MIXED-CONDUCTORS FOR ELECTRIC POWER APPLICATIONS*

Transcription

1 MIXED-CONDUCTORS FOR ELECTRIC POWER APPLICATIONS* U. (Balu) Balachandran Argonne, IL 60439, U.S.A. * Work supported by the U.S. Department of Energy. Argonne National Laboratory Office of Science U.S. Department of Energy A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago

2 The Research Council of Norway Nanotechnology and new Materials NANOMAT Two major priorities: develop new materials, with focus on functional materials focus on selected parts of nanotechnology FUNMAT (UiO, NTNU, SINTEF, IFE): Materials for hydrogen technology Catalyst and membrane materials Mixed-Conductors 2

3 Outline Introduction for Hydrogen Economy Mixed-conducting oxides Membranes for hydrogen production (fossil, renewable) Proton conductors (fuel cell, electrolyzer) - Prof. T. Norby (new proton conductors for fuel cells) Membranes for hydrogen separation/purification Nanoscale effects of ionic conductivity - Prof. O. M. Løvvik & Prof. J. Swenson (atomic scale modeling & influence of nanostructure) Research needs/challenges 3

4 Energy is as important to modern society as food and water What energy-producing technologies can be envisioned that will last for millennia, and just how many people can they sustain? 4

5 Why Hydrogen? Two specters threaten civilization - the prospect of economic disarray and incitement to war by the local depletion and global mal-distribution of high quality fossil fuels, especially oil - prospect of almost unimaginable environmental, economic and cultural disruption caused by climate volatility and triggered, primarily, by our energy system s CO 2 effluent Post-Petrolium Age 5

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7 Why Hydrogen? Hydrogen economy- a solution that holds the potential to provide sustainable clean, safe, secure, affordable, and reliable energy. 7

8 Mixed-Conductors for Hydrogen Production 8

9 Dense Mixed-Conductor vs. Ionic Conductor Mixed-conductor Ex: Perovskites, Brownmillerite Ionic conductor Ex: YSZ,CeO 2 Low po 2 High po 2 O - - O 2 e - air (O 2, N 2, ) O - - 1/2O 2 + 2e - 1/2O 2 + 2e - O - - V e - e - O - - O 2 air (O 2, N 2, ) Low p High p H + anode cathode No electrical circuitry/power supply Non-galvanic e -, CO 2, CO H + + e - 1/2 1/2 H + + e - Galvanic Fuel cell, O 2 generator, electrolyzer 9

10 Mixed-Conducting Dense Membrane For Natural Gas Conversion (Sr-Fe-Co-O) Reducing Atmosphere Oxidizing Atmosphere Methane (CH 4 ) O -- e - Air (O 2 /N 2 ) Demonstrated proof-of-concept of operation (1000 h) Industrial consortia are scaling up the process CH 4 + 1/2O 2 CO + 2 Migration through the Bulk U. Balachandran, et al., U.S. Patent 5,639,437 (June 17, '97); 5,723,074 (March 3. '98) 10

11 Incentives for Oxygen Membranes for Production Conventional natural gas steam reforming - CH 4 + O 3 + CO (endothermic; energy required) Conventional partial oxidation (POX) reaction - CH 4 + 1/2 O CO (exothermic; requires large oxygen plant) Membrane driven reforming - CH 4 + 1/2 O CO (exothermic; requires no oxygen plant; energy produced) Energy savings > 30% Cost reduction = 30-40% 11

12 Oxygen Flux in Mixed-conductors J O2 = RT 16F 2 L σ ln P O2 amb II P O2 I σ amb = σ i σ e σ i +σ e Oxygen flux is controlled by: ambipolar conductivity transference number chemical potential gradient thickness temperature surface exchange kinetics Examples: Perovskites (ABO 3 ) Brownmillerite (A 2 B 2 O 5 ) Pyrochlores (A 2 B 2 O 7 ) Fluorites (AO 2 ) 12

13 Methane conversion, CO and selectivities, and oxygen permeation in an SFC membrane reactor Conversion/Selectivity (mole %) Operated with reforming catalyst at 900 C (80% CH 4 /20% Ar feed, pressure 1atm) SrFeCo 0.5 O x Oxygen Flux (cm 3 (STP)/cm 2 -min) Time (days) 13

