Improving the Performance of Ceramic Anode by Exsolved Catalyst Nanoparticles in Solid Oxide Fuel Cells

Transcription

1 Improving the Performance of Ceramic Anode by Exsolved Catalyst Nanoparticles in Solid Oxide Fuel Cells Curtin-UQ Workshop on Nanostructured Electromaterials for Energy Prof. Guntae Kim Ulsan National Institute of Science and Technology (UNIST) School of Energy and Chemical Engineering, S. Korea Contents 1. Introduction 2. SOFC layered perovskite anode 3. Self decorated catalyst by Ex solution 4. Conclusions 1

2 1. Introduction Fuel Cell Choice Fuel cells offer higher efficiency across a wide range of system size. Solid Oxide Fuel Cells (SOFCs) are well suited to large scale applications. 2

3 Type of Fuel Cells 1000 o C Operating temperature o C Type of Fuel cell Solid oxide type (SOFC) Electrolyte Stabilized zirconia (Ceramic) Power Generation Efficiency % 500 o C ~650 o C Molten carbonate type (MCFC) Molten carbonate % ~200 o C Phosphoricacid type (PAFC) Phosphoric acid 35-42% 100 o C Room Temp. to 90 o C Polymer electrolyte type (PEMFC) Ion exchange membrane % Based on the electrolyte materials, each fuel cell has different operating conditions, power generating efficiency. Why develop the fuel cell? Centralized power generation High Cost and Danger Black out Social conflict Risk regulatory cost : $ 43 billion Construction Cost (1GW) : $ 3 billion Radioactive waste cost : $165 billion Ref. Journal of mechine Industrial loss from black out Industry fields Amount of loss Mobile phone $41,000/hour Credit card $2,580,00/hour Financial business $6,480,000/hour Transmission and Distribution loss factor : 4.02 ~ % Substation Substation Pole transformer kv kv kv 220 V Imbalance of Energy supply high voltage, long distance transmission network 3

4 Why develop the fuel cell? Distributed power generation Off the Grid Short period of construction Combined power generation Construction period [unit : year] Distributed power sources LNG Coal Nuclear Green energy Direct Energy supply Transmission network is not required Cheap, Safe, and Eco friendly Application of Fuel Cells AMI, US Sub battery for iphone Bloom Energy, US Portable type Delphi & BMW, US Hyundai Motors, Korea Kyocera, Japan Topsoe, Denmark Simens, US Power generating type Mobile type 4

5 Status of Fuel Cell market in USA GE Threatens to Enter Fuel Cell Market, Compete With Bloom General Electric(GE) announced that it is initiating an entrepreneurial effort to commercialize its solid oxide fuel cell (SOFC) technology for megawattscale stationary power applications. GE has claimed a recent fuel cell "breakthrough" with an efficiency of 65 percent and an overall efficiency of up to 95 percent when waste heat is captured. GE plans to build a pilot plant and development facility near Saratoga Springs, New York. GE will test a 50 kilowatt system at Hudson Valley Community College s TEC-SMART facility next door. The GE Conglomerate had $146 billion in revenue last year. Status of Fuel Cell market in USA & Japan Softbank-bloom energy Japan :$10M In Fukuoka, Softbank building, 200kw unit Efficiency: 52%, fuel: city gas 5

6 Status of Fuel Cell market in Japan ENE-FARM Operation tem.: o C, efficiency: 46.5% Status of Fuel Cell market in Japan Price : 3 million dollars (including setting cost) 1.5 million dollars (only SOFC + turbine system, excluding setting cost) Cell stack cartridge 6

7 Status of Fuel Cell market in Korea LG buys controlling stake in Rolls-Royce fuel cell business. Status of Fuel Cell market in Korea Technology : Solid Oxide Fuel Cell Basic concepts (type of cell, stack configuration, core components) Status of performance, key characterizations 5kW SOFC Engine Hybrid System 7

8 Basic principle of Solid Oxide Fuel Cells (SOFCs) Electrochemical Reactor which converts chemical energy directly into electrical energy Advantages Direct conversion of fuel into electricity High efficiency Environmentally friendly Fuel flexibility (any hydrocarbon) Conventional SOFCs use H 2 or mixtures of H 2 and CO Cathode: Oxygen from the air is reduced O 2 + 4e 2O 2 Anode: Oxidation of fuel H 2 + O 2 H 2 O + 2e Fuels : H 2, CH 4, C 3 H 8, JP8, diesel etc. Internal steam reforming of CH 4 External reforming of higher hydrocarbons Oxy reforming reduces efficiency by ~30% 2. SOFC layered perovksite anode :PrBaMn 2 O 5+d 8

9 Disadvantage of H 2 fuel 1. Expensive & dependence on fossil fuels 2. Storage While widely available, hydrogen is expensive. Other non renewable sources such as coal, oil and natural gas are needed to separate it from Super light hydrogen is hard to transport in Need to oxygen. a reasonable fashion. using direct 3. Not easy to replace existing infrastructure hydrocarbon 4. Highly Flammable for SOFC There is no existing infrastructure in place to accommodate hydrogen as a fuel source for the average motorist. Hydrogen in itself is a very powerful source of fuel. It s highly inflammable. What issue? Conventional Anode Material Conventional anode material : Ni YSZ cermet High electronic conductivity Excellent activity for clean reformed fuels Chemically and physically compatible with YSZ electrolyte Traditional SOFC use Ni based anodes: 1. Low carbon coking tolerance 2. Sensitive to sulfur in the fuel (X) 3. Anodes cannot tolerate re oxidation (Ni NiO Ni) Developing new anode materials instead of Ni based anode 9

