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1 Korea Institute of Energy Research

Electrochemical synthesis of ammonia from steam and nitrogen using an oxygen-ion conducting electrolyte. Jong Hoon Joo , Hyung Chul Yoon, Hana Jeoung, Ji Haeng Yu, Jong-Nam Kim, Young Min Woo, Jin Young Jang.

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1 Korea Institute of Energy Research

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  1. Electrochemical synthesis of ammonia from steam and nitrogen using an oxygen-ion conducting electrolyte Jong Hoon Joo, Hyung Chul Yoon, Hana Jeoung, Ji Haeng Yu, Jong-Nam Kim, Young Min Woo, Jin Young Jang KoreaInstituteofEnergy Research(KIER), Daejeon,SouthKorea 1 Korea Institute of Energy Research

  2. Overview • Hydrogen manufacturing by Solid Oxide Electrolysis Cells (SOECs) • Ammonia manufacturing by Solid Oxide Electrolysis Cells (SOECs) • Electrochemical synthesis of ammonia from steam and nitrogen using an oxygen-ion conducting electrolyte KoreaInstituteofEnergy Research

  3. Introduction SOECs SOFCs Fuel(H2) Steamrich + H2 O2 Air(O2) H2O H2rich +Steam, SolidOxide FuelCells(SOFCs) SolidOxideElectrolysisCells(SOECs) Anode RXN Cathode RXN Overall RXN H2O + 2e- → H2 + O2- O2- → ½O2 +2e- H2O → H2 + ½O2 Endothermic (ΔH < 0) H2 + O2- → H2O + 2e- ½O2 + 2e- → O2- H2 + ½O2 → H2O Exothermic (ΔH > 0) Reactionheat KoreaInstituteofEnergy Research

  4. Thermodynamicaspects ► Energy requirements for electrolysis SOEC operating temp. (600-1000oC) Steam electrolysis ? Why??? ∆G= ∆ H-T ∆ S • S. Herring (INL), 2005 Hydrogen, Fuel Cells & Infrastructure Technologies Program Review • ▫ Overall thermal-to-hydrogen efficiency > 50% • ▫ Electrical energy requirements for electrolysis < • HTE:~34kWh/kg Conventional:~50kWh/kg KoreaInstituteofEnergy Research

  5. Oxygenionconductingelectrolyte - ElectrolyteMaterialsforSOFC/SOEC 900 800 700 600(oC) ElectricalConductivity(S/cm) ScSZ(Scandiastabilizedzirconia) 0.1 YSZ (Yttriastabilizedzirconia) 0.01 0.8 0.9 1.0 1000/T(K-1) 1.1 1.2 [1] B.C.H. Steele,Nature414(2001)345 KoreaInstituteofEnergy Research

  6. Buttoncell tests LSM LSM-YSZ YSZ NiO-YSZ • ▫ Button cell • active area: 0.5 ~ 1.0 cm2 • cell thickness: 1 mm • sealing materials: Pyrex Buttoncelltestunit KoreaInstituteofEnergy Research

  7. Buttoncell tests(SOEC) 1.5 YSZ (850oC) ScSZ (850oC) ScSZ (800oC) ScSZ (650 C) o CellVoltage/V 1.0 0.5 SOEC mode SOFCmode 50%HO 2 0.0 -1 0 1 CurrentDensity/Acm-2 2 Polarizationresistance:SOECmode>SOFCmode Korea Institute of Energy Research 7

  8. Current-voltagecharacteristics ► Button cell I-V tests From Faraday’slaw, Hydrogenproductionrate is 𝐼�𝑚𝐻2 �̇ = 𝑛� 3 −1 ≅ 1 𝐶∙ 𝑠𝑠𝑠−1 × 22400 𝑠𝑚 ∙ 𝑚𝑚� �̇ SOFCmode 2 × 96485 𝐶∙ 𝑚𝑚�−1 SOEC mode = 0.116 𝑠𝑚3 ∙ 𝑠𝑠𝑠−1 𝑚≅ 0.116 × � 𝐼𝑑𝑑 ▫ Hydrogen production rate : 8.3 cc/min∙cm2 ▫ Over 30% steam content is required. @1.3V (~ 100%currentefficiency) KoreaInstituteofEnergy Research

  9. Operationconditions ► Button cell operating conditions • ▫ I-V results: • High steam content high performance • No significant differences in H2 production rate with steam content at low temp • ▫ Impedance results: • Resistances decrease with temperature. • Rc - strong dependence on steam content • Rohm – no connection with steam content KoreaInstituteofEnergy Research