14 Air Products ITM Syngas is a Breakthrough Platform for Reducing the Cost of the Synthesis Gas Step in Hydrogen Production 14 (F. D. Sutterfield, NHA Mtg., April 29, 2004)

15 Flow diagram showing process for using dense ceramic membranes (OTM and HTM) to convert biogas to high-purity BioGas (CH 4 + CO 2 ) Air OTM Air Partial Oxidation Reaction Syngas ( + CO + CO 2 ) O O Water Gas-Shift Reaction CO 2 + HTM Hydrogen Separation Pure for fuel cells CO 2 for sequestration 15

16 Conventional Hydrogen Production from Biomass Gasification 16

17 Yes, my friends, I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable Water will be the coal of the future. Jules Verne, The Mysterious Island (1874) 17

18 Hydrogen Production from Water Using Mixed Conducting Ceramic Membranes Oxygen is removed by membrane. Non-galvanic (no electrodes/ electrical circuitry) High po 2 ( Production side) O O 2- Low po 2 (O 2 permeate side) e - O 2 Dense mixed (oxygen ion-electron) conductor ( C) O +1/2 O 2 Very low concentrations of and O 2 are generated even at relatively high temperatures (0.1 and 0.042% for and O 2, respectively, at 1600 C). Significant amounts of can be generated at moderate temperatures if the reaction is shifted toward dissociation by removing either O 2,, or both. U. Balachandran et al., Int. J. Hydrogen Energy, 29, 291, K = P P O2 P O

19 Production Rate Vs. p O (T = 900 C) Production Rate [cm 3 (STP)/min-cm 2 ] Thickness = 0.3 mm Oxy. Permeate side p = 0.8 atm Doped CeO 2 generation side O O - - e - O 2 consumption side /He O/He Production Rate (mol/s-cm 2 ) p O (atm) in oxidizing gas 19

20 Natural Gas-Assisted Water Dissociation Using Ceramic Membranes (O 2 consumption side = 5% methane/bal. N 2 ) produced on the CH 4 side = 0.64 cm 3 (STP)/min-cm 2 ) Production Rate (cm 3 /min-cm 2 ) Thickness = 0.58 mm Temperature = 900 C generation side O O - - e - ANL-1b O 2 consumption side CH 4 CO + 2 (2003 NHA) Production Rate (mol/s-cm 2 ) p O (atm) in oxidizing gas 20

21 Hydrogen Production from Water and Natural Gas Using Ceramic Membranes O CH 4 O -- Steam ( O) CO + 2 (exothermic) e - Methane (CH 4 ) + O O CO 2 for sequestration + O syngas CO, shift reactor CO 2, pure Hydrogen Pipeline O 21

22 Cost Analysis for Hydrogen Production Hydrogen Cost $8.00 $7.00 $6.00 $5.00 $4.00 $3.00 Production Cost Including comp, storage, dispensing $2.00 Steam Recirculated Water Generator Water Natural Gas Pressure Vessel Steam CO/ Shift Reactor $1.00 $ Delivery Capacity (kg/day) CO 2 CO 2 / Separator Analysis done by Jerry ANL / 0 Recirc Pump 0 / O Separator H Compressor 2 Storage 22

23 Proton Conductors Examples: SrCeO 3, BaCeO 3, Sr(Ba)ZrO 3, Complex perovskites A 2 B B O 6, nitrate-oxide P e - e - H + Wet H + + e - 1/2 1/2 H + + e - Potential Applications: Fuel cell separation/purification Electrolyzer Membrane reactor Sensor anode Proton conductor cathode (Prof. Truls Norby s talk on proton conductors for fuel cells & membranes) 23

24 Performance of BaCe 0.8 Y 0.2 O 3-δ Thin Films (10 µm) Hydrogen Pumping Characteristics of BCY Film (T=700 C, Wet 80% at Anode // N 2 at Cathode) Current-voltage curves Flux (cm 3 /min-cm 2 ) theoretical wet N2 dry N2 3.4 A/cm 700 C Cathode surface area: 0.5 cm Electrical Potential (V) dry wet 700 C anode gas: wet (p O = 0.03 atm/80% /He) OCV Current Density (A/cm 2 ) Current Density (A/cm 2 ) OCV = open circuit voltage 24

