SOFC advances and perspectives

Transcription

1 SOFC advances and perspectives John T. S. Irvine University of St Andrews Warwick 31st January 2019

2 Applications Transport Stationary Residential Distributed Cogeneration Portable Premium UPS Military Leisure Fuel Cells

3 Operation of a Solid Oxide Fuel Cell

4 Fuel Cells Electrochemically combust fuels high efficiency 70% chemical to electrical Highly scalable Decentralised - renewables Fuel flexibility silent clean quality power

5 Bloom Energy SOFCs running on Natural Gas and Biogas 250kW units Electrons not Fuel Cells Selling kwh not kw

6 HEXIS Galileo 1000 N: Installation St Andrews Buchanan Building Boiler House.

7 Solid Oxide Cells

8 Performance Technology Drivers Materials, microstructure and processing, system management Durability Materials, temperature, system Cost Manufacture, materials Fuel Flexibility Materials, system management Retain focus on clean energy target Whole cycle analysis

9 Contents Introduction System/Performance Fuels Processing Materials Durability Nanostructures

10 The rate at which work is done by a system equals net enthalpy and entropy differences associated with the flow streams W m ( h T0 s) T0 P s Reversible potential / Nernst potential E rev Efficiency considerations cell level RT F P O2 ( a) ln 4 PO ( c) Fuel cell efficiency 2 Overall efficiency product of the electrochemical efficiency E, and heating efficiency H. The electrochemical efficiency is the product of the thermodynamic efficiency T, the voltage efficiency V and the current or Faradic efficiency J :

11 Voltage efficiency When an electrical current is drawn from a fuel cell, part of the chemical potential available must be used to overcome the irreversible internal losses.: V This cell overpotential comprises the total ohmic losses for the cell, and the polarization losses associated with the electrodes. The useful voltage under load conditions can therefore be expressed as: V E E E IR r an cath

12 Effect of fuel utilization on voltage efficiency and overall cell efficiency for typical SOFC operating conditions (800 C, 50% initial hydrogen concentration). At 90% fuel utilization, the Nernst voltage drops by over 200 mv. As a consequence, the maximum cell efficiency (on a higher heating value basis) is not 62%, as predicted based on the ideal potential, but 54%. Fuel Cell Handbook (Seventh Edition), EG&G Technical Services DOE Contract No. DE-AM26-99FT40575

13 System Considerations Efficiency losses also at system level Heat Efficiency can also be improved by system Using Available Heat Combined Heat and Power Combined with Gas Turbine Utilisation of waste heat in SOFC system Integration with other processes Reforming of Hydrocarbon Fuel

14 Contents Introduction System/Performance Fuels Processing Materials Durability Nanostructures

15 The concepts and steps for fuel processing of gaseous, liquid and solid fuels for high temperature and low temperature fuel cells C.Song, Catalysis today, 77 (2002) 17-49

16 Biogas Biogas is a mixture of 60 to 70% methane and 30 to 40% CO 2 with some H 2 S (Hydrogen Sulfide), that burns similar to socalled natural gas, which is a fossil fuel.

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18 Contents Introduction System/Performance Fuels Processing Materials Durability Nanostructures

19 Challenges for Future Endurance Prevent or slow down degradation? Performance Nanomaterials required New Materials Cannot compete, too difficult to implement Oxide Anodes Cannot compete on performance with Ni/YSZ Electrolysis Pure Steam, no safe gas In situ renewal

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21 Temperature Lower Operating Temperature Can use less costly interconnect materials Avoids sealing problems Requires higher conductivity electrolytes >0.1Scm -1 La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3, Gd 1-x Ce x O 2-x/2 or protonics Alternatively, supported zirconia electrolyte films (10m) High Temperature o C Favours combined heat and power operation Essential for combined cycle operation Can integrate reforming technology (700 o C)

22 Implementation of New Materials

23 SOC Electrode Design Schematic of electrode materials palette

24 A 2 B 2 O 5 ( a) A A BO 3 ( b) A A B O 2 6 (c) B 2 O5 A A Progress in Solid State Chemistry 35 (2007)

25 SAED pattern of PrBa 0.50 Sr 0.5 Co 2 O 5+ at RT viewed down the [100] (a) and [010] (b) zone axis Doubling of axes

26 Cell parameter, a (A) Cell parameter, c (A) cell param vs temp a c Temperature ( o C)

27 SBSCO Composites with Ceria

28 Infiltration/Impregnation Routes a b c (a) Electron conducting perovskite titanate backbone, (La,Sr,Ca) 1-a TiO 3, is infiltrated with surface also modified by fine layer of CGO MIEC (b) YSZ backbone coated with a MIEC perovskite, (La,Sr)(Cr,Mn)O 3 JTS Irvine, D Neagu, MC Verbraeken, C. Chatzichristodoulou, C Graves & MB Mogensen, Nature Energy 1, (2016)