  10. Stackdesign • Manifold glass sealing • H2O (rich) + H2 (lean) • Stack structures • H2O (lean) + H2 (rich) • ▫ Characteristics of KIER flat-tubular cell stack • All-ceramic stack (ceramic interconnector all-in-one) • Highmechanicalstrength • Minimumsealingareaandmanifold • Minimumstackvolume • Enhancedactivearea KoreaInstituteofEnergy Research

  11. Processing Extrusion Machinework Dip-coating Spray-coating Sintering Manufacturingstep Flat-tubularsinglecells Stackmodule KoreaInstituteofEnergy Research

  12. Stackdevelopment • Stackdevelopment KoreaInstituteofEnergy Research

  13. Ammoniaasanenergycarrier • While the introduction of a hydrogen economy has its merits, the associated problems with on-board hydrogen storage are still a barrier to realization. • Ammonia and related chemicals can provide an alternative energy vector. -Haber-Boschprocess(250bar, 450oC) N2(g) +3H2 (g)2NH3 (g) Energyconsumption:36.GJ/ton NH3 -Solid-stateelectrochemicalprocess(1bar,300-700oC) 3H2O(g) + N2(g)2NH3 +3/2O2(g) 26GJ/ton NH3 Overallcostreduction:1/2ofthecurrentpriceofNH3 [2] [2]J.Holbrook,Ammonia:ThePromiseofGreenFuel, Spring2008 KoreaInstituteofEnergy Research

  14. Energydensity Fig.1. Volumetricversusgravimetricenergydensityofthemostimportantenergycarriers [3] -Onlyammoniaandhydridesexhibitanenergydensityclosetofossilfuelssuchas coalandoil,muchhigherthancompressedhydrogen. KoreaInstituteofEnergy Research [3]A.Zutteletal.,Philos.Trans.R Soc.A-Math Phys.Eng. Sci.(2010)

  15. SolidStateAmmoniaSynthesis • SolidStateAmmoniaSynthesis(SSAS)using H2andN2 • H2 • e- H+ Proton conductor N2 NH3 • Proton conductor electrolyte • Perovskite: SrCeO3, BaZrO3, CaZrO3, BaCeO3, SrZrO3 et al. Pyrochlore: La2Zr2O7, La2Ce2O7 et al. Polymer:Nafionetal. KoreaInstituteofEnergy Research

  16. SolidStateAmmonia Synthesis usingH2 and N2 • SummaryoftheSSASusingH2 andN2 [4]A.Ibrahimet al.,J.SolidStateElectrochem.(2011) KoreaInstituteofEnergy Research

  17. SolidStateAmmonia Synthesis usingH2O and N2 • Usingsteaminsteadofhydrogencost saving(productionandpurification) • Oxygenionconductor 2.Proton conductor Air H2O e- e- H+ O2- N2 2NH3 3H2O 6H+ +3/2O2 + 6e- - Drawbacks of proton conducting oxides: High sintering temp. (BaZrO3 ~ 1700 oC) Formation of secondary phases (phase instability) High grain boundary resistance 3H2O+N2 3O2- 3/2O2+6e- 2NH3 3H2O+N2 +6e-3O2-+2NH3 KoreaInstituteofEnergy Research

  18. Experimental e- Electrodes: Pt or (LSF)La0.6Sr0.4FeO3-(GDC)Ce0.9Gd0.1O2-δ Electrolyte : O2- ion conductor (3YSZ, t: 90 ㎛) O2- NH3 +H2O+N2 +H2 H2O+N2 Overallcellreaction:3H2O+N2 2NH3 + 3/2O2 - N2 (50cc/min) +3%H2O - Electrodearea:1cm2 - Measuringtemperature:500-660oC • Electrochemicaltest • Current-voltagecharacteristic • Impedancespectroscopy KoreaInstituteofEnergy Research

  19. Analysisofammoniaformation • IndophenolBlueMethod • Phenol:1ml • Sodiumnitroprusside:1ml • Alkalinecitrate+Sodiumhypochlorite:2.5ml • Ammoniacollectionquantifiedbybubblingthroughsolution. • Analyzedbyspectrophotometer Standard Curve 1.474 Range:0.01-1.5mg/L :0.01-10ppm 1.000 Abs. 0.500 Error: ±0.013 mg/L (95% confidence level) 0.000 -0.134 0.000 0.500 y = 0.89441 x + 0.00000 Correlation Coef f icient r2 = 0.99929 Multiple Correlation Coef f icient r2 = 0.99929 1.000 1.500 Conc.(mg/l) KoreaInstituteofEnergy Research

  20. Mixedconductingperovskite • Mixed ionic electronic conductor • Mixed conducting perovskites contain alkaline earth and rare earth cations on the A-site and a transition metal on the B-site. • For examples, La0.6Sr0.4CoO3-δ has a high ionic conductivity (≈ • 0.1 S/cm , δ ≈ 0.1 at 800 oC in 1 atm O2) caused by oxygen vacancy. <Idealcubicperovskitestructure> KoreaInstituteofEnergy Research

