Chapter 12. Summary and Conclusions [chapter]

The Historicity of the Patriarchal Narratives  
Two fabrication techniques were investigated as they pertain to the assembly of advanced solid oxide fuel cells. Polymer sphere lithography has been utilized to create two-dimensional metallic networks on fuel cell electrolyte materials. Although the fabrication process involves somewhat imprecise, random elements, the experimental variation from the expected geometries is extremely small. Under fuel cell operating conditions, the structures, and, hence, the 3PB and 2PB area fraction values,
more » ... fraction values, exhibit remarkable high temperature stability. These well-defined and well-behaved electrode structures access a wide range of 3PB regimes, lending themselves to future mechanistic studies on electrolyte-electrode material systems, as well as providing a strong experimentally correlated basis for computational modeling. Beyond mechanistic studies, these anti-dot structures have served as platforms for fabrication of three-dimensional electrodes. The cathodic electrochemical deposition of undoped and Sm-doped ceria has been developed in templated and template-free configurations to produce a variety of tunable anode microstructures. The strictly chemical nature of the deposition step allows these electronically insulating coatings to deposit onto non-conducting areas of substrates, insofar as they are close enough to an exposed metal surface. The end result is ubiquitous CeO 2 coatings on thin, porous metallic networks overlaid onto YSZ/porous metal substrates, with quality metal|CeO 2 and YSZ|CeO 2 interfaces, which are morphologically 151 stable at high temperatures and reducing atmospheres. Deposition was also definitively shown to occur on two MIEC, fuel cell cathode materials-BSCF and SCN. To probe the activity of CELD Sm-doped ceria anodes, detailed, morphologicallydriven ACIS analyses were conducted, revealing two co-dominant, resistive processes for metal network embedded configurations. The LF arc was determined to be surfacerelated; the HF arc was determined to be configurationally related, in particular to the resistance of electron migration through the SDC deposit on top of the metal regions, and the resulting restriction of the field lines to the nominal 3PB region. The LF arc was therefore taken to represent the true measure of surface activity for CELD ceria. The lowest extrapolated ASR values for this arc were shown to be in the range of 1.3 -6.8 mΩ cm 2 at 650 °C in 97% H 2 and 3% H 2 O. 152 Appendix A ImageJ Analysis Details The following describes the analytical approach to identifying and characterizing the pores of the anti-dot networks using the ImageJ software described in Chapter 2. The process is briefly illustrated in Fig. A.1 . First, an as-taken grayscale SEM image is imported into ImageJ (Fig. A.1a) ; then, the data bar region is cropped and the rest of the image is converted into a true black-and-white image (Fig. A.1b) . The ImageJ user can define a grayscale threshold cutoff value, above which the associated pixels are converted to purely black, and below which the pixels are converted to purely white. Consequently, the ideal SEM image to be analyzed is one where there is significant grayscale contrast between the circular pores exposing the electrolyte surface, and the metal network lying on top. Secondary electron imaging mode was chosen owing to its inherent contrast associated with topographical features (recall that the metal network is 200-400 nm thick). Back-scattered mode, which provides elemental materials contrast, added anywhere from 5-15% areal error due to pore shading; and in-lens mode, known for its high contrast imaging ability, was found to provide inconsistencies related to charging effects from the non-conducting YSZ. Care was taken to provide qualitatively consistent contrast in the SEM images across the entirety of the substrate, to ensure accurate and uniform threshold application. The resulting image (Fig.A.1b) is now a mixture of connected and disconnected black objects, which ImageJ can identify automatically. Problems arise, however, due to dark pixels that are not pore-related. The smaller dark objects can be automatically removed, and the image consequently cleaned up, as in Fig. A.1c . However, the messy, 157
doi:10.1515/9783110841442-013 fatcat:chdznzr3brbwhisgumirukhttm