SOFC不锈钢连接体用稀土改性MnCo2O4尖晶石涂层的电沉积制备及高温性能研究

Ferritic stainless steels have been considered as the most promising materials for the interconnects of intermediate-temperature solid oxide fuel cell (SOFC). However, the increase of area specific resistance due to the growth of oxide scales and the poisoning of cathodes due to volatile Cr during SOFC operation limit its application. An effective method to overcome these problems is to apply oxidation resistant and electrically conductive coatings. Due to its excellent comprehensive properties, MnCo2O4 spinel coating becomes the most promising candidate for the protection of stainless steel interconnects of SOFC. Electrodeposition method is an advantageous novel method for preparing MnCo2O4 coatings. This method offers a more economical and efficient technique for spinel coating fabrication, and can be applied on substrate with complex geometry shape. However, due to the great difference in the electrodepositon potentials of Co and Mn, pores, cracks and inhomogeneous composition distribution are easliy to occur in the Mn-Co coating. Accordingly, in this study electrodepositon of Mn-Co composite coatings will be prepared on a ferritic stainless steel, with EDTA as complex agent and chloride system as electroplating bath, followed by heat treatment to obtain MnCo2O4 spinel coatings with dense microstructure and good joining strength. On this basis, composite electrodepositon of Ce and Dy-modified Mn-Co spinel coatings will be prepared, with an attempt to further suppress the growth of the Cr2O3-rich scale under MnCo2O4 coating. Furthermore, the high temperature oxidation behavior and electrical conductivity of MnCo2O4, Ce and Dy-modified Mn-Co spinel coatings will be investigated in simulated SOFC cathode atmosphere, and its microstructures will also be characterized, in an attempt to understand the mechanism of Ce and Dy in improving the oxidation resistance and electronic conductivity. This investigation is of great theoretical and practical significance to the development of oxidation resistant and electrically conductive coatings for stainless steel interconnects of SOFC.

铁素体不锈钢是最具应用前景的中温固体氧化物燃料电池(SOFC)连接体材料，但也面临着合金表面氧化物生长导致的面比电阻增加及Cr挥发引起的电池阴极中毒等问题。施加导电抗氧化涂层是解决上述问题的一种有效途径，其中以Mn-Co尖晶石涂层最具应用前景。电镀法是一种简单、成本低、可在形状复杂工件上实施的涂层制备技术，但由于Co和Mn沉积电位差大，镀层易出现孔洞、裂纹及成分不均现象。为此，本项目拟采用以EDTA为络合剂的氯化物溶液电沉积Mn-Co合金层，经氧化处理获得致密、与基体结合良好的MnCo2O4涂层，进一步为抑制MnCo2O4涂层与基体间富Cr2O3膜的生长，采用复合电镀技术制备Ce和Dy掺杂MnCo2O4涂层，研究合金/涂层在SOFC环境中的高温氧化行为及导电性能，阐明Ce、Dy作用机制。本项目对于发展具有实用化前景的SOFC不锈钢连接体用导电抗氧化涂层具有积极意义。

铁素体不锈钢是最具应用前景的中温固体氧化物燃料电池(SOFC)连接体材料。然而铁素体不锈钢在SOFC环境中存在抗高温氧化性能不足导致的面比电阻增大以及Cr挥发引起的阴极中毒问题，造成电池性能下降甚至失效。施加导电抗氧化涂层是解决上述问题的一种有效途径。部分无Cr尖晶石涂层具有高温稳定性良好、电导率和热导率较高、与铁素体不锈钢热匹配良好等优点，有望成为SOFC不锈钢连接体用防护涂层。本项目采用复合电沉积技术在不锈钢表面预沉积CeO2和Dy2O3掺杂的Mn-Co合金镀层，再经氧化处理获得稀土掺杂MnCo2O4涂层，研究合金/涂层在SOFC环境中的高温性能及其作用机制。在此基础上拓展研究Cu-Co尖晶石和Ni-Fe尖晶石涂层的制备及其高温性能。主要研究结果如下：.1）选用EDTA作为络合剂，在氯化物溶液中（0.05M EDTANa2 + 0.05M CoCl2 + 1.25M MnCl2 + 30g/L NH4Cl + 20g/L NH4Br）电沉积Mo-Co合金，获得优化电镀工艺参数：pH为4.5、电流密度125 mA cm-2、电镀前喷砂处理表面、电镀过程中磁力搅拌。在该工艺基础上，向镀液中分别加入6 g/L CeO2和5g/L Dy2O3纳米粉，获得稀土掺杂Mn-Co合金涂层，最终经适宜的氧化处理工艺获得CeO2和Dy2O3掺杂的Mn-Co尖晶石涂层。两种稀土元素掺杂均可以提高Mn-Co涂层的抗氧化性能，有效抑制Cr元素的外扩散及富Cr氧化膜的生长，体现了良好的掺杂改性效果。.2）在柠檬酸盐溶液中电沉积Cu-Co合金，获得优化电镀工艺参数，揭示电沉积机理。当电沉积时间较少时，在800 ℃空气中长期氧化后涂层转变为单一的(Co,Cr,Cu,Mn,Fe)3O4相；延长电沉积时间，涂层经高温氧化最终转变为氧化铜/钴基尖晶石复合涂层。两种涂层均体现出良好的高温抗氧化性能和电性能，但后者具有更好的抑制Cr外扩散的能力。.3）Ni-Fe涂层样品长期氧化后合金/涂层界面形成大量孔洞，掺杂CeO2及施加CrNx扩散障均可以显著抑制界面孔洞，且有效提高Ni-Fe尖晶石涂层的高温性能。. 本研究对于推动SOFC不锈钢连接体的实用化进程具有实际意义。