高温环境下合金连接体防护及其影响SOFC电堆稳定性机制

The complex working environments including the oxidizing and reducing atmospheres at high temperatures at cathode and anode sides respectively, are rather harsh to the solid oxide fuel cell (SOFC) stack components. Reduction of surface oxidation and Cr contamination from interconnect are very important to the long-term stability of planer SOFC operated at high temperatures. Recently, the proposer has exploited a novel method, which combined room temperature spraying with powder reduction technology, to prepare protective coating of interconnect with larger dimension at cathode side. The key technology of preparing the coating is solved by this simple technique. In addition, the electrodeposited coating has been developed to prepare coating at anode side. Based on the above research, the Cr corrosion and protection mechanisms will be studied in various environments under the actual application condition of the stack consisting of both oxidizing and humid reducing atmospheres at high temperatures. Element diffusion and chemical compatibility between the coating and the alloy substrate will be investigated. The mechanisms of variable oxide scale thickness at both cathode and anode sides, stack internal resistance and cycle stability induced by the different atmospheres at high temperature will be investigated. The formation mechanism and change rule of oxide scale at both sides of interconnect, and the Cr volatilization and transport process at cathode side when being the existence of vapor, different electrical current load and variational partial pressure of oxygen will be illustrated. Especially, the higher valence Cr volatilization and its deposition at the cathode side close to airflow field will be illuminated. On the basis of above studies, the influencing mechanisms of alloy interconnect on both performance and stability will be clarified, and it will provide theoretical support for SOFC stacks with excellent performance and long-term stability.

固体氧化物燃料电池（SOFC）电堆高温氧化与高温还原气氛等复杂工作环境对其部件提出了极其苛刻的要求。而防止合金连接体的表面氧化及Cr污染是保证平板SOFC长期稳定运行的关键。申请人近期通过开发的粉末还原法结合简单的室温喷涂技术，突破了大尺寸合金连接体阴极侧防护涂层制备的关键。本项目拟在此基础上结合阳极侧电镀涂层，探索两侧涂层连接体在电堆实际工作的高温氧化及高温高湿还原等环境下引起的腐蚀与防护机制。研究涂层与合金基底之间元素扩散关系及化学相容性；揭示高温不同气氛下连接体两侧氧化层厚度变化，及对电堆内阻和循环稳定的影响机制；阐明水蒸气、不同电流负载及氧分压情况下连接体两侧氧化层形成机制及变化规律，以及Cr向外挥发和传递过程，特别是阴极侧气流流场处高价态Cr挥发及在阴极沉积的过程，从而阐明合金连接体影响电堆性能及稳定性的机制，为实现高性能电堆的长期稳定运行提供理论支撑。

固体氧化物燃料电池（SOFC）作为具有广泛应用前景的绿色发电系统，其应用与发展对于实现能源的高效洁净利用、保护生态环境、满足我国日益增长的电力需求和保障国家能源安全等都具有重要意义。目前使用含Cr的铁素体不锈钢作为连接体材料。但不锈钢合金作为连接体处于高温氧化与高温高湿还原等极其苛刻环境下，当长时间工作时，连接体两侧均会生成电导率较低的氧化层并逐渐增厚，导致界面接触电阻增加，进而使电堆内阻逐渐增加。特别是阴极侧高价态Cr的生成、挥发与沉积所导致的阴极性能变化将极大地影响电堆长期寿命。因此，连接体两侧必须进行有效的涂层防护处理。本项目通过采用设计开发的粉末还原法，结合简单的室温喷涂技术成功实现大尺寸(20x20cm2)连接体阴极侧尖晶石防护涂层低成本、规模化制备，并在电堆中获得实际应用。而对于实际应用的连接体阳极侧进行电镀Ni涂层制备，并对涂层与基底作用机制进行系统研究。通过实现两侧涂层的共制备，进而为大尺寸连接体两侧涂层低成本规模化制备与应用提供全新方法与思路。通过发明制备的合金连接体阴极侧涂层，在750 ºC高温氧化环境且恒电流密度（400mAcm2-）下经过10201个小时长期稳定性测试，其面比电阻不到7毫欧平方厘米，表现出极佳的性能。模拟电堆环境（阴极侧高温氧化环境，阳极侧高温还原环境）750 ºC且恒电流密度 200mAcm2-下，两侧涂层后的合金连接体长期稳定性测试及性能分解。两侧涂层后的连接体经过1526个小时长期稳定性测试，即使经过16个高低温循环，总电阻依然较小且较稳定，不到5毫欧平方厘米。性能分解后的阳极侧电镀镍涂层表现出优异的长期及循环稳定性，经过1526个小时 16个高低温循环一直较稳定不到1.5毫欧平方厘米，阳极侧涂层表现出特别优异的性能。本项目以合金两侧涂层创新方法制备及降低成本为主线，以Cr的防护、氧化层变化、改善接触性能及提高稳定性为重点，深入研究其中所涉及的共性科学问题及作用机理，为其真正实际应用打下良好的实验及理论基础。