Atomic Layer Deposition, a rising technique for SOFC and MCFC devices

Transcription

1 Atomic Layer Deposition, a rising technique for SOFC and MCFC devices A. Meléndez-Ceballos, D. Chery, A. Marizy, V. Albin, A. Ringuedé, M. Cassir* * Head Laboratoire d Electrochimie, Chimie des Interfaces et Modélisation pour l Energie, LECIME, UMR 7575 CNRS, ENSCP, Paris, France

2 High temperature fuel cells & electrolysis 1 2 MCFC: C O CO 2 e - CO MCFC/SOFC Composite carbonate/oxide SOFC: C 1 2 O + _ 2 e O 2-2 CO 3 2- NiO Li 2 CO 3 - K 2 CO 3 Ni + 2 à 10% Cr ou Al 2 - H + CO H O + CO + 2 e lifetime & performance: Nanostruct./electrochem. half-cells single cells La 1-x Sr x MnO 3 O 2- ZrO 2 -Y 2 O 3 O 2- Cermet Ni-YSZ _ + O 2 - H O 2 e 2 2 H + 1 FC H2 + O2 H2O 2 SOEC

3 Nano-scaled layers for SOFC, i.e. CeO 2 or ZrO 2 -based * As SOFC electrolytes: µ-sofc Charge transfer enhancement, resistance conductivity? * Interfacial layers Chemical diffusion barrier (cathode/electrolyte interface) Electronic barrier (anode/electrolyte interface) Catalyst/electrode (at both interfaces) Bond layer * As corrosion protective layers for interconnects * As active layer at the cathode interface Electrode catalysts Interconnect Anode (thick or thin) Electrolyte (thick or thin) Cathode (thick or thin) Interconnect Protective layer Electronic barrier Ionic diffusion barrier Protective layer

4 Surface saturation reaction. Thickness: from few nm to µm Atomic layer Deposition Growth speed ALD window Deposition T - Crystaline as deposited M. Cassir et al., J. Mater. Chem., 20 (2010) 8987 R. Puurunen, J. Appl. Phys., 97 (2005)

5 Litterature orientations Two main tendencies / use of ALD in SOFCs applications: Ø Low operating temperatures (<500 C) for micro systems such as portable applications. In µ-sofcs, ultrathin electrolyte layers have a significant role and ALD presents a serious advantage. ü The use of ultrathin catalytic or current-collector layers of Pt and Pt grid-patterned catalysts is common. ü However, this approach supposes the direct use of hydrogen and contradicts the requirements of SOFCs in cogeneration: avoiding precious metals and using fuels as natural gas or biomass which implies a reforming process operating at around 600 C. Ø The second tendency concerns electrolyte or catalysts interlayers and / or cheaper electrode materials activated by ultrathin ALDprocessed materials.

6 State-of-the-Art Electrolyte, interfaces & current collectors: (i) Stabilized zirconia (e.g. YSZ): ZrO 2, YSZ, ZrO 2 -In 2 O 3 from few nm to 1 µm. on planar substrates, on porous electrodes and on pre-patterned surfaces (ii) Ceria and doped ceria (e.g. Gd 0.2 Ce 0.8 O 2-d = GDC), YDC (iii) LaGaO 3, which is a potential electrolyte when doped: LSGM (La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 ) (iv) BaZrO 3, proton-conductor (v) Pt deposits (catalysts or/and current collectors) Cathode: a) La x Sr 1-x MnO 3 (LSM) b) La 1-x Ca x MnO 3 : potential electrode c) La 1-x Sr x FeO 3 (LSF) Anode: LaGaO 3 -based materials when doped with Sr and Mg Main teams: Prinz et al., Mc Intyre et al., Bent et al. (Standford), Niinistö et al (Helsinki), Cassir et al. (Paris), Nilsen et al. (Norway), Review Input of Atomic Layer Deposition for Solid Oxide Fuel Cell Applications, M. Cassir, A. Ringuedé, L. Ninistö, J. Mater. Chem., 20 (2010) 8987

