ and operando electrochemical experiments. Yet, great progress has been made recently for example with ambient pressure XPS and liquid-cell soft X-ray absorption and emission spectroscopy. We are right now witnessing the beginning of a new era of operando X-ray and electron spectroscopy on energy storage and conversion devices.
Targeted Audience
Scientists and researchers, engineers who 1) have interest in the molecular structure-property-functionality relationship of electrode and electrolyte materials in batteries, fuel cells, photoelectrochemical cells, supercapacitors and their in-situ/operando assessment with x-ray spectroscopy, 2) are synchrotron staff and interested in electrochemical energy storage and conversion experiments.
Aim of the Workshop
This was 3 days of workshop with lectures, discussion rounds, round table work and one field excursion to the Swiss Light Source.
We brought together experts from electrochemistry, power sources, spectroscopy and synchrotron beamline engineering in order to explore the feasibility and limits of top-notch electrochemical operando analyses at synchrotron beamlines. The science was not limited to materials, but extended also to the components and even to the device level in operation. This naturally required very advanced in situ and operando methods.
Experts on batteries, fuel cells, supercaps and PEC cells gave their state of the art perception of the energy materials and devices landscape; and synchrotron and spectroscopy experts added their account on the current status and future view on the development of the field.
1. Summary
Empa, in collaboration with the Swiss Light Source, organised an “International Exploratory Workshop on Soft X-rays, Electrochemistry, and Energy Materials”. The workshop aided the assessment for a future dedicated experimental end station for the in-situ analysis and diagnostics of batteries, solar cells, fuel cells, supercapacitors and photoelectrochemical cells at the Swiss Light Source, extending from the materials to the components and the device level.
30 Participants and speakers from 12 countries delivered presentations ranging from x-ray scattering, catalysis and photoelectrochemistry to thermodynamics and “learning -from-nature”.
We have published the outcome of the recent 2013 SNF/Empa/PSI workshop in a synchrotron specific journal [A. Beni, A. Braun, T. Huthwelker, J. A. van Bokhoven, Meeting Report: Exploratory Workshop on Soft X-rays and Electrochemical Energy Storage and Converters, Synchrotron Radiation News 2013, 26 (5), 36-38].
2. Scientific aspects
2.1 Introduction of the research subject
The solid-liquid interface is an important region where electrochemical reactions and charge transfer take place. Several classes of electrochemical energy storage and conversion systems depend critically on the functionality of the solid-liquid (electrode-electrolyte) interface, in particular batteries, fuel cells, supercapacitors, and photo-electrochemical cells.
The functionality of electrodes depends not only on the electrode materials, but also on their interaction with their immediate environment such as fluids (gases and liquids) and temperature. In addition, not only the surface, but also the subsurface, depletion layers and diffusion layers and bulk regions are important for electrodes.
The electronic structure determines to a large extent the electronic and ionic transport properties of the electrodes. X-ray and electron spectroscopy methods are perticularly well suited for the study of the electronic structure of materials.
For example, heterogeneous catalysis is an energy related field that has greatly benefitted from synchrotron-based electron and X-ray spectroscopy with XPS and hard X-ray absorption spectroscopy. Similar holds for battery studies and to a lesser extent also fuel cell studies. Catalysis studies with XPS are by default done in ultra high vacuum. XAS studies typically are restricted to determination of the oxidation state of metal ions and to EXAFS oscillations. The hard X-rays allow for electrochemical in-situ studies, but are typically restricted to the two latter issues.
Soft X-ray spectroscopy is better suited for detection of electronic structure information, but it is difficult to carry out in-situ and operando electrochemical experiments. Yet, great progress has been made recently with ambient pressure XPS and liquid-cell soft X-ray absorption and emission spectroscopy particularly in Berlin and in Berkeley. We are right now witnessing the begin of a new era of operando X-ray and electron spectroscopy on energy storage and conversion devices.
Empa researchers have recently succeeded in making first-time ever, pioneering operando experiments at the Swiss Light Source (sulfur chemistry on SOFC anodes under electrochemical polarization at high T and H2S gas pressure), the Advanced Light Source (observation of solar photoelectrochemical water splitting by two new discovered electron holes in the valence band in the depletion layer of a hematite photoanode), and in Stanford the Mn L-edge bulk sensitive (!) spectral signature variation in a LiMn2O4 spinel cathode during charging and discharging of a lithium ion battery cell; monitoring of charge transfer in perovskite proton conductors during electrochemical polarization under high water vapor pressure using ambient pressure XPS).
2.2 Scientific aims and methods of the workshop
Experts from electrochemistry, power sources, spectroscopy and synchrotron beamline engineering will meet and explore the feasibility and limits of top-notch electrochemical operando analyses at synchrotron beamlines.
This is 3 days of workshop plus poster sessions plus discussion rounds and round table work.
Experts on batteries, fuel cells, supercaps and PEC cells will give their state of the art perception of the energy materials and devices landscape; and synchrotron and spectroscopy experts will add their account on the current status and future view on the development of the field.
2.3 Expected results
This Workshop is a „Begleitmassnahme“ for the planning of a future energy research dedicated soft x-ray beamline at the Swiss Light Source. There may be a follow-up workshop 2 years later.
3. Organisational aspects
3.1 Workshop Programme
Topics include: catalysis, electrocatalysis, photoelectrochemistry, x-ray/electron spectroscopy, nanoparticles, and molecular catalysts, lessons about electrode materials from the perspective of geochemistry and bio-electric interfaces.
Milestone will be a concluding remark by a workshop panel about the feasibility, suitability and limitations and potentials of ambient and near ambient pressure x-ray and electron spectroscopy for model systems and real-life systems and their functional assessment with combined chemical reaction engineering and electrochemical or electroanalytical assessment under operando conditions. This will be input information for the acquisition of a dedicated NAP-XPS instrument at Empa and/or at PSI SLS.
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3.2 Venue
The workshop took take place at Empa Akademie in Dübendorf, located right between the City of Zürich and Zürich International Airport, in close proximity to the Swiss Light Source in Villigen's Paul Scherrer Institut. International participants can travel with ease to Dübendorf from the airport by using the tram.
3.3 Funding
Funding: Swiss National Science Foundation Grant # IZ32Z0-147413, Swiss South African Joint Research Project # IZLSZ2-149031, Swiss Federal Office of Energy no° SI/501276-01, and by Empa.
4. Partnership aspects
4.1 List of participants
The workshop will take plate at Empa from 3-5 June 2013, with an excursion to SLS at PSI Villigen on 5 June.
4.2 Complementarity aspects
We bring together internationally renowned experts from electrochemistry (fuel cells, photoelectrochemical cells, solar cells), X-ray and electron spectroscopy (XPS, NEXAFS, PES, valence band spectroscopy), synchrotron beamline operation (ALS, SSRL, SLS).
This workshop narrows down the scope of the previous workshop from 2013 in terms of analytical approach and in terms of application and device technology. Specifically, we focus on catalysis and electrocatalysis for solar fuel generation. The method of choice is x-ray spectroscopy applied operando and in situ at the solid-gas or solid-liquid interface. We have experts from analytical methodology and experts from materials science and device technology, and thus cover a wide range including basic science and application and technology.
We have a broad group of participants that cover similar levels in the intermediate age range. During the workshop, PhD students will attend, as well as postdoc level scientists in order to learn from the excellent diverse and multi-facetted expertise present at the workshop.
We have researchers who work on materials aspects, analytical methods aspects, function of components aspects, compatibility of electroanalytical and x-ray spectroscopy methods and their application in realistic operando studies.
