ASEAN++ 2013 November 11-13, 2013, Chiang Mai University Hiraku Maruyama 1 *, Haruo Kishimoto 2 , Mana Yasui 1 , Teruhisa Horita 2 , Katsuhiko Yamaji 2 and Atsushi Yamazaki 1 1 Department of Earth Environmental Resource Engineering, Waseda University, Japan 2 National Institute of Advanced Industrial Science and Technology, Japan 1
Solid Oxide Fuel Cell (SOFC) Fuel Cell = power generator using O 2 and H 2 Fuel(100%) Fuel(100%) Power plant Fuel cell heat waste wire loss heat waste (20%) (5%) (55%) Heat Electricity Electricity (40%) (40%) (40%) Solid Oxide Fuel Cell(SOFC) ・ High total efficiency (~87%) ・ High output power ・ Easy gas reforming (CH 4 → H 2 ) http://www.chuden.co.jp/hekinan-pr/guide/facilities/thermalpower.html http://techon.nikkeibp.co.jp/article/WORD/20060418/116213/ http://www.osakagas.co.jp/company/press/pr_2010/1190846_2408.html
Solid Oxide Fuel Cell (SOFC) SOFC e - O 2- H 2 O O H 2 + O 2- ２ →H 2 O + 2e- electrolyte H 2 anode cathode (ceramics) Electrolyte performance = oxygen ion conductivity Higher temperature σ = qn μ (700~1000 ℃ ) is necessary σ : conductivity q : charge n :carrier concentration μ : carrier mobility
Apatite-type lanthanum silicate Reference: Welcome to Apatite Ionic Conductivity Home Page Fig. crystal structure of La 9.33 Si 6 O 26 Fig. conductivities of electrolyte[2] showing a unit cell[1] [YSZ: (ZrO 2 ) 0.91 (Y 2 O 3 ) 0.09 LSGM: (La 0.8 Sr 0.2 )(Ga 0.8 Mg 0.2 )O 3- α ] advantage La 9.33+ x Si 6 O 26+1.5 x ( x =0~0.67) 1. Higher ion conductivity ・ structure ≒ apatite [Ca 10 (PO 4 ) 6 O 2 ] 2. Lower temperature dependency ・ conductor : interstitial oxygen SOFC can be used ion ・ conduction path : c -axis at lower temperature Reference:[1] Welcome to Apatite Ionic Conductivity Home Page [2]Atsushi Mineshige et al, Effect of cation doping on ionic and electronic properties 4 for lanthanum silicate-based solid electrolytes, Solid State Ionics, 2011, Vol.192, pp.195 – 199
Purpose Improvement of oxygen ion conductivity σ = qn μ σ : conductivity q : charge n :carrier concentration μ : carrier mobility Mn +2 Sample : Mn +3 Mn +4 La 10- x Mn x (SiO 4 ) 6 O 3+ δ ( x =0.1~1.0) Mn +6 Mn +7 Ex.) La 3+ 10 (SiO 4 ) 6 O 3 La 3+ 9.0 Mn 4+ Mn 4+ 1.0 (SiO 4 ) 6 O 3.5 How does Mn influence the conductivity? 5
Solid state reaction method La 2 O 3 SiO 2 MnO 2 (planetary ball mill:250rpm,30min) Mix (powder,1400 ℃ ,10h) Calcine Fig. obtained pellet Grind (cold isostatic press:392MPa) Casted (1600 ℃ 10h) 4μm Heat Fig. SEM image of pellet’s surface (relative density:83-97%) Polish 6
Measurement method AC ・ Two-terminal method ８㎜ 1 ㎜ CE WE S RE ② Connect with the ① Pellets attached with Pt ③ Measure in the temperature 500 ～ 1000 ℃ electric wire mesh by Pt paste. Heated at （ in Air ） 1000 ℃ for 2h 7
