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D09.06.12.presentation D09.06.12.presentation Presentation Transcript

  • Intermediate-temperature steam electrolysis using proton-conducting perovskite Hiroshige Matsumoto, Takaaki Sakai, Shotaro Matsushita, Tatsumi Ishihara Environmental Technology Reserch Div. INAMORI Frontier Research Center & Department of Applied Chemistry, Faculty of Engineering, Kyushu University International Workshop on High Temperature Water Electrolysis Limiting Factors 09-10 June, 2009 Hotel Renaissance Karlsruhe, Germany
  • Proton conducting electrolyte for SOEC Oxide ion conductor Proton conductor Anode Cathode Anode Cathode O2- H2O H2O H+ O2 H2 H2 O2 e- D.C. power e e- D.C. power e - - source source When the proton conductor is used for SOEC, Steam should be introduced to the anode: = No separation is needed for hydrogen/steam. 2
  • Proton conductor for IT use N. Ito, M. Iijima, K. Kimura and S. Iguchi, Journal of Power Sources 152 (2005), p. 200. BaCe0.9Y0.1O3-| YSZ σ 2007/3/26 3 3
  • Outline of this work SOEC using proton-conducting oxide electrolyte has been investigated. • Electroyte: SrZrO3-based proton conductor. • Electrode materials and structures were examined for the anode and cathode. • Thin film electrolyte cell was tested for better efficiency. 4
  • Proton formation in oxide SrZrO3 Partial substitution of Y3+ for Zr4+ SrZr0.9Y0.1O2.95 0.05 H2O SrZr0.9Y0.1H0.1O3 5
  • Proton formation in oxide H H H H Defect equilibriums H2O+VO =2H++OO O2+VO =2h++OO H2+2h+=2H+ 6
  • Why strontium zirconate ? Cerates are more conductive Platinum electrode is much than zirconates. more active for cerates than Temperature / oC 1000 900 800 700 600 for zirconates. 10-1 1.0E-1 1200 BaC e Cathodic (b) 0.8 Y0.2 O 3-α 800 ηRC / mV BaCe 0.9 Nd0 O SrZr0.9Y0.1O3-α .1 3-α 400 SrCe0.85Yb0.05O3-α 1.0E-2 10-2 Conductivity / S cm-1 SrC 0 e0. 1200 95 Yb 0 Anodic .05 O3 -α 800 ηRA / mV SrZ r0.9 Y 5 0 .05 O3 1.0E-3 10-3 -α 400 CaZ 0 La r 0 0.9 In 0 100 200 300 400 -2 500 600 .9 Ca 0 .1 O3 0 .1 Sc -α Current density / mA cm O 3- α Electrode overpotentials during 10-4 1.0E-4 0.7 0.8 0.9 1.0 1.1 1.2 hydrogen pumping at 800C 1000 K / T 7
  • However, cerate is not so stable. Standard free energy changes for: SrMO3 [s] + H2O[g] = Sr(OH)2 [s] + MO2[s] SrMO3 [s] + CO2[g] = SrCO3 [s] + MO2 [s] 200 100 150 50 100 -1 -1 ΔG / kJ mol ΔG / kJ mol 0 50 -50 o o 0 -100 -50 -150 -100 -200 200 400 600 800 1000 1200 200 400 600 800 1000 1200 o o Temperature / C Temperature / C Cerate is reactive with CO2 and even with steam at lower temps. 8
  • Sr(Zr,Ce)0.9Y0.1O3 Ryu & Haile (1999) Ba(Ce,Zr)O3 Katahira (2000) Ba(Ce,Zr)O3 Irvine (2006) Ba(Ce,Zr,Y,Zn)O3 o temperature / C We chose -1 900 800 700 600 500 400 Sr(Zr,Ce)0.9Y0.1O3 (S cm )} -1 -2 SrZr 0.5Ce0.4Y0.1O3-α 4 x 10-3 S/cm log{ -3 1 x 10-3 S/cm SrZr0.9Y0.1O3-α -4 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 3 10 K/T 9
  • Materials for electrode and electrolyte SrZr0.9Y0.1O3-α (SZY-91), SrZr0.5Ce0.4Y0.1O3-a (SZCY-541) electrolyte Solid-state reaction method Electrolyte calcined at 1350ºC for 10 hrs in air, CIP at 300 MPa and sintered at 1700ºC for 10 hrs Interlayer Anode: Sr0.5Sm0.5CoO3 (SSC) SSC paste was screen-printed and fired at 950oC Electrode for 30 min in situ. Sample Cathode: Ni NiO paste was screen-printed and fired at 950oC Electrolyte Anode for 30 min in situ, and was reduced under 1%H2 gas atmosphere at 600oC SrCe0.95Yb0.05O3(SCYb) interlayer Interlayer SCYb paste was screen-printed and fired at 1500oC for 6 hrs Cathode Platinum electrode (anode or cathode) Pt pasted was screen-printed on the sample and fired at 950oC for 30 min in situ. 10