10 Requirements of Anode Material Materials Compatibility Thermal expansion Solid State Reaction Electrical Conductivity High electrical conductivity in reducing condition + Good Tolerance Carbon coking Sulfur poisoning Catalytic Activity Operation at lower temperature Enhance active site density For Direct Hydrocarbon Fuels Good SOFC Anode Material Properties of layered PrBaMn 2 O 5+d (PBMO) Oxygen Deficient Layered Perovskite as Efficient and Stable Anode : PBMO S. Sengodan, G. Kim*, Nature Materials (2015) 14,

11 Layered perovskite structure Simple perovskite oxide (ABO 3 d ) Double perovskite oxide (AA B 2 O 5+d ) A : La, Sr, Ca, and Ba, etc. Coordinated to twelve oxygen atoms B : Ti, Cr, Ni, Fe, Co, and Mn, etc. Coordinated to six oxygen atoms. A B O A A' B O O A : La, Pr, Nd, Sm, Gd A : Ba, Sr B : Co, Fe, Mn, Cu Double structure Significant size difference between the large Ba and the smaller Ln. Cation ordered perovskite structure? Recently, new cathode materials have gotten an attention. Ordered perovskite structure, PrBaCo 2 O 5+ Comparison of diffusion coefficient Comparison of surface exchange coefficient Ordered perovskite is faster oxygen kinetics than disorder perovskite G. Kim, J. Mater. Chem., v.17, p (2007) 11

12 Layered perovskite structure (AA B 2 O 5+ ) Lattice Oxygen Ba Mobile oxygen Ln Co Simple perovskite (ABO 3 Layered perovskite (AA B 2 O 5+ Size difference between the large Ba cation and the smaller Ln cation Layered perovskite structure 2. SOFC Layered perovskite papers since 2006 Layered perovskite papers Search the number of publication for DP: ~ 400 Including the application of SOFC, SOE, H + SOFC O. Kwon, G. Kim*, Angewandte chemie Int. Ed on press (2015) S. Sengodan, G. Kim *, Nature Materials 14, 205 (2015) S. Yoo, G. Kim *, Angewandte chemie Int. Ed. 53, (2014) Cover page S. Choi, G. Kim *, Scientific Reports 3, 2426 (2013) La: G.Kim, Solid State Ionics, 177, 1461 (2006), G. Kim, Electrochem. Solid State Lett., 11, B16 (2008), G. Kim, Chem. Mater., 22, 776 (2010), S. Choi, G. Kim Electrochem. Commun., 32, 5 (2013) Pr: G.Kim, Appl. Phys. Lett., 88, (2006), G. Kim, Appl. Phys. Lett., 90, (2007), G. Kim, J. Mater. Chem., 17, 2500 (2007), S. Park, G. Kim, ECS Electrochemistry Letters, 1 (5), F29 (2012), S. Choi, G. Kim J. Power Sources 2011, 10 (2012), S. Park, G. Kim RSC Advances, 4, 1775 (2014) S. Park, G. Kim Electrochim. Acta, 125, 683 (2014), S. Choi, G. Kim J. Mater. Chem. A, 3, 6088 (2015) Nd: S. Yoo, G. Kim J. Mater. Chem., 21, 439 (2011), S. Yoo, G. Kim J. Electrochem. Soc., 158 (6) B632 (2011), S. Yoo, G. Kim Electrochimica Acta, 100, 44 (2013), J. Kim, G. Kim J. Mater. Chem. A, 1, 515 (2013), J. Kim, G. Kim Electrochim. Acta, 112, 712 (2013), C. Kim, G. Kim Int. J. Hydrogen Energy, 39, (2014), J. Kim, G. Kim ChemSusChem, 7, 1669 (2014) Sm: A. Jun, G. Kim Int. J. Hydrogen Energy, 27, (2012), A. Jun, G. Kim Phys.Chem.Chem.Phys., 15, (2013), Y W. Ju, G. Kim, J. Electrochem. Soc., 161 (5) F668 (2014), A. Jun, G. Kim Int. J. Hydrogen Energy, 39, (2014) Gd: J. Kim, G. Kim J. Am. Ceram. Soc., 97, 651 (2014) 12

13 Fabrication of fuel cell LSGM based electrolyte supported cell LSGM :La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 δ PBMO anode Anode : PrBaMn 2 O 5+ (PBMO) LDC buffer layer Cathode : NdBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+ (NBSCF) LSGM electrolyte Fuel cell test conditions Structural Property A site ordering synthesis concept Principle of the approach to prepare A site layered perovskite PBMO Air synthesis PBMO Air synthesis PBMO Layered PBMO Phase changes from Simple to Layered Perovskite Layered PBMO Exothermic peak (*) Phase change occurs upon heating at 400 o C in reducing condition. 13

