Anodes for Direct Hydrocarbon Solid Anodes for Direct Hydrocarbon Solid Oxide Fuel Cells (SOFC’ ’s) s) Oxide Fuel Cells (SOFC Challenges in – – materials selection and materials selection and Challenges in deposition deposition Venkatesan Venkatesan V. Krishnan V. Krishnan Department of Chemical Engineering Department of Chemical Engineering IIT Delhi IIT Delhi
Barriers to the hydrogen economy Barriers to the hydrogen economy • How to make hydrogen (SR, electrolysis, Solar, Borohydride)? • Loss of efficiency in making hydrogen • Storage and Transportation? • SOFC’s can work with any ‘fuel’ • Let us work in parallel with the Hydrogen advocates by using hydrocarbons directly with SOFC’s • Do not forget – well to wheels efficiency!
DIRECT OXIDATION OF DIRECT OXIDATION OF HYDROCARBONS AND OXYGENATES HYDROCARBONS AND OXYGENATES Reactions: Cathode: (x + y/4 - z/2) O 2 + (4x + y- 2z) e (2x + y/2 - z) O 2- Anode: C x H y O z + (2x + y/2 - z) O 2- (y/2) H 2 O + x CO 2 + (4x + y - 2z) e Overall: C x H y O z + (x + y/4 - z/2) O 2 (y/2) H 2 O + x CO 2 Natural Gas, Propane/ Butane (LPG), Naphtha, Diesel, Alcohols, Natural Gas, Propane/ Butane (LPG), Naphtha, Diesel, Alcohols, Syngas (from coal and biomass) Syngas (from coal and biomass) WHAT HAPPENS IN THE ANODE IN SUCH CASES ? WHAT HAPPENS IN THE ANODE IN SUCH CASES ? - � � CO - Direct oxidation; Direct oxidation; CH - 2- CH 4 + 4O 2 CO 2 + 2H 2 O + 4e 4 + 4O 2 + 2H 2 O + 4e � CO + 3H - Internal reforming; Internal reforming; CH O � - CH 4 + H 2 CO + 3H 2 4 + H 2 O 2 - � � CO - Syngas oxidation; Syngas oxidation; CO + H - + O 2 2- CO + H 2 CO 2 + H 2 O 2 + O 2 + H 2 O 4 � � CH - Coke deposition (thermal, catalytic); Coke deposition (thermal, catalytic); CH - CH 4 CH x + H 2 x + H 2
WHY DO WE NEED NEW ANODES WHY DO WE NEED NEW ANODES • Incompatibility of Ni Incompatibility of Ni- -YSZ anodes with any fuel other YSZ anodes with any fuel other • than H 2 – reforming essential; reforming essential; coking with dry coking with dry than H 2 – hydrocarbons � � Reference: Toebes et al. Reference: Toebes et al. hydrocarbons • Poisoning of Ni Poisoning of Ni- -YSZ by YSZ by sulfur compounds sulfur compounds • • Poor Redox tolerance Poor Redox tolerance of Ni of Ni- -based anodes based anodes • • YET, must satisfy the basic needs of SOFC anodes YET, must satisfy the basic needs of SOFC anodes – – • – Electronic conductivity Electronic conductivity – – Ionic conductivity Ionic conductivity – – Good catalytic activity Good catalytic activity – – Compatibility of Compatibility of CTE CTE’ ’s s with that of electrolyte with that of electrolyte –
EFFECT OF COKING ON Ni- -YSZ ANODES YSZ ANODES EFFECT OF COKING ON Ni 20% CO/7% H 2 550°C. Ni particles Toebes et al. (2002) Toebes et al. (2002) In H 2 , 800 o C, 3 hrs In CH 4 , 800 o C, 3 hrs Coking due to decomposition and/or Bouduard Reaction
ALTERNATIVE ANODES ? ALTERNATIVE ANODES ? Cu/CeO 2 /YSZ Gorte et al. (2000) Cu/CeO 2 /YSZ Perovskites, Irvine et al. Perovskites, Irvine et al. Gorte et al. (2000) Boukamp, et al. , et al. Boukamp Lanthanides/ Alkali earth Metal ions Ce 0.9 Gd 0.1 O 1.95 combined with Ce 0.9 Gd 0.1 O 1.95 combined with Oxygen ions Transition metal ions (La 0.8 Sr 0.2 ) (Cr 0.8 Mn 0.2 )O 3 (La 0.8 Sr 0.2 ) (Cr 0.8 Mn 0.2 )O δ - δ 3- Barnett et al. (2002) AB BO O 3 Barnett et al. (2002) A 3 Irvine et al. (2001) Irvine et al. (2001) Titania- -Niobia, Nb Niobia, Nb 2 TiO 7 Titania 2 TiO 7- -x x Irvine et. al. (2003) – – Irvine et. al. (2003) (La 0.8 Sr 0.2 ) (Cr 0.5 Mn 0.5 )O 3 (La 0.8 Sr 0.2 ) (Cr 0.5 Mn 0.5 )O δ - δ 3-
Why perovskites??? Why perovskites??? • • Ionic and electronic conductivity can be tailored Ionic and electronic conductivity can be tailored • Good Hydrocarbon oxidation catalytic activity has been • Good Hydrocarbon oxidation catalytic activity has been reported. reported. • No coking • No coking • Good thermal and redox stability • Good thermal and redox stability • And yet, concern remains – – do we have adequate do we have adequate • And yet, concern remains electronic conductivity under reducing conditions? electronic conductivity under reducing conditions?
