Transmission electron microscopy a versatile tool to study the microstructure of HT-PEMFC

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Transmission electron microscopy a versatile tool to study the microstructure of HT-PEMFC Düsseldorf, Germany Christina Scheu Acknowledgement K. Hengge, S.

1 Transmission electron microscopy a versatile tool to study the microstructure of HT-PEMFC Düsseldorf, Germany Christina Scheu Acknowledgement K. Hengge, S. Gleich Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany C. Heinzl, T. Ossiander, M. Welsch, M. Perchthaler Elcore GmbH, Munich, Germany V. Hacker Graz University of Technology, Graz, Austria

2 2 MOTIVATION Need for green energy SUN BUT: seasonal conditions, daytime, over- and underproduction, energy peaks Energy needs to be stored One possibility: hydrogen fuel Use at any time in fuel cells (FC) possible

3 NEW MATERIALS FOR HT-PEMFCS High-Temperature Polymer-Electrolyte-Membrane Fuel Cell (HT-PEMFC) stack e - Anode Cathode e - Membrane H 2 O 2 AIM of the work: Develop new materials for HT-PEMFCs Link

3 3 NEW MATERIALS FOR HT-PEMFCS High-Temperature Polymer-Electrolyte-Membrane Fuel Cell (HT-PEMFC) stack e - Anode Cathode e - Membrane H 2 O 2 AIM of the work: Develop new materials for HT-PEMFCs Link microstructure and properties Discover degradation mechanisms H 2 O Membran-Electrode-Assembly (MEA) In our work: Microstructural features of interest are on the nanometer scale High spatial resolution techniques are required Scanning electron microscopy (SEM) Focussed ion beam sectioning (FIB) Transmission electron microcopy (TEM) and related techniques

1 nm Monochromated electron gun Chemical

$diffraction 1.133 2 nm 1.$ s -probe corrector 2.265 1.962 1.

4 Intensity [a. u.] TEM AND RELATED TECHNIQUES HRTEM > 0.1 nm Monochromated electron gun Chemical composition and distribution maps via EDX diffraction nm of 4 SDD-EDX detectors 3-condenser system C s -probe corrector Annular STEM detector Sample holder Bonding states via EELS HRSTEM > 0.1 nm O-K-edge High resolution, high speed energy filter Energy loss [ev] 1.5 nm 4

5 NEW MATERIALS FOR HT-PEMFCS e - e - H 2 O 2 H 2 O Anode 5,6 Pt catalyst on tungsten suboxide Membrane 1-4 Polybenzimidazole (PBI) Cathode Pt catalyst NP on amorphous carbon (1) Heinzl, C.; Ossiander, T.; Gleich, S.; Scheu, C. J Membrane Sci 2015, 478, 65. (2) Ossiander, T.; Heinzl, C.; Gleich, S.; Schönberger, F.; Völk, P.; Welsch, M.; Scheu, C. J Membrane Sci 2014, 454, 12. (3) Ossiander, T.; Perchthaler, M.; Heinzl, C.; Scheu, C. Journal of Power Sources 2014, 267, 323. (4) Ossiander, T.; Perchthaler, M.; Heinzl, C.; Schönberger, F.; Völk, P.; Welsch, M.; Chromik, A.; Hacker, V.; Scheu, C. J Membrane Sci 2016, 509, 27. (5) Perchthaler, M.; Ossiander, T.; Juhart, V.; Mitzel, J.; Heinzl, C.; Scheu, C.; Hacker, V. Journal of Power Sources 2013, 243, 472. (6) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F280. 5

HT-PEM Electrodes 6 Development of new electrodes for HTPEM-FC usually high surface area carbon (HSAC) is used as catalyst support due to high potentials and temperatures this carbon catalyst support

6 HT-PEM Electrodes 6 Development of new electrodes for HTPEM-FC usually high surface area carbon (HSAC) is used as catalyst support due to high potentials and temperatures this carbon catalyst support oxidizes to CO 2 possible replacement by WC or WO 3-x based systems (as anode material) Benefits of using WO 3-x as anode material WO 3 is an electrical insulator while WO 3-x is a semiconductor (band gap ev) melting temperature > 1700 C corrosion resistant CO-tolerant H+-conductivity WO 3-x catalyst support Tungsten materials as durable catalyst supports for fuel cell electrodes M. Perchthaler, T. Ossiander, V. Juhart, J. Mitzel, C. Heinzl, C. Scheu, V. Hacker Journal of Power Sources, 243, (2013)

Pt loaded Anode SEM Pt loaded WO 3-x prior application as

catalyst support due to high potentials and temperatures WO

possible replacement by WC or WO x based systems Pt

200 nm 50 nm 2.5 nm C. Heinzl, K. A. Hengge, M.

