PNNL-13501 - Pacific Northwest National Laboratory

Ultrathin Electrolyte Test Results
——
5 µm
Figure 2. Scanning electron micrographs of representative dense sputtered yttria-stabilized zirconia electrolyte layers
incorporated into fuel cell stacks. The less porous electrode layers are the nickel/zirconia cermet substrates on which the
sputtered yttria-stabilized zirconia was deposited. The air-side (high porosity) electrodes were screen printed on the yttriastabilized
zirconia after its deposit.
The initial cell test was conducted at 800°C with
200 sccm flow of hydrogen with 3% water. The plot of
cell voltage and power as a function of current density is
shown in Figure 3. The open circuit voltage was near
1 volt, which is near the theoretical value of 1.1 indicating
a dense, pore-free electrolyte. The slightly lower than
theoretical open circuit voltage is probably due to a leaky
cement seal. The cell performance is lower than
expected. At 800°C the losses of the 5 µm electrolyte
would not be noticeable, and therefore the low
performance is probably due to poor electrodes. An
improved cathode of strontium-doped lanthanum ferrite
showed an increase in performance over the initial
manganite cathode. The performance of the improved
cell is shown in Figure 4. Additional performance
improvement may be gained through the modification of
the anode electrode.
Cell Performance Test
0 0.2 0.4 0.6 0.8 1
1.2
0.2
0.18
1
Voltage(V)
Power
0.16
0.8
0.14
0.12
0.6
0.1
0.08
0.4
0.06
0.2
0.04
0.02
0
0
0 0.2 0.4 0.6 0.8 1
Current Density (A/cm2)
Figure 3. The plot of cell voltage and power as a function of
current density
332 FY 2000 Laboratory Directed Research and Development Annual Report
Improved Cathode
0 0.2 0.4 0.6 0.8 1
1
0.9
0.8
0.7
0.6
0.5
A/cm2
0.4
0.3
0.2
0.1
0
W/cm2
0 0.2 0.4 0.6 0.8 1
Current Density (Amps/cm^2)
Figure 4. The plot of cell performance with improved
cathode
Summary and Conclusions
——
5 µm
Ultrathin (less than 10 µm) yttria-stabilized zirconia films
were produced by reactive sputtering for testing as
electrolyte layers in solid oxide fuel cells applications.
By depositing the electrolyte films at elevated
temperatures (600°C) and low pressures (≤ 2.5 m torr),
high-density zirconia coatings having a tetragonal
structure were produced. Preliminary tests of solid oxide
fuel cells incorporating the sputtered electrolyte coatings
indicated less than optimal performance, although this
was probably related to electrode rather than electrolyte
issues.
0.25
0.2
0.15
0.1
0.05
0