Date: Thursday, Jun 11th
Presenter: Dr. Xingbo Liu, Mechanical and Aerospace Engineering Department, West Virginia University
Solid oxide fuel cells (SOFCs) are promising candidates for future energy conversion systems because they have higher energy conversion efficiency than conventional heat engine systems and other types of fuel cells. However, it faces several significant technical challenges, one of which is Cr-poisoning, i.e. Cr species evaporates from interconnect and re-deposits at cathode/electrolyte interface and decreases the cell performance. Advanced coatings are needed to mitigate Cr-poisoning in SOFC systems. Mn1.5Co1.5O4 spinel is one of the most promising coatings for SOFC interconnect application due to its high conductivity, good chromium retention capability, as well as good CTE match to ferritic stainless steels. Mn/Co electrodeposition followed by oxidization is potentially a low cost method for fabrication of (Mn,Co)3O4 spinel coatings. This work looks at the co-deposition of Mn/Co alloys for this application by both DC and pulse plating methods.
Cyclic voltammetry is used to characterize dissolution potential of each element. Mn begins to dissolve at -1.4 VSCE, and cobalt begins to dissolve at -0.7VSCE. By means of pulse analysis, charge and discharge times are obtained, which are found to be much shorter than the on- and off-time applied at peak current density of 300mA/cm2. Two segments of charge periods show up at this peak current density. By comparing charge times at different peak current density, one segment can be attributed to the double layer charge and another to the uniform hydrogen bubble layer. During pulse plating, Mn content decreases with increasing off-time, and surface morphologies change from flake like structures to crystalline structures. This resulted from increased Mn dissolution into the solution and hydrogen bubble release from the coating during increased off-time. Long-term (1200 h) ASR measurements demonstrate stable ASR with slight increase. The ASR value at 40,000 h was predicted to be 0.0460 W cm2. Almost no Cr was spotted on the surface. Further, more Mn was found on the conditioned surface than the as-deposited surface which further proves faster diffusion of Mn than Cr.