25 Single-Phase Mixed Conductor J H2 Dense Membranes for Hydrogen Separation Feed CO 2 CO etc. H + Low σ e- Low Flux ANL-0 e - = RT 4F 2 l σ ln p amb σ amb = σ σ H + e σ H + + σ e Poor Mechanical Integrity II p H2 I Mixed Conductor With Metal Feed CO 2 CO etc. Feed CO 2 CO etc. H + e - ANL-1 e - H + H + H / e - ANL-2 H / H + e - H2 J Structural Ceramic With Hydrogen Transport Metal Feed CO 2 CO etc. = AΦ l High Flux H ANL-3 H High Selectivity ( p feed p ) sweep H 2 Good Mechanical Integrity 25

26 Flux (ANL-3a) vs. Temperature Thickness 40 µm, Feed Gas: 100% at ambient pressure Flux (cm 3 /min-cm 2 ) Flux (scfh/ft 2 ) Temperature ( C) ANL-3a gives highest flux of self-supported HTMs. 26

27 Flux vs. p 1/2 Linear dependence of flux on p 1/2 shows flux is limited by bulk diffusion Extrapolation shows stand-alone ANL-3e HTM should yield flux >200 scfh/ft 2 at 900 C with feed gas at 300 psi. H 2 Flux (cm 3 /min-cm 2 ) 120 ANL-3e (Thickness - 22 µm) C C H 2 Flux (scfh/ft 2 ) p 1/ 2 p ( feed) p (sweep) Flux = AΦ l ( p feed p ) sweep H2 27

28 Nano-Structural Aspects of Transport in Electroceramics Point defects are very important for electroceramics Concentrations and mobilities are significantly changed at/or near interfaces Forms depletion, accumulation and inversion layers with respect to ionic and electronic carriers - cross-over from ionic to electronic conductivity in CeO 2 as a function of grain size Nano-Ionics References: 1) N. Sata, K. Eberman, and J. Maier (Max-Planck-Institut), Nature, 408, 946, Dec ) J. Maier, J. European Ceram. Soc., 24, 1251, 2004 Talks by Ole Martin Løvvik & Jan Swenson 28

29 Thickness-dependent electrical conductivity of YSZ thin films determined at different temperatures Ref: I. Kosacki, et al., Solid State Ionics 176 (2005)

30 Fundamental Research Needs Basis for ionic and electronic transport Phenomenological theory development Understanding the interfaces Rate limiting steps Single phase/multiphase mixture Crystal structure(s) Contribution of each phases (conductivities, transference numbers) Change in composition, structure, cell size, etc. during operation Chemical affinity Kinetics of absorption on surfaces 30

31 Research Needs and Challenges Long-term stability (of fluxes ---- deactivation) Compatibility of membranes with catalyst(s) Seals/manifolding for high pressures and temperatures Thermal cyclability of membrane seal Mechanical strength/durability to withstand high pressure and thermal cycling Reliable manufacturing techniques for membrane/module Cost System integration 31

32 Thank you! Thanks to The Research Council of Norway and The Birkeland Conference 32

33 Back-up slides/q&a/discussions 33

34 Electrolysis vs. Mixed-Conductors for Production Thermal efficiency of low-temperature electrolysis is 26-30% (75% efficiency with respect to electric energy input & thermal plant efficiency is 35-40%). e - O 2 O - - O e - P P e - e - CH 4 O - - O CH 4 O - - O e - In high-temperature solid oxide electrolyzer, most of the electric power is used in forcing oxygen through the electrolyte (overall efficiency of 39-44% for 38% efficiency of electric power generation). In NGASE, CH 4 is reacted with oxygen, reducing the chemical potential across electrolyte, thus minimizing the electricity consumption. Analysis of NGASE (LLNL, Int. J. Hyd. Energy 28, 483, 2003) shows a system efficiency of 70% with respect to primary energy. Use of mixed-conductor (present work) should further reduce the amount of energy consumption (non-galvanic) and therefore potential for higher system efficiency. 34

35 Estimated Cost of Production Using Membrane Technologies Natural gas reforming is 60% of production cost. (S. Lasher, et al., Technical Analysis, Proc DOE Program Review) Reforming cost could be reduced by 30-40% by using oxygen membranes. separation membranes could reduce purification cost by 30% relative to PSA. (S. Lasher, et al., Technical Analysis, Proc DOE Program Review) Estimated cost using combined oxygen and hydrogen transport membranes is $4/MM Btu or $0.55/kg. ( Production Facilities: Plant Performance and Cost Comparison, Final Report for Contract No. DE-AM26-99FT40465, Parsons) 35

