Biomass carbon fueled solid oxide fuel cells with liquid antimony

2016/1/25
Biomass carbon fueled solid oxide fuel
cells with liquid antimony anode
Nanqi Duan and Jian Li*
Huazhong University of Sci. and Tech.
Presented to Curtin-UQ Workshop on Nanostructured
Electromaterials for Energy
Jan. 18, 2016
DC-SOFCs
Advantages
Normal component
Key issues
Low electrochemical performance
High theoretic efficiency
ΔG/ΔH >1
Oxygen ions only available at around
anode/electrolyte interface
Abundant resources: coal,
biomass, nature gas
Easy CO2 capture
Improvement
approaches
Carbon transport
Oxygen ion transport
Key reaction
C(s) + 2O2- → CO2 (g) + 4e-
Gür et al, (2010) J. ECS 157(5): B751-B759, (2013) Chemical Reviews 113(8): 6179-6206.
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DC-SOFCs with liquid metal anodes
Low melting point metals
(e-)
Metal
OO2-
(-)
Electrolyte
Anode (MO )
x
(e-)
Air
(+)
Cathode
Metal
Melting
point (K)
Melting point
of oxides (K)
OCV at 973
K (V)
Sn
505
1903
0.93
0.83
In
430
2190
Bi
544
1090
0.48
Pb
601
1161
0.60
Sb
904
929
0.75
Liquid Sb anode DC-SOFC
Cathode: O2 + 4e- → 2O2Anode: 4/3Sb(l) + 2O2- → 2/3Sb2O3(l) + 4eC(s) + 2/3Sb2O3(l) → 4/3Sb(l) + CO2(g)
Overall reaction: C(s) + O2(g) → CO2(g)
Tubular DC-SOFC with liquid Sb anode
Cell fabrication
Cell pictures
Testing set up
8YSZ powders, Binders
Ethyl alcohol
Ball milling
8YSZ Slurry
Casting
Demolding
8YSZ substrate tubes
Sintering
8YSZ support tubes
Dip-coating
cathode and
sintering
8YSZ supported cells
Duan N‐Q et al, Sci. Rep. 2015;5 (doi:10.1038/srep08174); Energy 2016;95:2748. 2
2016/1/25
Electrochemical performance I: no carbon fuel
EIS & I-V-P curves
Cell reactions
Cathode: O2 + 4e- → 2O2Anode: 4/3Sb(l) + 2O2- → 2/3Sb2O3(l) + 4eOverall reaction: 4/3Sb(l) + O2(g) → 2/3Sb2O3(l)
SEM micrograph and EDS analysis of tested cell
800 ºC
Duan N‐Q et al, Energy 2016;95:2748 (doi:10.1016/j.energy.2015.10.033)
Electrochemical performance II: carbon added
EIS spectra(a) and I-V-P
curves (b) of Cell C at
original and after refueling
Cell with different amounts of carbon fuel working at
800 ºC at a constant current density of 0.4 A cm-2
Duan N‐Q et al, Energy 2016;95:2748 (doi:10.1016/j.energy.2015.10.033)
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Possible anode reactions
Ideal reaction
C(s) + 2/3Sb2O3(l) → 4/3Sb(l) + CO2(g)
Gibbs free energy vs. temperature
Side reactions
CO2(g) + C(s) → 2CO(g)
Sb2O3(l) + 3C(s) → 2Sb(l) + 3CO(g)
Sb2O3(l) + 3CO(g) → 2Sb(l) + 3CO2(g)
 Cell performance depends on Sb2O3
reduction by carbon fuel and
temperature.
 Fuel properties and working
conditions make a big .
Higher temperature leading more
CO generation, lowering the fuel
utilization and energy conversion
efficiency.
Two biomass carbon fuels
CAC (cocoanut active charcoal) and PCS
(pyrolyzed corn starch)
Both are amorphous, and the ID/IG for CAC is larger
(0.98) than that for PCS (0.80.
SEM micrographs CAC (a) and PCS (b)
Duan N‐Q et al, Applied Energy 2016 4
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Anode exhaust gas analysis
Exhaust gas analysis
Testing set-up
Time and temperature dependences of produced CO and CO2 amounts and
CO/CO2 ratio: CAC (a) and PCS (b). CO/CO2 ratio reflects the degree of
carbon oxidation; and a larger ratio value corresponds to a lower degree of
carbon oxidation and a shorter period of stable running time per gram of
carbon fuel
Duan N‐Q et al, Applied Energy 2016 Cell performance fueled with CAC and PCS
a
No fuel
Performance at 750 and 800 oC
c
PCS
b
CAC
d
Duan N‐Q et al, Applied Energy 2016 5
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Efficiency analysis
2
Uf  3
1
( M  M ')  M '
3
2
3
Itg M C
Uf 
4eNA
M
It m
2
1
(M  M ')  M '  g
3
3
6eNA
m
M
MC
mtg

 0
IV  t  dt
-H
Cells
m
(g)
CAC at 800 °C
1.956
PCS at 800 °C
m
MC
I is the work current, m is the real
weight of added carbon fuel at
testing temperature, MC is the molar
mass of carbon, e is the electron
charge and NA is the Avogadro
constant, V(t) is the working voltage
as a function of testing time and ΔH
is the molar enthalpy change of
carbon oxidation
Fuel utilization
(Uf)
Electrical
efficiency (η)
5.6
51.4%
26.4%
1.558
7.1
65.7%
33.8%
CAC at 750 °C
1.958
7.2
65.4%
28.9%
PCS at 750 °C
1.570
~0.6
6.0%
5.3%
Time per gram
(tg) (h g-1)
Conclusions
1) Sb2O3 formed at the interface of electrolyte and liquid antimony and then
immigrated away because of a lower density. Separation feasibility of Sb and
Sb2O3.
2) Cell performance can be recovered to the original level by refueling. By this
way, the cells works like a rechargeable battery.
3) Biomass carbon CAC, with low degree of graphitization, possesses higher
activity than PCS at 750 oC for Sb2O3 reduction and more CO generated. PCS
with high degree of graphitization has more advantages at higher temperature.
4) The electrical efficiency of YSZ-supported cells with liquid Sb anodes is
relatively lower than that of conventional SOFCs.
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Acknowledgements
This work was funded by National “863” and NSFC projects, and conducted by Nanqi Duan
who is currently a Ph. D. candidate in the Center for Fuel Cell Innovation.
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