7 Pt loaded Anode SEM Pt loaded WO 3-x prior application as an anode usually high surface area carbon is used as catalyst support due to high potentials and temperatures WO this 3-x carbon support catalyst support oxidizes to CO 2 possible replacement by WC or WO x based systems Pt octahedra 13 3 µm 400 nm FIB lamella HRTEM TEM crosssection 200 nm 50 nm 2.5 nm C. Heinzl, K. A. Hengge, M. Perchthaler, V. Hacker, and C. Scheu, J. Electrochem. Soc., 162, 3, F280-F290, (2015) 7

8 Normalized cell voltage [%] DEGRADATION BEHAVIOR OF HT-PEMFCS (1) e - e- Anode Cathode H 2 O 2 H 2 O 4 MEAs 3 different operation modes and times Ready to use 650 h of continuous operation 2000 h of continuous operation Pt on WO 3-x PBI Pt on C Start-stop cycles Unintended shutdowns of stack Runtime [h] (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F280. 8

DEGRADATION BEHAVIOR OF HT-PEMFCS (1) 2000 h of

SEM EDX Map shows elemental distribution STEM

investigation of highlighted areas Membrane W-L

3-x O-K Membrane 50 µm P-K C-K Pt-L Tungsten

Heinzl, C.; Hengge, K. A.; Perchthaler, M.

9 DEGRADATION BEHAVIOR OF HT-PEMFCS (1) 2000 h of continuous operation insights via SEM and TEM: SEM EDX Map shows elemental distribution STEM Interface between anode and membrane TEM investigation of highlighted areas Membrane W-L Anode Cathode Hole due to FIB cutting Pt on WO 3-x O-K Membrane 50 µm P-K C-K Pt-L Tungsten suboxide Hole due to FIB cutting 1 µm (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F280. 9

DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of PLATINUM networks

100 nm 100 nm 100 nm 100 nm Well defined network Many pores Pt networks become

the interface between anode and membrane (1) Heinzl, C.; Hengge, K. A.

10 DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of PLATINUM networks Reference 650 h 2000 h Start-stop cycles a) b) c) d) WO x grains Pt on WO x 100 nm 100 nm 100 nm 100 nm Well defined network Many pores Pt networks become deformed Number of pores decreased Only present on WO 3-x grains Located at the interface between anode and membrane (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F

DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of WO 3-X based areas Reference 650 h 2000

nm Facetted and rounded Randomly arranged WO 3-x grains Start-stopp Platinum only between

of oxidation state in the bulk material 2000 h 600 h Reference (1) Heinzl, C.; Hengge, K. A.

11 DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of WO 3-X based areas Reference 650 h 2000 h Start-stop cycles a) b) c) d) Pt on WO 3-x WO 3-x grain 100 nm (-2-32) 100 nm 100 nm 100 nm Facetted and rounded Randomly arranged WO 3-x grains Start-stopp Platinum only between randomly arranged WO 3-x grains Single crystalline grains; sizes up to 1 µm EELS: no change of oxidation state in the bulk material 2000 h 600 h Reference (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F

DEGRADATION BEHAVIOR OF HTPEM FCS (1) Comparison of CARBON

c) d) MEA III Pt on C carbon 100 nm 100 nm 100 nm 100 nm Pt:

nanoparticles 7.3 ± 1.5 nm 10.0 ± 3.4 nm 12.5 ± 3.8 nm 7.

9 nm Pt near WO 3-x grains Pt diffusion into carbon based

12 DEGRADATION BEHAVIOR OF HTPEM FCS (1) Comparison of CARBON based areas Reference 600 h 2000 h Start-stopp cycles a) b) c) d) MEA III Pt on C carbon 100 nm 100 nm 100 nm 100 nm Pt: elongated crystals Pt: individual, spherical shaped nanoparticles 7.3 ± 1.5 nm 10.0 ± 3.4 nm 12.5 ± 3.8 nm 7.1 ± 1.9 nm Pt near WO 3-x grains Pt diffusion into carbon based areas (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F

DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of MEMBRANE based

2,5 nm Membrane 100 nm 100 nm 100 nm 100 nm Pure PBI Pt particles in

5 nm highest stress on Pt catalyst (1) Heinzl, C.; Hengge, K. A.

