High Temperature Water Electrolysis Using Metal Supported Solid Oxide Electrolyser Cells

Transcription

1 High Temperature Water Electrolysis Using Metal Supported Solid Oxide Electrolyser Cells G. Schiller, A. Ansar, O. Patz Deutsches Zentrum für Luft- und Raumfahrt (DLR) Pfaffenwaldring 38-4, D-7569 Stuttgart, Germany CIMTEC 21 5 th Forum on New Materials, Montecatini Terme, Tuscany, Italy, June 13-18, 21

2 Outline Introduction Metal supported cells (MSC) according to DLR spray concept Results of electrochemical characterisation of MSC cells and single repeating units (SRU) Degradation behaviour during electrolysis operation Conclusion CIMTEC 21 5th Forum on New Materials, Montecatini Terme Tuscany, Italy, June 13-18, 21 Institute for Technical Thermodynamics > Electrochemical Energy Technology

3 Thermodynamics of Electrolysis Reaction 4 Spec. Energy (kwh/m 3 H 2 ) Liquid water Steam H (total energy demand) G (electric energy demand) Q=T S (Heat demand) Temperature ( C)

4 Motivation - Thermodynamik der Elektrolysereaktion Zum Vergleich: Alkalische Elektrolyse von Wasser bei 8-85 C Zersetzungsspannung 1,9-2,3 V Stromverbrauch rund 4,5-5,5 kwh/m 3 H 2 bei 3 bar (Zdansky-Lonza-Verfahren) etwa 2% weniger Quelle: Schnurnberger, W., Wittstadt, U. and Janßen, H. (24) Wasserspaltung mit Strom und Wärme. In: Themenheft 24: Wasserstoff und Brennstoffzellen - Energieforschung im Verbund, url:

5 Metal-Supported SOFC Plasma Deposition Technology Thin-Film Cells Ferritic Substrates and Interconnects Compact Design with Thin Metal Sheet Substrates Brazing, Welding and Glass Seal as Joining and Sealing Technology oxygen/air not used air air channel fuel channel Bipolar plate protective coating contact layer cathode current collector cathode active layer electrolyte anode porous metallic substrate Bipolar plate fuel brazing not used fuel + H O 2 (not in scale) 3 m 25 m 35 m

6 Vacuum Plasma Spraying of SOFC Cells

7 Properties of VPS cells on IT11 substrates Reference Composition Thickness (µm) Fabrication route Functional Layer Substrate Plansee IT11 Fe-26Cr (Mn, Mo, Ti, Y 2 O 3 ) PM Barrier Layer H.C. Starck La.6 Sr.2 Ca.2 CrO APS Anode Gen4 NiO-YSZ (1:1 mass) 4-6 APS Electrolyte Gen3 9.5 mol% YSZ 4-6 VPS Cathode Gen3 LSM/LSCF LSM/LSCF APS Screen printed

8 Interdiffusion of metallic species (Ni into substrate, Fe into anode) Linescan ITV Fe, Cr Ni hits 2 15 Fe K Cr K Ni K Zr L distance in μm

9 Metallographic cross section of a VPS cell with diffusion barrier layer LaSrMnO 3 -cathode 8YSZ-electrolyte 8YSZ-electrolyte Ni/8YSZ-anode La.7 Sr.15 Ca.15 CrO 3 -barrier layer Porously sintered ferrite plate

10 Experimental set-up for cell characterisation

11 Experimental set-up for characterisation of circular cells

12 Overview of cells tested at DLR Nomenclature Substrate BekNi Ni-Felt BekNi ITV3_673 ITV3_672 ITV2_673 IT 126 IT 125 IT 1 IT 18 IT 28 IT 4 and IT 5 IT 25 IT 27 IT11 Barrier layer Cathode LSM Screenpr. LSM Screenpr. LSM Screenpr. LSM Screenpr. VPS LSM Screenpr. VPS LSM Screenpr. VPS LSM Screenpr. VPS LSCF VPS PVD LSCF VPS VPS LSCF VPS PVD LSM VPS PVD LSM VPS Period Comment Fuel Cell Mode Electrolysis Mode Variations x x 5/7% 32 h x x 221 h Long-Term Measurement Air cut off x x 114 h,.2 Acm -2 Reduction, Reference Performance Collapse Canceled due to Thermocycle and Restart Problems Reduction, Reference Furnace Breakdown Reduction, Reference Completely Plasmasprayed Interconnect Measurements Reduction, Reference Interconnect Measurements x x x x x x 5-9% Temp. EIS ocv loaded Polished Micrograph Section Further 5 h,.2 Acm h,.15 Acm -2 x 36 h,.15 Acm -2 x x 75 h,.2 Acm -2 to EMPA Investigation to EMPA, Linescan to EMPA Fractured, Point/EDX 166 h,.15 Acm -2 x x to EMPA 1 h,.25 Acm -2 x x Temp. >22 h,.3 Acm -2 x x x Temp. 4 h,.3acm -2 x x x 115 h,.3 Acm -2 x

13 I-V curves of cell IT1 in fuel cell and electrolysis mode 1,4 1,3 3 2 cell voltage U in V 1,2 1,1 1,9,8,7,6 Temp. = 8 C; Gasflow 4/23//16 smlpm/cm² H2/H2O//Air (37% Steam), p(i) U(i) current density i in ma/cm² h h power density p in mw/cm²

14 I-V curves of cell IT1 as a function of temperature at 43% humidification 1,4 1 1,3 cell voltage U in V Gasflow = 4/3//16 smlpm/cm² H2/H2O//Air (43% Steam) p(i) 1-296h, 8 C 2-292h, 75 C 1,2 1,1 1,9,8,7 U(i) power density p in mw/cm² 3-314h, 85 C,6, current density i in ma/cm²