36 Technical Goal and Objectives of U.S. DOE Hydrogen Program Goal: Research and develop low-cost, highly efficient hydrogen production technologies from diverse, domestic resources. Objectives: By 2010, reduce the cost of production from natural gas to $1.50/gge at the pump By 2015, reduce the cost of production fron biomassderived renewable liquids to $2.50/gge at the pump. By 2010, verify grid-connected electrolysis cost of $2.85/gge. By 2015, reduce the cost of production fron biomass to $1.60/gge at the plant gate By 2015, develop thermochemical/solar power processes to produce at a cost of $3/gge 36

37 Where are We with Fuel Cells Today? Cost: Today, many fuel cells cost about $3,000/kW Stationary power generation requires $800/kW Transportation requires $50/kW to compete with gasoline ICE Durability: Vehicles need >5,000 hr lifetime Primary stationary power needs 50,000 hr (Emergency power: only 5,000 hr) Today, the head of the pack is about halfway to both durability targets 37 (Gene McConnell, NHA Mtg., April 29, 2004)

38 Ceramic Membranes for Hydrogen Production Liquid fuels shift reaction CH 4 (natural gas, biogas) CO + (syngas) O 2- e - e - H + air Lean air Ceramic Membrane (Oxygen-ion & electron conductor) Ceramic Membrane (proton & electron conductor) Availability of a cheap source of high-purity hydrogen for fuel cells and other energy applications would maximize use of domestic fossil resources, ensure diverse energy sector, and address environmental concerns. ANL has developed a ceramic membrane that extracts hydrogen from natural gas. Ceramic membrane has demonstrated separation of hydrogen from gaseous mixtures in the temperature range of C. CO 2 for sequestration (clean fuel for fuel cells, power plants, transportation, coal liquefaction, etc.) Funded by DOE, Office of Fossil Energy 38

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40 Temperature-dependent oxygen permeation flux (Membrane thickness 0.75-mm) 10-4 SrFe-Co 0.5 O x 10 2 jo 2 (mol/s-cm 2 ) Reactor Cell jo 2 (cm 3 /min-cm 2 ) Temperature ( C) 40

41 Hydrogen Production Rates at 900 C vs. Inverse of Membrane Thickness Production Rate [cm 3 (STP)/min-cm 2 ] Production Rate (mol/s-cm 2 ) /Thickness (mm -1 ) 41

42 Dependence of Hydrogen Production Rate on Temperature 10 1 Production Rate (cm 3 /min-cm 2 ) 10 0 Thickness = 0.10 mm 700 C 600 C 500 C Production Rate (mol/s-cm 2 ) /T (K -1 ) 42

43 Natural Gas-Assisted Water Dissociation Using Ceramic Membranes 5 Production Rate (cm 3 /min-cm 2 ) mm, w/cat, wet 3% CH mm, w/o cat, dry 5% CH 4 Gd: CeO C Production Rate (mol/s-cm 2 ) p O (atm) on -generation side 43

44 Chemical Stability of ANL-3 Membranes Hydrogen Flux (cm 3 /min-cm 2 ) Feed gas: 61.3 %, 8.2% CH 4, 11.5% CO, 9.0% CO 2, 10% He 900 C Thickness 0.20-mm Hydrogen Flux (mol/s-cm 2 ) Hydrogen Flux (cm 3 /min-cm 2 ) Feed gas: same as (A) ppm S 900 C Thickness 0.20-mm Hydrogen Flux (mol/s-cm 2 ) Time (h) Time (h) (A) (B) 44

45 Chemical Stability of Cermet Membranes (0.2-mm-thick ANL-3e, Feed: 400 ppm S, 73% balance helium) Permeation Flux (cm 3 /min-cm 2 ) Time (h) 45

46 Microstructures of BCY Thin Films on Porous Support BaCe0.8Y0.2O3-δδ Fracture surface As-sintered top surface 46

47 0 H/Te H Comparison of Membranes Feed Gas: 4% H 2 in Ambient Pressure Membrane Thickness = 0.50 mm Flux (cm 3 /min-cm 2 ) ANL-1 ANL-2 ANL H 2 Flux (scfh/ft 2 ) Temperature ( C) ANL-3 HTMs give highest flux of ANL membranes. 47