  • Experimental apparatus Glass packing Gas flow : Anode gas o Anode 1%O2-Ar gas humidified at 81 C (50%H2O) Cathode gas Reference 1%H2-Ar gas humidified at 17oC Cathode Electrode performance : Current interruption method Pt wire × 2 Pt wire × 2 H2 evolution rate : Gas chromatography Anode gas ProboStatTM ProboStatTM Cathode gas 11
  • Anodes: Sr0.5Sm0.5CoO3 (SSC) vs. Pt Anode overpotential H2 evolution rate -2 1.5 H2 evolution rate / mol min cm -5 2.0x10 -1 800oC 800oC Voltage / V 1.0 -5 1.0x10 0.5 0.0 0.0 0 25 50 0 25 50 Current density / mA cm-2 Current density / mA cm-2 : Pt | SZY-91|Pt Pt anode also showed poor performance Two problems (1)High overpotential (2)Low current efficiency
  • Anodes: Sr0.5Sm0.5CoO3 (SSC) vs. Pt Anode overpotential H2 evolution rate -2 1.5 H2 evolution rate / mol min cm -5 2.0x10 -1 800oC 800oC Voltage / V 1.0 -5 1.0x10 0.5 0.0 0.0 0 25 50 0 25 50 Current density / mA cm-2 Current density / mA cm-2 : SSC | SZY-91|Pt : Pt | SZY-91|Pt Pt anode also showed poor performance SSC anode showed good performance more than Pt anode Oxide electrode can work well as electrode of an electrochemical cell using protonic conductors 13
  • Cathodes: Porous Ni Cathode overpotential H2 evolution rate -4 -2 1.5 1.0x10 H2 evolution rate / mol min cm -1 800oC 800oC Voltage / V 1.0 -5 5.0x10 0.5 0.0 0.0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Current density / mA cm-2 Current density / mA cm-2 : SSC | SZY-91|Ni The cathode overpotential of the SCYb interlayer cell was significantly lower than that of the non-interlayer cell Compatibility to metal electrode : SrCeO3 >> SrZrO3 ? 14
  • Sample Cathodes: SrCe0.95Yb0.05O3 interlayer Electrolyte Anode Cathode overpotential H2 evolution rate -4 -2 1.5 1.0x10 H2 evolution rate / mol min cm Interlayer -1 800oC 800oC Cathode Voltage / V 1.0 -5 5.0x10 0.5 0.0 0.0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Current density / mA cm-2 Current density / mA cm-2 : SSC | SZY-91|SCYb/Ni : SSC | SZY-91|Ni The cathode overpotential of the SCYb interlayer cell was significantly lower than that of the non-interlayer cell Compatibility to metal electrode : SrCeO3 >> SrZrO3 ? 15
  • Electrolyte: SrZr0.9Y0.1O3 SrZr0.5Ce0.4Y0.1O3 Anode overpotential Cathode overpotential 0.6 800oC 2 800oC Voltage / V 0.4 Voltage / V 1 0.2 0.0 0 0 100 200 300 400 0 100 200 300 400 : SSC | SZY-91|SCYb/Ni : SSC | SZY-91|Ni The improvement by the partial replacement was observed only in the case of non SCYb interlayer cell at 800oC. With regards to the overpotentials, the effect of the partial replacement is limited 16
  • Electrolyte: SrZr0.9Y0.1O3 SrZr0.5Ce0.4Y0.1O3 Anode overpotential Cathode overpotential 0.6 800oC 2 800oC Voltage / V 0.4 Voltage / V 1 0.2 0.0 0 0 100 200 300 400 0 100 200 300 400 : SSC | SZCY-541|SCYb/Ni : SSC | SZCY-541|Ni : SSC | SZY-91|SCYb/Ni : SSC | SZY-91|Ni The improvement by the partial replacement was observed only in the case of non SCYb interlayer cell at 800oC. With regards to the overpotentials, the effect of the partial replacement is limited 17
