Pulse plating of Mn-Co alloys for SOFC interconnect applications

(Mn,Co)₃O₄ Spinel is a promising coating for SOFC interconnect applications due to its high conductivity and good chromium retention capability. Electroplating of alloys followed by oxidation offers a cost effective method to produce the desired spinels. Pulse plating is always considered as a better method than direct current (DC) plating in the formation of alloys. In this research, cyclic voltammetry is used to characterize dissolution potential of each element. Mn begins to dissolve at -1.4 V_SCE, and cobalt begins to dissolve at -0.7 V_SCE. 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 300 mA/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 Ω 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.