7 Ø Enhanced oxygen exchange on surface- engineered YSZ* 10 nm of ALD- processed YSZ (14 mol. % Y) on YSZ single- crystal YSZ O 2 surface exchange coefficient 5 fold increase (Isotopic oxygen exchange tests + SIMS) Ø Enhancing O 2- incorpora/on kine/cs by nanoscaled interlayers**, *** 17.5 nm of YDC (14.1 mol. % Y) between YSZ and a porous Pt cathode enhances the performance of LT- SOFC cathode/electrolyte R while increasing the exchange j 0 by a factor of 4 at C Enhancement of the performance of the cell x 3 * Chao et al., ACS Nano, 7 (2013) 2186 ** Fan et al., Nanole:ers, 11 (2011) *** Fan et al., J. Mater. Chem., 21, (2011).

8 Ø Y- doped BaZrO 3 proton conduc/ng membranes (BYZ) of 100 nm used in a single cell with Pt porous electrodes* 100 nm thin films: ü ALD- processed: 136 mw/cm² at 400 C ü PLD (pulsed laser deposi?on)- processed : 120 mw/cm² at 450 C Ø Proton conduc/on- based fuel cell with YSZ electrolyte by ALD** Grain sizes of nm result in a high density of grain boundaries, which together with the OH - incorpora?on tend to provoke the proton conduc?vity of the YSZ thin film (200 nm) 10 mw/cm² at 450 C * Prinz et al., Chem. of Mater. 21, 3290 (2009) ** J. S. Park et al., Chem. Of Mater., 22, 5366 (2010)

9 ZrO 2 -Y 2 O 3 (YSZ) 8 mol% / LSM at 300 C. 990 nm 540 nm 280 nm -Z''/Ohm 6.00E E E E E C. Brahim, Appl.. Surf. Sci. 253 (2007) 3962 M. Cassir et al. Appl. Surf. Sci., 193 (2002) 120 M. Cassir et al., Patent WO (2002) E E E E E E E E E nm nm nm 3 Z'/Ohm -2 4 ж Sample A Δ Sample B Å Sample C 3-2 Log(σ(S.m-1)) /T(K -1 ) ж Sample A Δ Sample B Å Sample C 300 C E=0.33eV 200 C T( C) E=0.40eV E=0.34eV 100 C activation energies < 1 ev (bulk YSZ) σ i (280)<σ i (540) σ i (990) σ = 1 Rmeas S l

10 Alternative electrolyte, yttria-doped ceria YDC (10/20 mol%) 342 nm, 7 mol% / La 0.8 Sr 0.2 FeO C 400 nm, 6 mol% / ss Z" (Ohms) 1.E+06 8.E+05 6.E+05 4.E+05 2.E+05 YDC layer Electrode reaction 0.05V 0.E+00 0.E+00 2.E+05 4.E+05 6.E+05 8.E+05 1.E+06 1.E+06 1.E+06 Z' (Ohms) 0.1V 0.15V 0.2V 0.25V log (sigma / S.m -1 ) (10000/T) / K YSZ 20at% [7,10] YDC 16at% C 400 C 300 C 200 C - T > 420 C, σydc > σysz - εr 10 x lower / bulk YDC: thin layer better dielectric material E. Ballée et al., Chem. Mater., 2009, 21, nm, 7 mol% / La0.8Sr0.2FeO3

11 ZrO 2 -In 2 O 3 system In mol% 0 0% % 40% 60% 80% 100% -1 log σ (S/cm) Ionic conductivity Electronic conductivity A. Ringuedé, P. Mourot, C. Alvarez Lugano, J-C. Badot and M. Cassir, J. New Mat. for Electrochem. Syst. 9 (2006) Ø Ionic & electronic conductivity = f(in 3+ ratio) In 3+ size close to Zr 4+ r(in 3+ )=0.80 A r(zr 4+ )=0.84 A In 2 O 3 2ZrO 2 2 In ' Zr + 3O Χ Ο + V Ο