  21. Mixedconductingperovskite • ElectrodeReactions - Electronicconductor: Pt - Mixed conductor : (La,Sr)FeO3-δ • Three-phase boundary (gas, electron,ion) area in electrodes is important for the oxygen ion transport. • Polarization resistance: Pt > Mixed conducting perovskite KoreaInstituteofEnergy Research

  22. ImpedancespectraatOCV 200 660oC Pt electrodes 150 12Hz -Z''(Ω) 100 50 0.8Hz LSF-GDCelectrodes 0 0 50 100 150 200 250 Z'(Ω) 300 350 400 • Anode:air • Cathode:N2 (50cc/min) + 3%H2O KoreaInstituteofEnergy Research

  23. Current-voltagecharacteristics 1.0 1.0 660oC 660oC 0.8 0.8 Voltage(V) Voltage(V) 0.6 0.6 0.4 0.4 0.2 0.2 Pt electrodes LSF-GDCelectrodes 0.0 0.0 - LSF-GDC electrodeHighercurrentcanbeapplied. KoreaInstituteofEnergy Research

  24. Current-voltagecharacteristics 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 o o 500 C 500 C Voltage(V) Voltage(V) Pt electrode LSF-GDCelectrode - LSF- GDC electrode80timeshighercurrentthan Pt at500oC KoreaInstituteofEnergy Research

  25. Dependenceofammoniaproductionrateontheappliedcurrent 660oC 660oC 2.0x10-10 2.0x10-10 Ammoniasynthesisrate(mol/sec) Ammoniasynthesisrate(mol/sec) LSF-GDCelectrode Pt electrode 1.5x10-10 1.5x10-10 1.0x10-10 1.0x10-10 5.0x10-11 5.0x10-11 • 0.0 0.0 • 0.0 0.1 0.2 0.3 0.4 0.5 0.6 • Current (mA) • Ammonia production rate • - Pt-YSZ-Pt 1.2ⅹ 10-10 mol/cm2∙sec at 660 oC 0 2 4 6 Current(mA) 8 10 - LSF-GDC/YSZ/LSF-GDC 1.7ⅹ 10-10 mol/cm2∙sec at 660 oC • Pd-SCY-Ru 9.1ⅹ 10-14 mol/cm2∙sec • Pt-Nafion-Ru 2.1ⅹ 10-11 mol/cm2∙sec • [5] A. Skodra et al., Solid State Ionics (2009) [6] V. Kordali et al., Chem. Commun. (2000) at650oC[5] at90oC[6] Thereareonlytwoliteraturedata(usingH2OandN2) KoreaInstituteofEnergy Research

  26. Dependenceofammoniaproductionrateontheappliedcurrent • Ammonia production rate • - Pt-YSZ-Pt 1.2ⅹ 10-10 mol/cm2∙sec at 0.4 mA • Theoretical value (Faraday’s law ) : 1.4ⅹ 10-9 mol/cm2∙sec at 0.4 mA 𝑚𝑚�𝑚𝑚𝑚𝑚�𝑣𝑚𝑣𝑚𝑚� ≈ 8.6% 𝑡𝑡𝑚𝑡𝑚𝑚𝑡𝑡𝑡𝑚𝑣𝑣𝑚𝑣𝑚𝑚� - LSF-GDC/YSZ/LSF-GDC 1.7ⅹ 10-10 mol/cm2∙sec at 9 mA Theoretical value: 3.1ⅹ 10-8 mol/cm2∙sec at 9 mA 𝑚𝑚�𝑚𝑚𝑚𝑚� 𝑣𝑚𝑣𝑚𝑚� 𝑡𝑡𝑚𝑡𝑚𝑚𝑡𝑡𝑡𝑚𝑣𝑣𝑚𝑣𝑚𝑚� ≈0.6% • Conversionrateshouldbe increased. KoreaInstituteofEnergy Research

  27. Conclusions • Ammonia is synthesized from steam and nitrogen by using oxygen ion conducting electrolyte. • The maximum rate of ammonia production is 1.7ⅹ 10-10 mol/cm2∙sec with perovskite electrode. • about 2000 times larger than reported value (Pd-SCY-Ru) • about 10 times larger than reported value (Pt-Nafion-Ru) • Further study is necessary to enhance the ammonia formation rate. • - Reaction mechanism (N2 dissociation et al.) • - Factors affecting the rate of ammonia formation (temperature, catalysis, conductivity) KoreaInstituteofEnergy Research

  28. Thankyouforyourattention!! KoreaInstituteofEnergy Research

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