14 Structure Property TEM analysis Surface area 2.42 m 2 /g Surface area 5.32 m 2 /g S. Sengodan, G. Kim *, Nature Materials 14, 205 (2015) 2. SOFC Electrode Anode (PrBaMn 2 O 5+ ) S. Sengodan, G. Kim *, Nature Materials 14, 205 (2015) Cell performance is almost constant without degradation for 500 hours in C 3 H 8 PBMO anode High electrical conductivity in H 2 Excellent redox property Good carbon coking tolerance Highly efficient and stable anode material 14

15 3. Self decorated catalyst by Ex solution 3. Ex solution Ex solution Metal nanoparticles ex solution from the perovskite oxide host in a reducing environment. The ex solved metal nanoparticles with small size may act as high active sites for oxidation reaction of hydrocarbon during the cell operation DAIHATSU TOYOTA COLLABORATIVE RESEARCH Y. Nishihata, et al. Nature. 2002, 418, 164. D. Neagu, et al. Nat. Chem. 2013, 5, D. Neagu, et al. Nat. Commun. 2015, 6,

16 3. Ex solution layered perovskite_pbm?? PBMO or PBMCO (anode) LDC (buffer layer) LSGM (electrolyte) NBSCF50-GDC (cathode) Thickness of LSGM : 250 m Qualitative analysis : XRD, SEM, TEM Quantitative analysis : DFT Electrochemical performance : Impedance, Power density PLD : PBMO and PBMCO samples deposit on the Al 2 O 3 film. 3. Ex solution SEM of bulk electrode, Mn vs. Co Pr 0.5 Ba 0.5 MnO 3 Pr 0.5 Ba 0.5 Mn 0.85 Co 0.15 O 3 After Reduction in H 2 PrBaMn 2 O 5+ PrBaMn 1.7 Co 0.3 O 5+ Co PrBaMn 1.7 Co 0.3 O 5+ MnO PrBaMn 2 O 5+ (a,b) the surface of the before reduced samples is smooth without any nanoparticles on the surface. (c,d) some small nanoparticles of 20~50 nm diameter are observed on the surface of reduced samples 16

17 3. PLD thin film_ex solution TEM MnO PBMO Co PBMCO PBMO and PBMCO films on Al 2 O 3 were reduced at 800 o Cfor 10 min The lattice constants of the MnO and Co correspond to each XRD data In situ growth of nanoparticles through control of non stoichiometry PBMO PBMCO D. Neagu, et al. Nat. Chem. 2013, 5,

18 3. Ex solution DFT Calculation 0.47 ev 0.55 ev Mn Co 2.97 ev 2.46 ev O Ba Pr PBMO PBMCO PBMO PBMCO Segregation energy Oxygen vacancy formation energy (a) Schematic of B metal segregation (b) Schematic of oxygen vacancy formation on the surfaces The co segregation energies are 0.47 and 0.55eV for PBMO and PBMCO, respectively Co is more favorable to segregate towards the surface than Mn The oxygen vacancy formation energies are 2.97 ev and 2.46 ev for PBMO and PBMCO, respectively, in the surface. Collaboration with Prof. J. Hahn, University of Seoul 3. Ex solution DFT Calculation Mn Co O Ba Pr PBMO PBMCO 1layer layer layer layer PBMO PBMCO Side views of (a) PBMO and (b) PBMCO on the surface, respectively. The most stable sites of oxygen vacancy formation in PBMO and PBMCO are both near the surfaces. Thus, oxygen vacancy formed in the bulk prefers to be segregated out to the surfaces. The oxygen vacancy are more preferentially formed in PBMCO than in PBMO at each layer. the principle of exsolution 18

19 3. Ex solution electrochemical properties Fabrication Technique : screen print on LSGM supported Anode : Ceramic anode Cathode : NdBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+ GDC composite 0.66 W cm 800 o C in H W cm 800 o C in H 2 Ceramic anode Electrolyte Thickness (μm) Temperature ( o C) Maximum Power density (W cm -2 ) Layered PBMO Layered PBMCO No external Catalysts!! Conclusion Anode material A PrBaMn 2 O 5+ demonstrates superior SOFC ceramic anode performance and stability in various fuels. Layered anodes exhibit high electrical conductivity, excellent redox and coking tolerance. On the basis of the number of good properties, layered PBMO is an attractive anode material for SOFC applications. Ex solution The unique or exclusive structural phase transition in perovskite ceramic anode potentially offers a new approach to produce nanoparticle decorated perovskite surface for next generation electrodes for SOFCs. No need external catalysts 19

20 Many thanks to Prof. Jeeyoung Shin (Dong Eui Univ.) Dr. Seonyoung Yoo Dr. Sivaprakash Sengodan Dr. Sihyuk Choi Areum Jun Seonhye Park Junyoung Kim Oh hun Gwon Seona Kim Changmin Kim Oh hoon Kwon Chaehyun Lim Dongwhi Jung Sangwook Joo Chanseok Kim Prof. Young wan Ju Thank you for your attention 20