Influence of sodium gluconate concentration on the microstructure of Mn–Co-CeO2 electrodeposition

The reduction in the operating temperature of solid oxide fuel cells (SOFCs) from 1000 °C to 600– 800 °C leads to the potential for using lower cost metallic interconnects materials such as stainless steel. However, excessive growth of chromia and chromium evaporation can lead to cathode poisoning, and thus shorten the required service life for the SOFC stack. In order to solve the mentioned problems, protective and conductive coatings can be employed. Manganese-cobalt coatings are promising candidates for SOFC interconnect applications because of their high conductivity and good oxidation resistance [1-3]. In the present study, the effect of sodium gluconate on the microstructure of manganese-cobalt-CeO2 was investigated. One-compartment cell was used for DC electrodeposition process. All experiments were carried out in 100 ml electrolytes prepared with deionized water. Bath electroplating with composition of 0.5 M MnSO4 + 1 M H3BO3 + 0.1 CoSO4 M + CeO2 40 g/L + 0.1 M (NH4)SO4 at pH 2 and current density of 600 mA.cm-2 was used to electrodeposition of Mn-Co-CeO2 coating. The effect of sodium gluconate concentration (NaC6H11O7) on the microstructure was characterized by means of scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDS). In order to investigate the effect of sodium gluconate in the solution, different amounts of NaC6H11O7 (0.35 M, 0.7 M and 1.4 M NaC6H11O7) in the electrolyte solution were studied. Figure1 demonstrates the surface morphology of as deposited Mn-Co-CeO2 coating in bath with different concentration of sodium gluconate. Results showed that the increase of sodium gluconate concentration caused to the increase of cathodic current efficiency. Also results demonstrated that 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 142 the variation of sodium gluconate concentration had significant effect on the grain size, uniformity and adherence of the coating. Based on the EDX results at low amount of sodium gluconate (0.35 M) the amount of manganese was low. It is because of low chelating agents to chelate with manganese [2]. At higher amount of sodium gluconate (1.4 M and higher) the amount of cobalt, manganese and oxygen was not very different from 0.7 M gluconate. So 0.7 M gluconate in the electrolyte solution is sufficient for obtaining approximately equal amount of manganese and cobalt in the coating composition. Also the grain size in 1.4 M gluconate is larger than 0.7 M which probably one causes of growing such coarse grains, is the higher deposition rate. Such relative coarse grains obtained from 1.4 M sodium gluconate solution is harmful during SOFC operation [4].