This document summarizes research into improving the ionic conductivity of calcium doped ceria for use as a solid oxide fuel cell electrolyte. Ceria was doped with varying concentrations of calcium from 2-10% using a spray drying technique. X-ray diffraction analysis showed the cubic fluorite structure was maintained with doping. Electrical characterization found that 5% calcium doping yielded the highest ionic conductivity, with grain and grain boundary conductivity dependent on dopant concentration. Scanning electron microscopy revealed the average grain size also varied with calcium concentration.

1. Relating Microstructure and Ionic Conductivity in Calcium Doped Ceria for Solid Oxide Fuel Cell (SOFC) Electrolytes
Cruz Hernandez, Materials Science and Engineering
Mentor: Will Bowman and Dr. Peter Crozier
School for the Engineering of Matter, Transport, and Energy
• A SOFC is an electrochemical
conversion device that offers an
efficiency around 85% (with
combined heat and power).
• Cerium based SOFC offer high ionic
conductivity at intermediate
temperatures (400-700oC). Ionic
conductivity can be improved by
doping with appropriate elements.
• The purpose of this research is to
study how the microstructure and
ionic conductivity are affected by
varying dopant concentrations of
calcium in ceria.
O2 + 4e- → 2O2-
Cathode
CH4 + 4O2→ CO2 + 2H2O
Anode Electrolyte
• Transmission electron micrograph of spray dried
ceria following calcination.
• A solution of nitrate precursors is sprayed into reactor at
400oC to form powder.
• Powder calcined at 800oC for 4 hours for full
decomposition.
• Calcined powder pressed at 5 kip for 5 min.
• Pellets sintered at 14000C for 24 hours.
• The XRD spectra indicate that the cubic fluorite structure
of ceria was maintained during calcium doping.
[Ca] Davg % ρ
2% 5.9μm 95
5% .97μm 94
10% 1.4μm 81
• Ceria with 2% calcium had the lowest conductivity and 5%
had the highest conductivity.
Conclusion
• Spray drying is a useful technique for
doping ceria electrolytes.
• XRD shows cubic fluorite structure for
all compositions.
• SEM analysis shows grain size
dependence on Ca concentration.
• Electrical characterization shows that
conductivity varies with Ca
concentration.
• 5% Ca doping gives highest grain and
grain boundary conductivity
25 30 35 40 45 50 55
ArbitraryUnits
2ϑ degrees
X-ray Diffraction of Ceria with 2, 5 and 10% Calcium
CaDC2
CaDC5
CaDC10
111
200
220
(c)
5μm
(b)
5μm
(a)
10μm
Filter
Hot air gun
Powder Collector Solution Sprayer
Exhaust
• Scanning electron micrographs of 2%, 5% and 10% calcium doped ceria (a-c).
• Average grain size (Davg) and % theoretical density.
-12
-10
-8
-6
-4
-2
0
2
0 0.5 1 1.5 2 2.5 3
Log(σ*T)
1000/T (1/K)
CaxCe(1-x)O(2-δ) ionic conductivity
CaDC_2
CaDC_5
CaDC_10
fcmGDC10 grain
gb2
gb5
gb10
fcmGDC10 gb
Grain
conductivity
Grain boundary
conductivity
2% Ca
5% Ca
10% Ca
GDC10 (ref)
2% Ca
5% Ca
10% Ca
GDC10 (ref)
Background and Introduction Materials Preparation by Spray Drying Results and Conclusions
Acknowledgements
We gratefully acknowledge the LeRoy
Eyring Center for Solid State Science
and the John M. Cowley Center for High
Resolution Electron Microscopy at
Arizona State University. This material is
based upon work supported by the
National Science Foundation under NSF
DMR 1308085.