利用熔盐歧化反应制备Nb掺杂TiO2涂层及其抗腐蚀与导电性能

Stainless steels have been considered as the most promising materials for the interconnects of intermediate-temperature solid oxide fuel cell(SOFC) and the bipolar plates of proton exchange membrane fuel cell. However, the main obstacles for using stainless steel interconnects of SOFC are the increase of area specific resistance due to the growth of oxide scales and the poisoning of cathodes due to volatile Cr, and that for using stainless steel bipolar plates of PEMFC are the dissolution and passivation. Applying corrosion resistant and electrically conductive coatings is an effective method to overcome these problems. In view of the fact that n-type TiO2 exhibits high chemical stability, it is proposed in this project that high-valence Nb5+ is introduced to dope TiO2, with an attempt to increase its electronic conductivity and high temperature oxidation resistance. Thereby,a Ti-Nb alloy layer would be prepared innovatively by using disproportionation reaction in molten chlorides, followed by heat treatment in a low oxygen pressure environment and in air to obtain Ti1-xNbxO2 coatings, respectively. Furthermore, the corrosion behavior and electrical conductivity of the alloy with and without coatings will be investigated in the simulated cathode and anode atmospheres of both SOFC and PEMFC, and its microstructures will also be examined, in an attempt to understand the affecting mechanism of the coating and Nb in improving the corrosion resistance and electronic conductivity.This investigation is of great significance to the development of new corrosion resistant and electrically conductive coatings for stainless steel interconnects or bipolar plates of fuel cells.

不锈钢被认为是有希望的中温固体氧化物燃料电池(SOFC)连接体和质子交换膜燃料电池(PFMFC)双极板材料。然而，不锈钢连接体在SOFC环境中面临着合金表面氧化物的生长而导致的面比电阻增加和Cr挥发导致的电池阴极中毒等问题，在PEMFC环境中则面临着溶解与钝化问题。施加抗腐蚀、导电涂层是解决上述问题的一种有效途径。鉴于TiO2的高化学稳定性，本项目拟通过掺杂高价态的Nb5+来提高其电导率与抗高温氧化性能，从而制备Nb掺杂的TiO2涂层。为此，创新地利用熔盐歧化反应在430不锈钢表面制备Ti-Nb合金，分别通过在高温低氧压环境和空气中的氧化处理使合金层转化为Ti1-xNbxO2涂层。研究合金/涂层在模拟SOFC/PEMFC阴、阳极环境中的腐蚀行为与导电性能，表征合金/涂层的微观结构，阐明涂层与Nb的作用机制。本研究对于发展新的不锈钢连接体/双极板用表面防护涂层与制备技术具有积极的意义。

作为有希望的燃料电池连接体或双极板材料，不锈钢在燃料电池环境中存在抗腐蚀性能不足和接触电阻增大等问题。施加抗腐蚀、导电涂层是解决上述问题的一种有效途径。鉴于TiO2具有高化学稳定性，但导电性差,本项目拟利用高价态Nb5+的掺杂发展具有良好抗腐蚀与导电性能的Ti1-xNbxO2涂层。因此，项目拟利用熔盐歧化反应在430不锈钢(430SS)表面制备Ti-Nb合金，通过高温氧化处理得到Ti1-xNbxO2涂层，并研究其高温氧化性能与导电性能。进一步利用熔盐歧化反应制备了铌的氮化物涂层,并研究了其在模拟质子交换膜燃料电池环境中的抗腐蚀与导电性能。此外，也尝试利用熔盐歧化反应制备TiC和NbC纳米粉体。.在熔融NaCl-KCl-K2TiF6-Ti和NaCl-KCl-NaF-NbCl5-Nb中，Ti(II)和Nb(IV)离子在430SS表面歧化形成的Ti和Nb原子与基体中的氮反应分别形成致密、粘附性良好的纳米晶TiNx和β-Nb2N涂层,但难以实现Ti和Nb的共沉积。通过分别沉积Nb、Ti和Nb，在430SS表面制备了三层结构的β-Nb2N/TiN/Nb6O涂层。经氧化处理后在430SS表面形成了粘附性良好的外层为Ti1-xNbxO2，内层为相对富Cr的双层结构氧化层。涂层没有提高430SS在800℃空气中的抗氧化性能，但有效降低了其面比电阻。.制备的纳米晶β-Nb2N涂层具有高的化学稳定性，能显著提高430SS在模拟PEMFC环境中的抗腐蚀性能，并降低接触电阻。.金属钛粉可溶解于熔融NaCl-KCl中形成Ti(II)离子，Ti(II)离子在乙炔黑、多壁碳纳米管以及石墨烯表面发生歧化反应形成的钛原子与碳原子反应最终分别形成零维、一维和二维结构的高纯TiC纳米粉体；在加有Nb粉和乙炔黑的熔融NaCl-KCl中难以合成NbC纳米粉体。但当进一步加入NbCl5后，能合成高纯NbC纳米粉体， 这是由于Nb(V)与Nb反应形成的Nb(IV)在乙炔黑表面发生歧化反应形成的Nb原子与碳原子结合形成NbC。.本研究对于发展新的不锈钢连接体/双极板用表面防护涂层与过渡金属碳化物纳米粉体制备理论与技术具有积极的意义。.