Development of a multi-component aqueous NiO, CuO, and Co3O4 suspension for use in suspension plasma spraying of SOFC anode layers

For the purpose of suspension plasma spraying solid oxide fuel cell anode coatings, individual and multi-component aqueous suspensions of NiO, CuO, and Co3O4 have been assessed for stability either alone or in conjunction with poly(ethylenimine) (PEI) or 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA). Optimum concentrations of the dispersants have been determined using rheology measurements. The suspensions have also been characterized by dissolution behavior and zeta potential. The isoelectric points of CuO, Co3O4, and NiO were measured to be 7.9, 7.4, and greater than 10, respectively. Both the Co3O4 and a fine NiO fraction were stable in their native state. Based on the results of this study, all of the metal oxides respond favorably to PBTCA as a dispersant, while only the Co3O4 responds well to the addition of PEI. The effectiveness of PEI as a dispersant for CuO is unclear. A multi-component suspension of these oxides containing the equivalent of 60 wt.% Cu, 32 wt.% Co and 8 wt.% Ni using only PBTCA as a dispersant showed no obvious signs of settling over 2 days at a pH of 8.5.