Fuel Cell Technology Status, Challenges, and Opportunities

Transcription

1 Fuel Cell Technology Status, Challenges, and pportunities eilin Liu School of aterials Science &Engineering Georgia Institute of Technology Atlanta, GA Presented to Electrical Energy Systems and Sustainability Workshop Georgia Tech ovember 29 December 1, 2000

2 utline Introduction Polymer Electrolyte embrane Fuel Cells Current technology Applications: Portable/vehicle Challenges/opportunities Solid xide Fuel Cells (SFCs) Current technology Applications:Stationary/distributed/EV Challenges/opportunities Concluding Remarks

3 Schematic of an individual fuel cell e Load Fuel in xidant in H 2 2 H 2 H + H 2 H 2 Anion conductor 2 Depleted fuel Anode Electrolyte (Ionic conductor) Cathode Depleted oxidant

4 Advantages of Fuel Cells ver conventional Technologies High efficiency Internal combustion engine: <30% Fuel cell: 50% electrical, 85% overall (SFC) Environmental friendly Emits H 2 or C 2 without pollutants Emits as much as 60% less C 2 than coal plant oise-free and no site restriction o mechanical friction or moving parts

5 PEFCs: Challenges & pportunities Efficient catalysts insensitive to impurities in the fuel such as C; Efficient catalysts that promote a high rate of oxygen reduction; Alternative catalysts less expensive than Pt to reduce the cost.

6 A Planar Solid xide Fuel Cell End Plate Anode Electrolyte Cathode Bipolar Separator Repeating unit Anode

7 A Tubular Solid xide Fuel Cell

8 Characteristics of GDC Powder by GP Large surface area Compositional homogeneity b 4µm 1µm Loose agglomerates Foam-like structure Fill density g/cm th of theoretical value Easy to densify 92% at 1250 o C/5 hrs 95% at 1350 o C/5 hrs

9 icrostructures of Dry-Pressed Films 10µm 30µm GDC film cathode electrolyte Substrate anode ~8 µm ~15 µm

10 SFCs Fabricated by Screen-Printing A single cell cathode Porous SSC and 10 v%sdc Cathode electrolyte anode 30µm 2µm Dense SDC Porous i-sdc Anode 2µm 2µm Changrong Xia, Fanglin Chen and eilin Liu, Electrochemical and Solid State letters, 4(5) A52-A54 (2001).

11 Single cell performance of SDC-electrolyte SFC o C 550 o C 500 o C 450 o C 400 o C 0.5 Cell Voltage, V Power density, Wcm Current Density, A/cm 2

12 Significance of Interfacial Resistances Resistance, Ωcm 2 Im Z, Ωcm a 600 o C 550 o C Resistance, Ωcm Re Z, Ωcm o C Ea=115kJmol -1 Ea=32kJmol -1 Electrolyte Electrodes /T, k -1 Electrolyte resistance Electrodes polarization Total resistance Temperature, o C

13 SFCs: Challenges & pportunities ew electrolytes with high ionic conductivities at low temperatures inexpensive materials,longer life; onstructural electrodes and interfaces to enhance performance, especially anodes for alternative fuels; Cost-effective fabrication processes to dramatically reduce the cost; $4,000 $400/KW; Efficient catalysts insensitive to impurities in the fuel such as H 2 S.

14 esoporous aterials eso-porous materials---porous inorganic solids with pore size 2-50nm Preparation -- surfactant templating mechanism Surfactant Inorganic precursor Remarkable properties: arrow pore size distribution Pore size tunable (from 2nm to 50 nm) Large surface area (~1000 m 2 /g) Applications: Catalysis, selective separations, absorption medium, sensors, Electrodes for lithium batteries, fuel cells, and gas sensors.

15 Formation of esoporous 2 2- [(H) 6 ] Cl 4 Tin chloride ph=10 2- [(H) 6 ] H 3 C + Br - CH 3 Cetyltrimethylammonium bromide + 2- CH 3 [(H) 6 ] + Electrostatic interaction 2- [(H) 6 ] + [(H) 6 ] C [(H) 6 ] [(H) 6 ] 2-2- [(H) 6 ] Aging icelle formation S + I - interaction Calcining 10 nm TE image of 2

16 Preparation of esoporous YSZ-i -PP (Surfactant) (PE) m (PP) n (PE) m ZrCl 2 YCl 3 + icl 2 + (Inorganic species) YCl 3 RH H R Y Cl Cl Cl H YCl 2 H R + H 2 -PE R YCl 2 + HCl

17 TG-DSC, XRD of esoporous YSZ-i TG o C/2hr x x o YSZ x i 500 o C/2 hr Weight change (%) DSC Heat flow (mw) Intensity As-synthesized o o o x o o x o As-synthesized Temperature ( o C) θ (degree)

18 TE and BET of esoporous YSZ-i 20 nm Vol adsorbed (cc/g, STP) m 2 /g 4.5 nm Relative pressure (P/Po) TE BET

19 icrographs of PS & Sr 0.5 Sm 0.5 Co nm 500 nm Polystyrene Spheres Sr 0.5 Sm 0.5 Co 3

20 Concluding Remarks Fuel Cells are the most efficient/cleanest technology for conversion of chemical to electrical energy; PEFC and SFC are the most versatile system for various applications; Cost reduction is the key to successful commercialization of fuel cells; Fuel cells will significantly influence our everyday life in the years to come.