  • Electrolyte: SrZr0.9Y0.1O3 SrZr0.5Ce0.4Y0.1O3 -2 H2 evolution rate / mol min cm -4 1.5x10 -1 800oC -4 1.0x10 : SSC | SZY-91|SCYb/Ni 5.0x10 -5 : SSC | SZY-91|Ni 0.0 0 100 200 300 400 500 -2 Current density / mA cm The hydrogen evolution rates were enhanced by the partial replacement in both cases The partial replacement of Zr with Ce is effective for enhancing the ionic transport (reducing the electronic current) The hydrogen evolution rate of the SSC|SZCY-541|SCYb/Ni cell showed almost the same value as the theoretical one up to 100 mA cm-2. 18
  • Electrolyte: SrZr0.9Y0.1O3 SrZr0.5Ce0.4Y0.1O3 -2 H2 evolution rate / mol min cm -4 1.5x10 -1 800oC -4 : SSC | SZCY-541|SCYb/Ni 1.0x10 : SSC | SZCY-541|Ni : SSC | SZY-91|SCYb/Ni 5.0x10 -5 : SSC | SZY-91|Ni 0.0 0 100 200 300 400 500 -2 Current density / mA cm The hydrogen evolution rates were enhanced by the partial replacement in both cases The partial replacement of Zr with Ce is effective for enhancing the ionic transport (reducing the electronic current) The hydrogen evolution rate of the SSC|SZCY-541|SCYb/Ni cell showed almost the same value as the theoretical one up to 100 mA cm-2. 19
  • Thin film electrolyte cell Ni/SZCY541 cermet Slurry coating of SZCY541 Post annealing in hydrogen 20
  • Thin film electrolyte cell -2 1%O2-Ar,anode|electrolyte|cathode,1%H2-Ar Hydrogen evolution rate / mol min cm -5 5.0x10 o 600 C -1 SSC55|SZCY541(film 22μm)|Ni/SZCY541(RUN72) 1%O2-Ar,anode|electrolyte|cathode,1%H2-Ar -5 4.0x10 SSC55|SZCY541(0.5mm)|SCYb_Ni(RUN51) 3 o (50% H2O electrolysis) 600 C IV Theoretical SSC55|SZCY541(film 22μm)|Ni/SZCY541(RUN72) -5 3.0x10 SSC55|SZCY541(0.5mm)|SCYb_Ni(RUN51) -5 (50% H2O electrolysis) 2.0x10 -5 2 1.0x10 Voltage / V 1.2V@0.1A/cm2 0.0 0 50 100 150 -2 Current density / mA cm 1 Translation to 100%H2 production: 0 1.4 V at 0.1 A/cm2 0 50 100 150 -2 Current density / mA cm 21
  • Summary Electrolyte : SrZr0.5Ce0.4Y0.1O3-a (SZCY-541) In the case of SrZrO3-based hydrogen pumps, the partial replacement of Zr with Ce was effective to decrease the electrode overpotential. Anode : Sr0.5Sm0.5CoO3-a (SSC) One of the typical oxide electrodes, having an e- conductivity of around 103 S cm-1 and used for air electrodes of SOFCs Cathode : Ni Having a catalytic activity with respect to hydrogen and is used for fuel electrodes in SOFCs Cathode/electrolyte interface : SrCe0.95Yb0.5O3-a (SCYb) SrCeO3-based electrolytes have a better compatibility with metal electrodes Cathode-supporting thin filme electrolyte Slurry coating method to fabricate 22 m thick dense electrolyte membrane 1.4 V at 0.1A/cm2 for 100%H2 production 22
  • A nanoionics in proton-conducting oxide -2.0 800oC -2.5 -3.0 SrZr0.9Y0.1O3-α SrZr0.9Y0.1O3-α -3.5 log(σ/Scm ) -1 nitrate method -4.0 Pt/SrZr0.9Y0.1O3-α composite -4.5 Nitrate method(Pt 4vol%) -5.0 Sinter of powder mixture (4vol%) -5.5 -6.0 -25 -20 -15 -10 -5 0 Pt nanoparticles log(p(O2)/atm) (a) Defect equiliburia conduction band Nonoionics H2O+VO =2H++OO Effect ? hole EF O2+VO =2h++OO H2+2h+=2H+ metal valence band oxide (electrolyte) Effect of Nano-Size Platinum Dispersion on the Proton-Conducting Properties of SrZrO3- 23 based Oxide October 16, 2008, PRIME2008, Honolulu, HI. USA
  • Effect of Thickness of SSC anode 50%H2O, SSC |SZCY-541| 5Yb-SCO_Ni, 1%H2 -2 o Hydrogen evolution rate / mol min cm 600 C SSC thickness (μm) -1 -4 1.5x10 3.5 34 17 54 -4 20 Theoretical 1.0x10 -5 5.0x10 0.0 0 100 200 300 400 -2 500 600 Current density / mA cm 24