13 DEGRADATION BEHAVIOR OF HT-PEMFCS (1) Comparison of MEMBRANE based areas Reference 650 h 2000 h Start-stop cycles a) b) Pt in PBI c) d) 2,5 nm Membrane 100 nm 100 nm 100 nm 100 nm Pure PBI Pt particles in the membrane material 5.4 ± 0.7 nm 2.9 ± 0.5 nm 3.7 ± 0.5 nm highest stress on Pt catalyst (1) Heinzl, C.; Hengge, K. A.; Perchthaler, M.; Hacker, V.; Scheu, C. Journal of The Electrochemical Society 2015, 162, F

14 14 SUMMARY NEW ELECTRODE MATERIALS e - e - Anode Cathode H 2 O 2 H 2 O Degradation during FC operation: Holes Pt on WO 3-x No changes of bulk WO 3-x 100 nm Membrane Pt structures become dense 100 nm 100 nm Tungsten suboxide Holes 1 µm Pt diffuses into membrane 100 nm

15 HT-PEMFC Membrane Development of new membrane to improve proton conductivity chemical modification, doping, to improve mechanical stability addition of SiO 2 nanoparticles Pure PBI based membrane Modified PBI based membrane PBI: Polybenzimidazole TEOS: tetraethoxysilane 15

16 Frequency / % HT-PEMFC Membrane Modified membranes obtained with different tetraethoxysilane (TEOS) contents EDS measurements on particles and particle free regions % 80% 120% higher concentration of tetraethoxysilane (TEOS) larger size of silica nanoparticles higher particle density in the membrane Particle size / nm 2 T. Ossiander*, C. Heinzl*, S. Gleich, F. Schönberger, P. Völk, M. Welsch, C. Scheu, J. Membr. Sci. 2014, 454, T. Ossiander, M. Perchthaler, C. Heinzl, C. Scheu. Journal of Power Sources 2014, 267,

17 Performance Modified membranes obtained with different tetraethoxysilane (TEOS) contents best performance obtained for membranes with 40% TEOS High performance in stack tests and low degration rate! Good mechanical properties. T. Ossiander*, C. Heinzl*, S. Gleich, F. Schönberger, P. Völk, M. Welsch, C. Scheu, J. Membr. Sci. 2014, 454,

18 HT-PEMFC Membrane Membranes fabricated with 40% TEOS, one has a further thermal treatment (at 70 C): M1 70 C M2 RT C. Heinzl, T. Ossiander, S. Gleich, and C. Scheu Journal of Membrane Science, 478, (2015) 18

HT-PEMFC Membrane Further thermal treatment (at 70 C) leads to additional large SiO 2 particles: detected elements: C, N (PBI) Si, O (silica) C Si O P, K (additives) 500 nm Good

19 HT-PEMFC Membrane Further thermal treatment (at 70 C) leads to additional large SiO 2 particles: detected elements: C, N (PBI) Si, O (silica) C Si O P, K (additives) 500 nm Good mechanical properties achieved by incorperating larger particles, but performance is lower C. Heinzl, T. Ossiander, S. Gleich, and C. Scheu Journal of Membrane Science, 478, (2015) 19

New Materials for HT-PEMFC 20 Tungsten oxide as promising electrode material: slightly reduced performance better degradation behavior different parts of anode show different degradation mechanisms

20 New Materials for HT-PEMFC 20 Tungsten oxide as promising electrode material: slightly reduced performance better degradation behavior different parts of anode show different degradation mechanisms 200 nm 200 nm Incorporation of silica particles (40% TEOS) in PBI based membranes leads to increase in: mechanical stability (compared to PBI lifetime performance Increase of temperature during synthesis: additional large silica particles increased mechanical stability slightly lower performance

21 Thanks to Katharina Hengge Stephan Gleich Christoph Heinzl Markus Perchthaler Marina Welsch Tanja Ossiander Viktor Hacker 21