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Development of Oxygen Electrodes for High Temperature and Pressure Alkaline Electrolysis Cells (HTP-AEC) Jens Q Adolphsen Bhaskar R. Sudireddy, Vanesa Gil, Christodoulos Chatzichristodoulou
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ECerS conference 2017, Budapest
Outline Motivation for the work Selection of materials Electrochemical activity towards the OER Chemical stability of materials at high temperature Processing porous LaNi0.6Fe0.4O3 electrodes Motivation and past results (high current density compared to conventional alkaline electrolysis cells Low overvoltage (high efficiecy) ECerS conference 2017, Budapest
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High Temperature and Pressure Alkaline Electrolysis Cells (HTP-AEC)
Mesoporous Electrolyte matrix Motivation and past results (high current density compared to conventional alkaline electrolysis cells Low overvoltage (high efficiecy) Record data from earlier work 3.75 A/cm2 at 1.75 V with ηel = 85 % (200ºC, 20 bar) C. Chatzichristodoulou et al. J. Electrochem. Soc, 163, 2016 ECerS conference 2017, Budapest
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Selection of materials for the OER
O2(g)+ 2H2O(l) Electrochemical activity Electrochemical stability Electronic conductivity Electrode materials for the Oxygen Evolution Reaction (OER) 4e- 4 OH-aq ? Metal oxides Pervoskites active: Most active become amorphous over time Ni-Fe combination has proven to be a particularly good combination in NiFeOx Activity Stability
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Electrochemical Characterization
Materials Conditions RTP, N2 atmosphere, 1 M KOH, Measurements Chronopotentiometry at 0.5, 1.0, 2.0, 5.0, 10, 25 and 50 mA·cm-2 Amperostatic EIS LaNiO3 La0.97NiO3 LaNi0.6Fe0.4O3 La0.97Ni0.6Fe0.4O3 La2Ni0.9Fe0.1O4 Well-defined surface area Electronic conductivity: LN & LNF: S/cm L2NF: S/cm Reference electrode (RHE from Gaskatel) Working electrode (Au current collector) Counter electrode (Pt mesh) Separator
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Electrochemical Characterization
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Electrochemical Characterization
Material b (V/dec) η 10 mA/cm2 LaNiO3 0.083 0.38 La0.97NiO3 0.092 0.44 LaNi0.6Fe0.4O3 0.13 0.11 0.45 La2Ni0.9Fe0.1O4 0.079 0.40 IrOx [1] - 0.32 Ni0.9Fe0.1Ox [2] 0.030 0.34 PrBaCo2O5+x [3] ~0.07 ~0.38 [1] C. C. L. McCrory, S. Jung, J. C. Peters, T. F. Jaramilllo, J. Am. Chem. Soc. 135 ( ), 2013 [2] L. Trotochaud, J. K. Ranney, K. N. Williams, S. W. Boettcher, J. Am. Chem Soc. 134 ( ), 2012 [3] A. Grimaud, K. J. May, C. E. Carlton, Y-L. Lee, M. Risch, W. T. Hong, J. Zhou, Y. Shao-Horn, Nat. Commun. 4 ( ), 2013
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Electrochemical Characterization
Test with same pellet
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Sample roughness factors
RRMS (pre) [µm] RRMS (post) [µm] LaNiO3 0.41 0.79 La0.97NiO3 0.44 0.92 LaNi0.6Fe0.4O3 0.37 0.68 La0.97 Ni0.6Fe0.4O3 0.38 0.49 La2Ni0.9Fe0.1O4 0.20 0.81 Initial polished surface 1 µm Polished surface after electrochemical testing 1 µm
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Chemical Stability Porously sintered pellets and as-received powders exposed to concentrated KOH for a week at 100°C/220°C Pellets crumble after 1-2 weeks when exposed to 45 wt% KOH at 220 deg C Powder dilluted to remove KOH, heated to remove water and performed XRD
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Chemical Stability – XRD
Neither LN, LNF nor L2NF are stable at 220 deg C. They all fall apart and it is likely that secondary phases La, Ni and Fe are observed. It is not an attempt to tell you exactly what phases are formed ○LaNiO3 ● LaNi0.6Fe0.4O3 Δ La2Ni0.9Fe0.1O4 + La2O3 ♦ LaO(OH) ♠ La(OH)3 * NiO □ NiO(OH) ♥ Ni(OH)2 × Fe2O3 ◊ FeO(OH) ♣ Fe(OH)2
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Chemical Stability – XRD
L2NF is stable at 100 deg C. LN is starting to fall apart (mainly La(OH)3 phase being formed) LNF is not stable at all ○LaNiO3 ● LaNi0.6Fe0.4O3 Δ La2Ni0.9Fe0.1O4 + La2O3 ♦ LaO(OH) ♠ La(OH)3 * NiO □ NiO(OH) ♥ Ni(OH)2 × Fe2O3 ◊ FeO(OH) ♣ Fe(OH)2
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Processing of LNF electrode layers
Processing of porous structures for the oxygen evolution reaction % total porosity - Hierachical porosity macropores & mesopores Optimization of the microstructure of the porous electrode: - Allow transport of oxygen leaving the pores - Allow transport of OH- species to reactive sites Optimal pore size distribution Percolating phases (gas, solid) Mesoporosity Macroporosity
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Processing of LNF electrode layers
10 µm 200nm Motivation for using rice starch 200 µm
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Processing of LNF electrode layers
Top surface 10 µm Still some challenges – flat substrates Starch is less visible, adhesion is fine Cross section 10 µm
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Thank you for your attention
Acknowledgements Bent F. Hansen Jeanette Krambech Jens Østergaard Karen Brodersen Kjeld B. Andersen Lene Knudsen Søren Christensen Søren P. V. Foghmoes
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