Georgia Tech - SSI&EC Meilin Liu School of Materials Science &Engineering Georgia Institute of Technology Atlanta, GA Presented to Electrical Energy Systems and Sustainability Workshop Georgia Tech November 29 – December 1, 2000 Fuel Cell Technology Status, Challenges, and Opportunities

Georgia Tech - SSI&EC Outline Introduction Polymer Electrolyte Membrane Fuel Cells –Current technology –Applications: Portable/vehicle –Challenges/opportunities Solid Oxide Fuel Cells (SOFCs) –Current technology –Applications:Stationary/distributed/EV –Challenges/opportunities Concluding Remarks

Georgia Tech - SSI&EC Fuel in Oxidant in Depleted fuel Depleted oxidant Electrolyte (Ionic conductor) CathodeAnode H+H+ Anion conductor H2H2 O2O2 H2OH2O H2OH2O Load e’ O2O2 H2H2 Schematic of an individual fuel cell

Georgia Tech - SSI&EC Advantages of Fuel Cells Over conventional Technologies  High efficiency Internal combustion engine: <30% Fuel cell: 50% electrical, 85% overall (SOFC)  Environmental friendly Emits H 2 O or CO 2 without pollutants Emits as much as 60% less CO 2 than coal plant  Noise -free and no site restriction No mechanical friction or moving parts

Georgia Tech - SSI&EC PEMFCs: Challenges & Opportunities Efficient catalysts insensitive to impurities in the fuel such as CO; Efficient catalysts that promote a high rate of oxygen reduction; Alternative catalysts less expensive than Pt to reduce the cost.

Georgia Tech - SSI&EC A Planar Solid Oxide Fuel Cell End Plate Anode Electrolyte Cathode Bipolar Separator Anode Repeating unit

Georgia Tech - SSI&EC A Tubular Solid Oxide Fuel Cell

Georgia Tech - SSI&EC Characteristics of GDC Powder by GNP 1m1m b 4m4m Easy to densify 92% at 1250 o C/5 hrs 95% at 1350 o C/5 hrs Large surface area Compositional homogeneity Loose agglomerates Foam-like structure Fill density g/cm th of theoretical value

Georgia Tech - SSI&EC Microstructures of Dry-Pressed Films 30  m cathode electrolyte anode ~15  m GDC film Substrate ~8  m 10  m

Georgia Tech - SSI&EC 2m2m Dense SDC 2m2m Porous SSC and 10 v%SDC Cathode Changrong Xia, Fanglin Chen and Meilin Liu, Electrochemical and Solid State letters, 4(5) A52-A54 (2001). SOFCs Fabricated by Screen-Printing Porous Ni-SDC Anode 2m2m electrolyte anode cathode A single cell 30  m

Georgia Tech - SSI&EC Single cell performance of SDC-electrolyte SOFC

Georgia Tech - SSI&EC Significance of Interfacial Resistances

Georgia Tech - SSI&EC SOFCs: Challenges & Opportunities Nonstructural 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. New electrolytes with high ionic conductivities at low temperatures  inexpensive materials,longer life;

Georgia Tech - SSI&EC Mesoporous Materials Meso-porous materials---porous inorganic solids with pore size 2-50nm Preparation -- surfactant templating mechanism Remarkable properties: Narrow pore size distribution Pore size tunable (from 2nm to 50 nm) Large surface area (~1000 m 2 /g) Surfactant Inorganic precursor Applications: Catalysis, selective separations, absorption medium, sensors, Electrodes for lithium batteries, fuel cells, and gas sensors.

Georgia Tech - SSI&EC Formation of Mesoporous SnO 2 Cetyltrimethylammonium bromide Electrostatic interaction Tin chloride Micelle formation S + I - interaction Aging Calcining TEM image of SnO 2

Georgia Tech - SSI&EC Preparation of Mesoporous YSZ-NiO -PPO (Surfactant) (PEO) m (PPO) n (PEO) m ZrOCl 2 YCl 3 + NiCl 2 + (Inorganic species) Y Cl 3 ROH O H R Y HO YCl 2 HO R+ HO 2 -PEO RO YCl 2 + HCl

Georgia Tech - SSI&EC TG-DSC, XRD of Mesoporous YSZ-NiO o o o oo o x x x x o—YSZ x—NiO

Georgia Tech - SSI&EC TEM and BET of Mesoporous YSZ-NiO TEM BET 108 m 2 /g 4.5 nm

Georgia Tech - SSI&EC Micrographs of PS & Sr 0.5 Sm 0.5 CoO nm Polystyrene Spheres 500 nm Sr 0.5 Sm 0.5 CoO 3

Georgia Tech - SSI&EC Concluding Remarks  Fuel Cells are the most efficient/cleanest technology for conversion of chemical to electrical energy;  PEMFC and SOFC 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.