(157g) Micro-Structural Optimization of MoO2-Based Anode for SOFC Applications

Authors: 
Kwon, B. W., Washington State University
Marin-Flores, O., Washington State University
Norton, M. G., Washington State University
Ha, S., Washington State University



Micro-structural
optimization of MoO2-based anode for SOFC applications

Byeong Wan Kwona, Oscar Marin-Floresa,b,
M. Grant Nortonb, Su Haa

aThe Gene and Linda Voiland School of
Chemical Engineering and Bioengineering, Washington State University, Pullman,
WA 99164

bSchool of Mechanical and Materials Engineering,
Washington State University Pullman, WA, 99164-2920

Solid oxide fuel cells (SOFCs), which typically run at
temperatures in the range of 600-1000°C, can be operated with a variety of fuels, such as liquid hydrocarbons and
synthetic liquid bio-fuels. The SOFCs are composed of a solid dense electrolyte
sandwiched by two electrodes, an anode and a cathode. These electrodes should
have a proper porosity to allow an efficient transport of both the reactants
and byproducts, while possessing a proper sintering to allow high ionic and
electronic conductivities. Therefore, their optimized micro-structures can lead
to improve overall performances of SOFCs.

Recently,
our group has successfully fabricated a novel MoO2-based anode for
the SOFC application and operated it with both the model aviation fuel and
bio-diesel. In this study, we have improved the overall performance of our MoO2-based
SOFC by controlling the micro-structure of the MoO2-based anode
using a pore former such as a polyvinyl alcohol (PVA). Typically, MoO2-based
anodes were manufactured using MoO2 nanoparticles to forma seed
layer structure with an average thickness of 8 µm via electrostatic
spray deposition (ESD) method. Over this seed layer, additionally catalyst inks
containing both MoO2 and different concentrations of PVA were
painted to determine the effect of PVA concentration on anode morphology and
power density output. We have utilized n-dodecane as a model fuel to assess the
performance of SOFCs. The power density value at 0.6V improves from 540mW cm-2
to 2,168mW cm-2 as the PVA concentration increases from 6wt% to 12
wt%. However, further increasing the PVA concentration up to 21wt% decreases
the power density output. Hence, the PVA concentration greatly influences the
cell performance and a 12wt% PVA seems to be the optimum concentration that
leads to the best micro-structure of the MoO2-based anode. As
observed in SEM images of 24h tested cells, the anode structure with a low PVA
content of 6wt% is much denser compared to the ones with a higher PVA content,
which can be attributed to a deficit amount of PVA required to produce a proper
micro-porous structure in the anode. Therefore, a low porosity in the anode
significantly limits mass transfer process, which leads to a larger anode
overpotential (i.e., a larger anode charge transfer resistance from the
impedance measurements) and lower power density output. Hence, the PVA
concentration plays an important role in the performance and morphology of MoO2-based
anode. The MoO2-based SOFC with the optimized micro-pore structure
also showed a very stable performance over 24h test without showing any coking.
Under the similar operating conditions used for the MoO2-based SOFC,
the commercial Ni-based SOFC showed a much lower initial performance and deactivated immediately due to the anode coking.