29 Impregnation of La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3 G Corre, G Kim, M Cassidy, J Vohs, R Gorte, and JTS Irvine, Chem. Mater., 2009, 21,

30 Galileo Stack 750 W with 3.3 kw reformed CH 4 input + CeO 2 + CeO 2 + Ni

31 Surface energy of potential materials LSCT Wetting studies

32 Voltage (V) Power (W) a b 1.0 Ni/CGO 900 C Ru/CGO 900 C Rh/CGO 900 C Pt/CGO 900 C Pd/CGO 900 C c d 0.2 SEM images of the fuel electrode backbone microstructures (screen printed with a 230 mesh screen) for samples sintered at: a) 1325 C/1h, b) 1325 C/2h, c) 1350 C/1h and d) 1350 C/2h Current (A cm 2 ) I-V-P curves for Ni/CGO, Ru/CGO, Rh/CGO, Pt/CGO and Pd/CGO impregnated fuel cell anodes acquired at 900 C

33 Voltage (V), Temp ( C) Current Density (A cm 2 ) Long-Term SOFC Test with Impregnated LSCT A- Anode Current Source Issue Voltage V Temp C Current Density Time (h) Voltage, current and temperature profiles for a SOFC with impregnated LSCT anode acquired at 850 C in H 2 0

34 Microstructure is critical reactions occur at interface e.g. Ni/yttria zirconia fuel electrode in SOFCs

35 Air electrode evolution (La,Sr)MnO 3 )

36 Fuel electrode evolution (Ni/YSZ)

37 Performance Technology Drivers Materials, microstructure and processing, system management nano is beneficial Durability Materials, temperature, system nano is problematic Cost Manufacture, materials nano can be expensive Fuel Flexibility Materials, system management - nano is beneficial Retain focus on clean energy target Whole cycle analysis

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39 Terrace separation Terrace edge La 0.4 Sr 0.4 Ni x Ti 1-x O 3-x/2 (x = 0.03, 5% H 2, 930 C, 20h then wet 5% H 2, 900 C, 100h) nm

40 Coking on deposited Ni

41 Coking on Exolved Ni D. Neagu, T-S. Oh, DN. Miller, H. Menard, SM. Bukhari, SR. Gamble, RJ. Gorte, JM. Vohs, JTS. Irvine. Nat. Commun. 2015, 6, 8120

42 Switching on electrocatalytic activity in solid oxide cells Electrochemical vs Chemical Reduction La 0.43 Ca 0.37 Ni 0.06 Ti 0.94 O 3-γ J-H. Myung, D. Neagu, DN. Miller & JTS. Irvine, Nature, ,

43 Electrode with in situ exsolved metal particles Electrolyte

44 After reduction in 5%H 2 Microstructures of as-prepared electrode, before any reduction Figure 1(e)

45 Reduction by H 2 at 900 C for 20 h Chemical reduction Compared to Electrochemical Switching Under 50% H 2 O/N 2, 900 C, 150 s

46 On switching after 100 h of fuel cell testing at 750 C in 3% H 2 O/H 2 at 0.7 V After stability testing

47 Solid oxide cell based on electrochemical switching. Current-voltage curves ( ) and Cell power curves ( ) illustrating operation at different temperatures in fuel cell mode in 3% H 2 O/H 2

48 Solid oxide cell based on electrochemical switching. Current-voltage curves for electrolysis mode under 50% H 2 O/N 2 Showing equivalent H 2 production assuming 100% Faradaic efficiency

49 5% H 2 /N 2 (po 2 ~ atm) 50% H 2 O/N 2 (po 2 ~ atm) - + 2V

50 Overall Perspective We need to save CO 2 now, 2050 may be too late Offshoring is not acceptable Globally Energy Poverty needs to be addressed Waste to Energy, plastics Improving efficiency Distributing Electricity Stationary Fuel Cells

51 Acknowledgements Elena Stefan, Mark Cassidy, Cristian Savaniu, Maarten Verbraeken, Robert Price, Georgios Triantafyllou, Damiano Bonaccorso, Aida Fuente Cuesta Dragos Neagu, Jae-Ha Myung, Gael Corre University of St Andrews Ueli Weissen, Boris Iwanschitz, Andreas Mai Hexis AG Mogens Mogensen, Peter Holtappels DTU Ray Gorte, John Vohs, Guntae Kim UPenn

52 Acknowledgements EPSRC ONR EU Scotas EU Metsapp Royal Society NSF Materials World