Phase identification by XRD La 2 SiO 5 SiO 2 sample:La 10- x Mn x (SiO 4 ) 6 O 3+ δ x=1.0 No mark : apatite x=0.9 x=0.8 Intensity(a.u) x=0.7 Non-doped x=0.6 La 2 SiO 5 appear x=0.5 x=0.4 x=0.3 Mn doping x=0.2 La 2 SiO 5 disappear x=0.1 non-doped 15 20 25 30 35 40 CuK 2 /Degree Fig. XRD results of La 10- x Mn x (SiO 4 ) 6 O 3+ δ 8
Lattice constants change Shannon’s ionic radius( Å ) La > Mn Si > (1.03-) (0.67-0.90) (0.26-0.40) Fig. crystal structure of La 9.33 Si 6 O 26 showing a unit cell[1] smaller larger Lattice constant La 10 (Si 6- x Mn x ) O 26+δ (La 10- x Mn x ) Si 6 O 26+δ La 10 Si 6 O 27 9
Lattice constants change Sample:La 10- x Mn x (SiO 4 ) 6 O 3+ δ a ( =b ) c Fig. lattice constant a and c to the amount of Mn doped into La site 0.1~0.3 La site Mn Si site (La 10-x Mn x )[Si 6-y Mn y ]O 26+δ 0.3~1.0 La site [ x+y= 0.1~1.0] Mn Si site 10
Conductivity Sample : La 10- x Mn x (SiO 4 ) 6 O 3+ δ 0.1 × 10 Non-doped Fig. Arrhenius plot of La 10- x Mn x (SiO 4 ) 6 O 3+ δ 11
Discussion σ = qnμ Carrier (O 2- ) mobility The number of Carrier （ O 2- ) σ : conductivity q : charge Phase purity n :carrier concentration μ : carrier mobility La site : Mn 2+ Si site: Mn 3+ [2] (La 3+ 10- x Mn 2+ La 3+ x )Si 6 O 3- x /2 10 Si 6 O 27 Mn 2+ La 10 Si 4+ 6 O 27 La 3+ 10 (Si 4+ 6 -y Mn 3+ Mn 3+ y )O 3- y /2 Carrier concentration Conductivity Mn doping (O 2- ) decrease decrease [2] Julian R. Tolchard, Peter R. Slater, and M. Saiful Islam (2007), Insight into Doping Effects in Apatite Silicate Ionic Conductors, Adv.Funct.Mater , 2007, Vol.17, pp.2564-2571 12
Discussion 1073K Fig. conductivities as the function of x + y at 1073K (La 10- x Mn x )(Si 6-y Mn y )O 26+ δ Carrier mobility Si substitution Conductivity ⇒ carrier mobility improved enhanced Phase purity ⇒ conductivity improved (La 2 SiO 5 disappeared) Ex) La 9.83 (Si 4.5 Al 1.5 )O 26 [3] [3] E. J. Abram, D.C.Sinclair and A. R. West (2001), A novel enhancement of ionic conductivity in the cation-deficient apatite 13 La 9.33 (SiO 4 ) 6 O 2 , J.Mater. Chem. , 2001, Vol.11, 1978 – 1979
Discussion 1073K Fig. conductivities as the function of x + y at 1073K (La 10- x Mn x )(Si 6-y Mn y )O 26+ δ Carrier(O 2- ) Conductivity x + y =0.1: (La 10-x Mn x )(Si 6-y Mn y )O 26.95 concentration decreased x + y =1.0: (La 10-x Mn x )(Si 6-y Mn y )O 26.50 14
Conclusion ① Co-exist phases like La 2 SiO 5 which appeared in La 10 Si 6 O 26+ δ were not observed in La 10- x Mn x Si 6 O 26+ δ . ② The structure formula of Mn-doped lanthanum silicate was (La 10- x Mn x )[Si 6- y Mn y ]O 26+δ . ③ The sample of x = 0.1 showed the highest conductivity in this examine. ④ Conductivity of Mn-doped lanthanum silicate is affected by the amount and distribution of Mn. 15
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