Bentzen, Janet Jonna

Thydén, Karl Tor Sune

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Nov 09, 2017Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning ElectronMicroscopyBentzen, Janet Jonna; Thydén, Karl Tor SunePublication date:2016Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Bentzen, J. J., & Thydén, K. T. S. (2016). Tracking Electronic Pathways in Energy Materials by Low VoltageScanning Electron Microscopy. Poster session presented at SCANDEM 2016, Trondheim, Norway.Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning Electron Microscopy Acknowledgements: The authors like to thank for the financial support by Towards Solid Oxide Electrolysis Plants in 2020 (ForskEL 2015-1-12276).  * Corresponding author: Janet J. Bentzen, jabe@dtu.dk References 1. K. Thydén, Y.L. Liu and J.B. Bilde-Sørensen, Solid State Ionics 178, 1984–1989 (2008) 2. D.C. Joy, Compiled experimental electron scattering data http://www.mc-set.com/science/eesd/lb_load.php  Introduction Electrodes for energy conversion devices such as solid oxide fuel cells (SOFC) and electrolysis cells (SOEC) commonly consist of mixtures of electronically and ionically conducting ceramic and metallic materials in order to transport electrons and facilitate charge transfer to/from the electrolyte. For optimal performance it is paramount that the electronically conducting phases are well interconnected throughout the electrodes to create the required electronic connection from the electrolyte to the external circuit. Applying low voltage scanning electron microscopy and surface potential contrast [1] the interconnected electronic pathways within the electrodes can be tracked and evaluated. We here present examples of visualization of electronically percolating phases in electrodes for SOFC, SOEC, and devices for electrochemical reduction of NOx from exhaust gas from vehicles.  Experimental  Results and discussion Principle of a solid oxide electrolyzer cell (SOEC), and illustration of the tracking of the electronic pathways in both electrodes . Janet J. Bentzen and Karl T. S. Thydén  Department of Energy Conversion and Storage, Technical University of Denmark – Risø Campus SE2 and InLens images revealing the electronic pathways.  Microscope Stage /Ground  Electron source A schematic drawing illustrating the percolation contrast mechanism. Secondary electron coefficient for Ni as a function of acceleration voltage.  The microstructural investigations were performed using FEGSEMs Zeiss Supra 35 and Zeiss Merlin applying acceleration voltages in the range 0.9 kV to 1.3 kV. Many materials have a secondary emission coefficient σ higher than 1 in the low voltage range [2]. This is illustrated in the case of Ni in the schematic drawing  below. The in-lens secondary detector in a Zeiss Supra 35 microscope mainly picks up the part of the secondary signal that is produced directly by the primary electrons (the SE1 signal); e.g. an in-lens image of an SOFC Ni electrode at 1 kV will therefore show the percolating Ni with an emission coefficient around 1.3 provided that the sample is electrically connected to the stage. Contrary to this, the non-percolating Ni and the YSZ will charge until the barrier for secondary emission is so high that the sum of the backscatter coefficient and σ is 1. They will in other words be imaged with a secondary emission coefficient around 0.7. Visualization of the degradation of the contact between the Ni/YSZ electrode and the YSZ electrolyte in a solid oxide electrolyzer cell. Left image: Reference. Right image: After more than 4000 h of electrolysis. Visualization of electronically percolating phases in electrodes for devices consisting of LSCM/CGO for electrochemical reduction of NOx from exhaust gas from vehicles.  InLens SE2 InLens 

Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning Electron Microscopy

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Nov 09, 2017Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning ElectronMicroscopyBentzen, Janet Jonna; Thydén, Karl Tor SunePublication date:2016Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Bentzen, J. J., & Thydén, K. T. S. (2016). Tracking Electronic Pathways in Energy Materials by Low VoltageScanning Electron Microscopy. Abstract from SCANDEM 2016, Trondheim, Norway.Session: Materials science – Functional Materials SCANDEM 2016, Trondheim, Norway Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning Electron Microscopy Janet J. Bentzen*1 and Karl T. S. Thydén1  1 Department of Energy Conversion and Storage, Technical University of Denmark, Risø Campus, Frederiksborgvej 399, 4000 Roskilde, Denmark  *E-mail: jabe@dtu.dk  Keywords: electronic pathways, surface potential contrast, low voltage SEM, solid oxide cells, energy materials.  Electrodes for energy conversion devices such as solid oxide fuel cells (SOFC) and electrolysis cells (SOEC) commonly consist of mixtures of electronically and ionically conducting ceramic and metallic materials in order to transport electrons and facilitate charge transfer to/from the electrolyte. For optimal performance it is paramount that the electronically conducting phases are well interconnected throughout the electrodes to create the required electronic connection from the electrolyte to the external circuit. Applying low voltage scanning electron microscopy and surface potential contrast [1] (Fig. 1a) the interconnected electronic pathways within the electrodes can be tracked (Fig. 1b) and evaluated. Examples of evaluation of microstructures resulting from different processing and performance degradation phenomena will be presented.         a      b     Figure 1: a) Secondary electron coefficient for Ni as a function of acceleration voltage illustrating the contrast mechanism; b) Example of tracking the electronic pathways in both electrodes of a solid oxide electrolyzer cell.   [1] K. Thydén, Y.L. Liu and J.B. Bilde-Sørensen, Solid State Ionics 178, 1984–1989 (2008).  

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Tracking Electronic Pathways in Energy Materials by Low Voltage Scanning Electron Microscopy

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