15 I-V curves of cell IT1 as a function of temperature at 66% humidification 1,4 1 1,3 cell voltage U in V Gasflow 24/46//16 smlpm/cm² H2/H2O//Air (66% Steam) p(i) 1-171h, 8 C 1,2 1,1 1,9,8,7 U(i) power density p in mw/cm² 2-29h, 75 C h, 85 C,6, current density i in ma/cm²

16 I-V curves of cell IT1 as a function of temperature at 92% humidification 1,4 1 cell voltage U in V Gasflow 8/9//16 smlpm/cm² H2/H2O//Air (92% Steam) p(i) U(i) 1-244h, 8 C 2-249h, 75 C 3-32h, 85 C 1,3 1,2 1,1 1,9,8,7, power density p in mw/cm², current density i in ma/cm²

17 Microstructure of cell IT1 after 5 h of operation

18 I-V curves of cell IT28 in fuel cell and electrolysis mode as a function of temperature 1,4 75 1,3 5 1,2 p(i) 25 cell voltage/v 1,1 1,9,8, h, 8 C 2-195h, 75 C 3-199h, 85 C U(i) power density/mw cm -2,6-125 gas flow : 4/16//16 ml min -1 cm -2 H 2 /H 2 O//air (3% steam), current density/ma cm -2

19 Complete test run of cell IT28 1,6 temperature 8 1,4 7 1,2 6 voltage/v, ph2o/atm 1,8,6,4,2 varied electrolysis voltage -.3 A cm - ² electrolysis +26 mv /1h (2,1%/1hr) +46 mv /1h (3,9%/1hr) H 2 O-ratio U/V ph2o/bar T/ C time/hr temperature/ C

20 Change in impedance spectra of cell IT28 at OCV during long-term electrolysis 1 It28, ocv 8 C, 4/3//16 slpm H 2 /H 2 O//Air (43% Steam) h h h Z in mω cm² φ in 5 1 1,E-1 1,E+ 1,E+1 1,E+2 1,E+3 1,E+4 1,E+5 1,E+6 f in Hz

21 Change of impedance spectra of cell IT28 at 4 ma/cm 2 in fuel cell mode 1 It28,.4 A/cm 2 + Fuel Cell 8 C, 4/3//16 slpm H 2 /H 2 O//Air (43% Steam) h h h Z in mω cm² 12 8 φ in 4 1 1,E-1 1,E+ 1,E+1 1,E+2 1,E+3 1,E+4 1,E+5 1,E+6 f in Hz

22 Change of impedance spectra of cell IT28 at 4 ma/cm 2 in electrolysis mode h h h Z in mω cm² It28,.4 A/cm 2 - Electrolysis 8 C, 4/3//16 slpm H 2 /H 2 O//Air (43% Steam) φ in ,E-1 1,E+ 1,E+1 1,E+2 1,E+3 1,E+4 1,E+5 1,E+6 f in Hz

23 SEM micrographs of cross sections of cell IT28 after 2425 h of operation

24 EDX linescan of cell IT28 after 2425 h of operation Linescan2, IT hits 8 6 Fe K Cr K Ni K Zr L La L distance in μm

25 Cell IT4 (LSM O 2 -electrode with Pt mesh) and coated interconnect

26 I-V characteristics of cell IT4 with Pt mesh and interconnect in fuel cell and electrolysis mode 1,4 4 1,3 p(i) 2 1,2 cell voltage/v 1,1 1,9,8, h, interconnect 2-83 h, cathodic probe 3-29 h, interconnect 4-29 h, cathodic probe U(i) power density/mw cm -2 8 C,6 4/3//16 ml min -1 cm -2 H 2 /H 2 O//air (43% steam) -12, current density/ma cm -2

27 Complete test run of cell IT4 1,7 1,6 1,5 1,4 temperature U(interconnector)/V U(cell)/V T(interconnector)/ C 8 7 voltage/v 1,3 1,2 1,1 1,9,8,7,6 voltage probe interconnector voltage probe cathode -4 mv /186 h -12 mv /752 h (-1.5% /1 hr) possible effect of failure of other cell IT temperature/ C,5,4 SRU : Cell IT4 / interconnect -.3 A cm -2, electrolysis mode, 8 C 4/3//16 ml min -1 cm -2 H 2 /H 2 O//air (43% steam) 1, time/hr

28 Conclusion Metal supported cells show good electrochemical performance during electrolysis operation: 1.3 V at 1 A/cm 2 at 85 C 1.4 V at 1 A/cm 2 at 8 C For comparison: Electrochemical performance of alkaline water electrolysers 1.6 V at.3 A/cm 2 at 8 C (advanced Raney-Ni electrodes) V at.3 A/cm 2 at 8 C (standard Ni electrodes) Cell performance is improving with higher temperature and higher steam content Degradation during electrolysis operation (3.2%/1 h) is significantly higher than in fuel cell operation and needs further improvement Impedance spectra revealed a significantly enhanced polarisation resistance during electrolysis operation compared to fuel cell operation which was mainly attributed to the hydrogen electrode.

29 Acknowledgment I d like to thank my co-workers Dr. Asif Ansar, Dr. Michael Lang, Dorothea Lehmann and Olaf Patz for their scientific work and strong effort. Financial support within the EU project Highly Efficient High Temperature Hydrogen Production by Water Electrolysis (Hi2H2) is gratefully acknowledged.