SOLID OXIDE FUEL CELL BASED ON PROTON- CONDUCTING CERAMIC ELECTROLYTE* U. (Balu) Balachandran, T. H. Lee, and S. E. Dorris Argonne National Laboratory Energy Systems Division *Work supported by the U.S. Dept. of Energy, Presented at the NHA Annual Hydrogen Conference, Long Beach, CA, May 3-6, 2010

NHA Hydrogen Conference, Long Beach, CA, May 3-6, cathode Fuel (H 2 ) H+H+ External Load e-e- e-e- proton conductor (electrolyte) anode Oxidant (air) H2OH2O Overall reaction: H 2 +1/2O 2 H 2 O SOFC based on Proton Conducting Oxides Advantages:  Lower (intermediate) temperature of operation –Overcomes material issues such as seals, inter- diffusion, interconnects, etc.  No dilution of the fuel (water is not formed in the fuel side)  Prevent anode coking by internal self-regulated methane reforming

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Why BaCe 0.8 Y 0.2 O 3 (BCY20) Electrolyte? J. Guan, S. E. Dorris, U. Balachandran, and M. Liu, Solid State Ionics 100 (1997) 45 4% H 2 BaCe(Y)O 3 : highest total proton conductivity among perovskite type oxides. 20 % Y doped barium cerate showed the highest total conductivity. BCY20 has been developed as a potential hydrogen separation membrane material. Ni/BCY is stable in gas streams containing H 2 O, CO & CO 2 at °C (≈200 hr test)

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Potential application of hydrogen pump —Hydrogen separator —Steam electrolyzer —Membrane reactor —Hydrogen gas compressor cathode H2H2 H+H+ H2H2 galvanostat (D.C. source) e-e- e-e- proton conductor anode Electrochemical Hydrogen Pumping

NHA Hydrogen Conference, Long Beach, CA, May 3-6, H 2 Evolution Rate vs. Input Current Density (cathode surface area 0.5 cm 2 )

NHA Hydrogen Conference, Long Beach, CA, May 3-6, BaCe 0.8 Y 0.2 O 3-  (BCY) Film Preparation Colloidal Spray Deposition (CSD)* BCY Colloid BCY powder (Praxair) was dispersed in isopropyl alcohol. Substrate (NiO/BCY composite) Green substrate (1” O.D.) was partially for 12 h. Film Green film was prepared by a colloidal spray deposition. Disk sintering Disks were for 5 h. *A. Pham, T. H. Lee, and R. S. Glass, Proc. 6th Int. Symp. on Solid Oxide Fuel Cells, Electrochem. Soc., PV (1999) 172. *A. Pham, R. S. Glass, and T. H. Lee, U.S. Patent No (2002).

NHA Hydrogen Conference, Long Beach, CA, May 3-6, SEM Micrographs of BCY Film (as-sintered surface) Dense BCY film with an average grain size of ≈4  m.

NHA Hydrogen Conference, Long Beach, CA, May 3-6, NiO/BCY SEM Micrographs of Fracture Surface (Film & Substrate)  Uniform film thickness.  Film is well-bonded to the substrate.

NHA Hydrogen Conference, Long Beach, CA, May 3-6, (80% H 2 / balance He) Schematic of Experimental Setup

NHA Hydrogen Conference, Long Beach, CA, May 3-6, I-V and Power Density of a Cell (≈10-  m thick BCY electrolyte; H 2 /wet air)

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Temp. ( o C) OCV(Volt, measured) OCV (Volt, theoretical) where, E o is the EMF at standard pressure. Open-circuit voltage of a BCY20-based fuel cell (H 2 /wet air)

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Power Outputs of Laboratory Fuel Cells using Proton-Conductors Ref: K. D. Kreuer, Annu. Rev. Mater. Res., 33, 333, Compilation of laboratory fuel cells operating with proton-conducting oxides as electrolytes and their reported maximum power outputs 1.4 W/cm 600°C with 0.7 micron thick BCY electrolyte (N. Ito et al., J. Power Sources, 152, 200, mW/cm 2 at 800°C (present work - 10 micron thick electrolyte)

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Cell Voltage Vs. Current Density (≈10-  m thick BCY electrolyte; 800°C) Voltage drop across the electrolyte (IR drop) was calculated using the resistance of the electrolyte measured at open- circuit condition by impedance analyzer. Curvature of the I-V data indicates concentration polarization (diffusion overpotential) at high current density. The voltage drop at 800°C is mainly due to electrode polarization 800°C

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Cell Voltage Vs. Current Density (≈10-  m thick BCY electrolyte; 500°C) At 500°C, polarization loss is still dominant, but the contribution of IR loss increases (because of decrease of ionic conductivity). At low current densities, the drop is from the activation polarization as indicated by the curvature of the data. Concentration polarization dominates at high current densities.

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Conductivities of Proton- & Oxide-ion Conductors Ref: K. D. Kreuer, Annu. Rev. Mater. Res., 33, 333, Bulk (grain) proton conductivity of Y:BaZrO 3 compared with the oxide ion conductivity of the best oxide ion ceramics

NHA Hydrogen Conference, Long Beach, CA, May 3-6, Summary  Successfully prepared dense and crack-free thin films of BCY on NiO/BCY substrates using CSD method.  Performance of the fuel cell was evaluated with hydrogen-air at °C.  Peak power densities of ≈90 and ≈1500 mW/cm 2 were measured at 450 and 800°C, respectively (with ≈10-micron-thick BCY electrolyte).  The main voltage drop in the fuel cell is due to electrode polarization (contribution from electrolyte resistance becomes significant as temperature decreases).  Future efforts will be focused on the electrode developments to decrease the electrode polarization.  Fuel cell power density can be increased by decreasing the electrolyte thickness.

NHA Hydrogen Conference, Long Beach, CA, May 3-6,