Review of work on alternate anodes - - Gorte et al. Gorte et al. Review of work on alternate anodes • Anodes based on Copper – conductor; Ceria – electrocatalyst – Cu and CeO 2 deposited on pre-formed porous anode substrates – Intermediate temperature SOFC’s • Considerable data on butane, methane, diesel, propane – – Anode stable over long periods of time – Direct electrochemical Oxidation observed in button cells – Workable with fuel with existing sulfur levels • Technology transfer to Franklin Fuel Cells, PA, US – Demonstration level, with diesel, gasoline and ethanol • Performance tends to be lowered due to Copper sintering; enhancement necessary by carbon deposition • Little/ no data on redox tolerance (deposition technique may be advantageous, use of Vol % < 20%)
Gorte et al., cont’ ’d d Gorte et al., cont 1.5 1.5 0.20 0.20 C C 1.2 1.2 0.16 0.16 0.9 0.9 0.12 0.12 P P V V C C 0.6 0.6 0.08 0.08 0.3 0.3 0.04 0.04 A A B B 0.0 0.0 0.00 0.00 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 I, A/cm 2 I, A/cm 2 1E +05 Effective Conductivity, S/cm 1E +03 Overall 1E +01 ‘connectivity’ of Cu Compare with Ni-YSZ is good, leading to made by solid state 1E -01 about 4300 S/cm methods (from 4-point probe) 1E -03 0 5 10 15 20 25 30 Volume Percent Cu, %
Performance, Conductivity with Cu content Performance, Conductivity with Cu content • Carbon enhancement 5000 0.25 occurs even at 25% Vol , Conductivity, S/cm Cu; constant, independent Max. P D, W/cm 2 4000 (w) carbon 0.20 of Cu 3000 0.15 • But sufficient Performance conductivity is attained 2000 0.10 with less than 10% (w/o) carbon Conductivity 1000 0.05 volume Overall conductivity not the 0 0.00 σ σ problem; the issue is proper 0.00 0.05 0.10 0.15 0.20 0.25 0.30 ‘connectivity’ at the 3- Volume fraction of Cu phase boundary
), LSCM δ ), Irvine et al. (2003) (La Irvine et al. (2003) (La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3 LSCM 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O - δ 3- Conductivity of perovskite at 850 o C Max. P. D. (W/cm 2 ) = 0.47, 900 o C - in air, 28 S/cm Max. P. D. in Methane = 0.3 W/cm 2 - in reducing atmosphere, 1.12 S/cm (at 950 o C)
Irvine et al., Niobia- -Titania rutile system (2001) Titania rutile system (2001) Irvine et al., Niobia • Max. conductivity under reduction, 300 S/cm • Max. conductivity under reduction, 300 S/cm • Good catalytic activity towards methane • Good catalytic activity towards methane Oxidation Oxidation Reduction
Barnett et al. (2002) – – LSCM LSCM- -GDC composite GDC composite Barnett et al. (2002) Ce 0.9 Gd 0.1 O 1.95 – ionic conduction ionic conduction Ce 0.9 Gd 0.1 O 1.95 – Small qty of Ni + Small qty of Ni + − electronic conduction δ − (La 0.8 Sr 0.2 ) (Cr 0.8 Mn 0.2 )O 3 electronic conduction (La 0.8 Sr 0.2 ) (Cr 0.8 Mn 0.2 )O - δ 3- • Usage of LSCM – high electronic conductivity in reducing conditions, as well • Compatible with GDC electrolytes Compared to Ni- -GDC, performance in C GDC, performance in C 3 H 8 is significantly higher Compared to Ni 3 H 8 is significantly higher
Focus of research at Chemical Eng. Dept., IIT- -D D Focus of research at Chemical Eng. Dept., IIT • Nature of work essentially fundamental - - ‘ ‘button cells button cells’ ’ • Nature of work essentially fundamental • Aim is to contribute to existing knowledge ‘ ‘pool pool’ ’, via publications , via publications • Aim is to contribute to existing knowledge and patents by addressing problems involving Electrochemistry, and patents by addressing problems involving Electrochemistry, Materials and Catalysis Materials and Catalysis • We look forward to collaborate with ‘ ‘developmental laboratories developmental laboratories’ ’, , • We look forward to collaborate with e.g., test our ideas on a larger scale – – CGCRI, BHEL R&D CGCRI, BHEL R&D e.g., test our ideas on a larger scale What we are involved in - - What we are involved in • SOFC component fabrication – – tape casting, sintering, painting, tape casting, sintering, painting, • SOFC component fabrication impregnation impregnation • Characterization of components – – bi bi- -layers, catalysts layers, catalysts – – SEM, SA/ SEM, SA/ • Characterization of components PSD, Porosity, XRD, Thermal Analysis PSD, Porosity, XRD, Thermal Analysis • Testing of Electrical Conductivity • Testing of Electrical Conductivity • Fuel Cell Testing • Fuel Cell Testing
FUEL CELL REACTOR AND OPERATION FUEL CELL REACTOR AND OPERATION Cathode Lead (Ag/ Pt) Ceramabond, adhesive LSM-YSZ Cathode 1/2” OD Alumina tube Fuel Air Ag/ Pt mesh Anode Lead, Au Anode
Tape Casting (non- -Aq Aq) ) Tape Casting (non Component Component Component Component Quantity Quantity function function Powder Powder YSZ YSZ 15g 15g Solvent Solvent M EK M EK 20mL 20mL EtO H EtO H 10mL 10mL Dispersant Dispersant Oleic A cid Oleic A cid 0.5mL 0.5mL Binder Binder PVB PVB 2.0g 2.0g Plasticizer Plasticizer PEG PEG 1.2mL 1.2mL
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