SOFC SwiderLyons Aug08b.ppt

ONR Industry Day 11 August 2008 Dr. Karen Swider Lyons Naval Research Laboratory, Washington DC Karen.lyons@nrl.navy.mil

(202) 404-3314

Topics

Beware of new materials!

EXAMPLE: single phase mixed ionic-electronic conductors (MIECs)

Project goal: compare dime cells with various LN-containing cathodes Compare to YSZ/LSM composite cathodes.

Single MIEC does not work well - works better as composite C. Laberty, F. Zhao, K. Swider-Lyons, and A. Virkar, “High Performance Solid Oxide Fuel Cell Cathodes with Lanthanum-Nickelate-Based Composite” Electrochemical and Solid State Letters, Vol. 10, B170-B174 (2007) Cell with LN-only cathode: 0.3 W cm-2 Cell with LN/SDC cathode: 2.2 W cm-2 Better than 1.8 W cm-2 for similar cell with YSZ/LSM cathode SDC is a good ionic conductor LN is a good MIEC, but not good enough

Cell-level challenges for SOFC performance Microstructural effects

Chemical effects

Single cell data does not match stack data What looks good in isolation can ruin a system

CPOX Issue: Loss of power density with air dilution

Jiang and Virkar, 2003 2 A cm-2 with 100% H2

1.3 A cm-2 with 50% H2-50% N2

0.7 V

New issues with fuel utilization when using Cu/CeO2 “direct oxidation” catalysts

Problem with unreacted methane only observed after building a small stack that operated at high current density Button cell measurements miss subtleties of fuel utilization

Prepare for Power Transients Military systems are required to operate in a wide range of conditions More dynamic systems are more useful If you don’t run transient tests on your systems, the military will Real load data measured at NRL on a propulsion system (battery)

0.20 0.21 pO2 = 0.21 0.16 pH2 = 0.89 0.26 pH2O = 0.11 0.75 During operating, cells are far from uniform Oxygen and hydrogen depleted along cell, steam increases Gradients of reactants in operational cells Example: Siemens Westinghouse flat-tube high power density SOFC Modeling by Lu, Schaefer and Li, J. Power Srcs 2004.

anode electrolyte cathode

Cells have wide temperature variations 936 to 1042 °C at 300 mA cm-2 1031 to 1183 °C at 500 mA cm-2

Mechanical challenges of high temperature operation

.043” (1.08)

.040” (1.02)

.037” (0.94)

.040” (1.02)

.044” (1.12)

.046” (1.17)

.048” (1.21)

.046” (1.17) in” (mm) Cathode Interconnect Anode Interconnect

MEA

CC

CC

Measurements of separation distance between electrodes and interconnects Frame Cathode warpage: 0.006” Anode warpage: 0.002”

Carbon thermodynamics

Carbon deposition can occur during transients, and create cold and hot spots Ko, et al, “Thermodynamic Analysis of Carbon Deposition and Electrochemical Oxidation of Methane for SOFC Anodes,” Electrochem. Solid-State Lett., Volume 4, Issue 2, pp. A12-A15 ( 2001)

Last but not least

Build it early

- your system will not work on the last day of the program

Think ahead to avoid surprises from