12 IDZ ionic conductor 22µm µm 320 nm of IDZ (34 mol%) /LSM 1 µm 480 nm of IDZ (26 mol% ) / LSM 1 µm 380 nm of IDZ (22 mol%) / NiO-YSZ Well-covering, dense and uniform cubic-structured deposits Þ ZrO2 Þ LSM (a) 320 nm IDZ; 34 mol% Þ (b) 480 nm IDZ; 26 mol% Þ (a) Þ Deposition at 300 C Þ Þ (311) (220) (200) (111) Intensité (u.a) λkαco= Å no annealing treatment (b) θ ( ) 70 80

13 ZrO2-In2O3 (gradient) / YSZ IDZ Epaisseur désirée (nm) Composition en InO1,5 désirée (mol%) YSZ 1,06 µm Gradient 1 µm Gradient 1 µm

14 Electrical behaviour of the gradient Log ((R/e)/(Ω/m)) YSZ 30% 50% 65% 90% gradient HT 500 C 400 C % In 65 % R with % In % In = 90 % R 300 C 50% 30% 90% 65% /T /K -1

15 Theoretical/experimental approach of CeO 2 -based catalysts at the SOFC (or MCFC) anode (Ph.D of T. Désaunay, sept. 2012) Ø Oxygen source at SOFC anode: enhancement of hydrogen oxidation / would allow the direct oxidation of CH 4 without carbon deposit Ø State of the surface: fundamental role / reactivity Ø Understanding mechanisms at the molecular level: higher performance Ø Theoretical approach of the behaviour of ceria and its interface reactivity by DFT Ø Nanoparticles of CeO 2 synthesised by hydrothermal route Ø

16 Ø Reactivity: T-programmed reduction (TPR): T order: nanocubes (100) < nanowires (110) < nanooctahedra (111) > > Ea (kj/mol) : 70 < 130 < 430 Ø Thin-layered CeO 2 / NiO-YSZ by ALD Non oriented Y:ZrO 2 (100) Al 2 O 3 (102) SrTiO 3 (100)

17 Thin layers for MCFC by ALD H 2 + CO 2 + H2O Protection of the cathode cathode Anode" Ni + 3% Cr" Li 2 CO 3 -Na 2 CO 3 /LiAlO 2 Ni 2+ Ni (short-circuit) Ni + 3% Cr" Li 2 CO 3 -Na 2 CO 3 /LiAlO 2 Cathode " Li x Ni 1-x O " Thin layer < 1 µm" Ni/NiO O 2 + CO 2! Protection of MCFC separator plates Current collector Anticorrosion layer MCrAlY bond layer Stainless steel Coatings CeO 2 TiO 2 Nb 2 O 5 Co 3 O 4

18 TiO 2 coating (300 nm) / Ni in molten Li 2 CO 3 -K 2 CO 3 at 650 C Before After 230 h Mapping: well-distributed mixed phase Ti-Ni-O TiO 2 + 2Li + +CO 3 2 Li 2 TiO 3 +CO 2 Li x Ti y NiO 3.59 ± 0.06 (x 0.5 and y 0.36): crystal structure similar to NiO Sol. / Ni TiO 2 / Ni TiO 2 / Ni TiO 2 /Ni wt.ppm (50 nm) (150 nm) (300 nm) Ni Ti < 1

19 OCP evolution vs. time in Li 2 CO 3 -K 2 CO 3 at 650 O C, 230 h. a) Ni, b) TiO 2 (50 nm), c) CeO 2 (27 nm), d) Co 3 O 4 (50 nm) Sample Measured Value (wt. ppm) Ni Porous TiO 2 50 nm CeO 2 20 nm Co 3 O 4 50 nm

20 Conclusions Ø Ø Ø Ø ALD deposits Crystalline at low T without annealing Dense, conformal Good composition and thickness control Production of thin layers with composition gradient Speed growth relatively low (15 nm/h IDZ) Pellets µ or nano-structured thin layers Modification of the electrochemical properties with composition gradient Correlation between nanostructures and electrochemical properties? - More active area (surface kinetics enhanced) - Reduced interfacial electrode-electrolyte reactions - Thermal constraints control (rapid ageing of the fuel cell materials) Ø Ø Modelling effort required for complex materials surface organization Use of thin layers in new high-temperature electrochemical devices