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Development of Porous LaNi0. 6Fe0
Development of Porous LaNi0.6Fe0.4O3 Electrodes with tailored microstructure for High Temperature and Pressure Alkaline Electrolysis Cells Jens Q Adolphsen1, Bhaskar R. Sudireddy1, Vanesa Gil1, Christodoulos Chatzichristodoulou1 and Lennart Bergström2 1 Department of Energy Conversion and Storage , Technical University of Denmark 2 Department of Materials and Environmental Chemistry, Stockholm University Who am I, where do I work Work performed during last 4 month at Stockholm University Today I will focus on the characterization and processing and not the technology
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ECerS conference 2017, Budapest
Outline Motivation Stabilization of LaNi0.6Fe0.4O3 (LNF) in aqueous media Rheological characterization of LNF suspensions Microstructural characterization of sintered LNF layers Conclusion and outlook ECerS conference 2017, Budapest
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ECerS conference 2017, Budapest
Motivation Bimodal porosity distribution with pore sizes around nm and 2-10 µm respectively 3D interconnected open porous network Conventional, easily scalable processing methods; e.g. screen printing, dip coating or tape casting Various strategies to process microstructures with a bimodal porosity distribution: templating, freeze casting 3D interconnected network of both “meso”- and macropore phase Most appropriate method, taken the desired pore sizes into account, was the sacrificial pore size approach combined with only partial sintering Pore formers, starch, combined with a partial sintering was chosen as the method of choice ECerS conference 2017, Budapest
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ECerS conference 2017, Budapest
Suspensions LaNi0.6Fe0.4O3 powder (SSABET=12.6 m2/g) Water Dispersants PVP k15 (10,000 g/mol) PMAA-NH4 (15,000 g/mol) PAA (5,000 g/mol) Pore former Rice starch Size = 4.3±1.3 µm J. Suntivich et al., Nature Chem. 3 ( ), 2011 Motivation for using LNF: Perovskites have shown good activity towards the OER in alkaline media LNF was of particular interest High electronic conductivity Not adequate chemical stability Steric: PVP Electrosteric: PMAA-NH4 is very similar to PAA but it is a buffered system Rice starch is the smallest starch type ECerS conference 2017, Budapest
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Sedimentation analysis
1.5 vol% LNF suspensions ball milled 84 h PVP, 14 days 0.25 mg/m2 0.79 mg/m2 2.5 mg/m2 8.0 mg/m2 PAA, 6 days 0.5 mg/m2 0.75 mg/m2 1.0 mg/m2 Motivation: Larger particles sediment faster Sedimentation – PVP sediments very slowly compared to PMAA PAA sediment slowly but it is quite acidic (pH ~3 when adding powder), which is a problem as LNF is not stable in acidic conditions PMAA, 48 h PMAA, 4 h 0.25 mg/m2 0.5 mg/m2 0.75 mg/m2 1.0 mg/m2 0.25 mg/m2 0.5 mg/m2 0.75 mg/m2 1.0 mg/m2 ECerS conference 2017, Budapest
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Particle size measurements
Added small amount to water, shaken, rest (to remove large agglomerates), no pre-ultrasonification PVP and PMAA ECerS conference 2017, Budapest
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Zeta potential measurements
zeta potential decreases with the zeta potential – screening effect PVP and PAA show essentially similar behaviour Powder surface is positive and IEP at high pH PAA and PMAA are similar but PMAA is a buffered system making it harder to shift the pH ECerS conference 2017, Budapest
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Rheological characterization
A pre-rotational shear (10 s-1 for 2 min) was performed before of the followsing step: Pre-oscillatory shear (10 rad·s-1, 0.1%) Amplitude sweep at 10 rad·s-1 Frequency sweep in LVE Flow curve ( s-1) Rotational shear at 10 s-1 for 2 min Rheology performed with the same sample The pre-shear seemed to ”reset” the sample Of interest to understand the suspension and for further processing Concentric cup and cylinder (CC27) measuring system from Anton Paar GmbH ECerS conference 2017, Budapest
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Rheological characterization – flow curves
PMAA had to be dilluted with water Rice starch modifies viscosity of PVP stabilised suspensions suspension significantly Poor fluidity of PMAA suspensions Rice starch has little influence on the viscosity of the PMAA stabilised suspensions significantly ECerS conference 2017, Budapest
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Rheological characterization – Amplitude sweeps
PVP suspension are liquid like without starch and viscoelastic with starch PMAA suspensions are more gel-like. Week netwrork is formed. They do flow out of the bottle though ECerS conference 2017, Budapest
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Rheological characterization – Frequency sweeps
Rice Starch increases the G’ significantly in PVP suspensions At around 100 s-1 rice starch PVP suspensions starch to flow – similar G’ as the suspension without rice starch Rice starch has little influence on the rheology of the PMAA stabilised suspensions – dominated by particle network ECerS conference 2017, Budapest
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Deposition and sintering
Deposition by brush painting on sintered, meso-porous YSZ substrates Drying at 80 °C for 30 min to form a starch consolidation casted [1] layer Sintering ramp rate 1°C/min from °C /1 h holding 250°C / 1 h ramp rate 1°C/min from °C ramp rate 2°C/min from °C holding 1100°C / 1 h ramp rate 2°C/min °C Deposition on substrate Dryed at 80 deg C in water bath – starch swelling & gelatinization starch is supposed act as consolidator, binder and pore former SCC is also supposed to create less closed porosity [1] Lyckfeldt, O. and Ferreira, J. M. F., J. Eur. Ceramic Soc., 1998, 18, ECerS conference 2017, Budapest
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Microstructural characterization of sintered porous LNF layers
LNF, PVP and 25 vol% starch Cracked cross section LNF, PVP, 50 vol% starch Cracked cross section Significant different when comparing the macropores in 50vol% starch vs 25 vol% starch 10 µm 10 µm ECerS conference 2017, Budapest
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Microstructural characterization of sintered porous LNF layers
LNF w PVP & 25 vol% rice starch Cracked cross section LNF w PVP & 50 vol% rice starch Cracked cross section 1 µm 1 µm ECerS conference 2017, Budapest
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Microstructural characterization of sintered porous LNF layers
LNF, PVP, 25 vol% starch Top surface LNF, PVP, 50 vol% starch Top surface Similar fine mi 200nm 200nm ECerS conference 2017, Budapest
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Microstructural characterization of sintered porous LNF layers
LNF, PVP, 50 vol% starch Top surface LNF, PMAA, 50 vol% starch Top surface Coarse microstructure of PVP and PMAA stabilized suspensions similar Quite similar fine microstructure It is a top surface view and the PVP suspensions seem to have a better packing so a further quantitative comparisson of pore sizes would be of interest 200 nm 200 nm ECerS conference 2017, Budapest
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ECerS conference 2017, Budapest
Conclusion & outlook LNF structures with a dual porosity distribution have been achieved using PVP and PMAA as dispersant and rice starch as macro-pore former. Successfully implementing the gel consolidation casting step is expected to mitigate crack formation and delamination. A quantitative analysis of the pore sizes and electrochemical performance of the electrode layers are future plans PMAA suspensions not as homogenous packing PMAA is, however, not very convenient as it does not disperse the powder so only low solid loading suspensions can be obtained. Starch consolidation casting step is critical for crack free structures. Alternatively a binder and surfactant/co-solvent might have to be added 50 µm ECerS conference 2017, Budapest
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Acknowledgements Karen Brodersen and Søren Christensen DTU Energy
Hugo Voisin MMK, Stockholm University Karen Brodersen and Søren Christensen for help with making the mesoporous supports Hugo Voisin for helpful discussions on rheology
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