喷涂电流对SOFC连接体MnCoCuFeNi高熵合金涂层性能的影响

The Effect of Atmospheric Plasma Spraying Current on the Properties of MnCoCuFeNi High Entropy Alloy Coatings for SOFC Interconnects

摘要:

固体氧化物燃料电池（SOFC）是一种高效、环保的能源转换设备。连接体作为SOFC电堆的关键核心部件，负责实现电连接、分隔阳极燃料气和阴极空气及支撑电池堆的重要作用，其性能优劣直接影响电堆系统的衰减和稳定性。铁素体不锈钢因具有良好的抗氧化性、合适的热膨胀系数等性质，而成为最具希望的连接体材料。但是，其在服役过程中存在抗氧化性能不足，以及铬挥发造成的阴极铬中毒等问题。因此，需在其表面制备一层防护涂层。尖晶石氧化物具有较高的电导率和良好的阻Cr扩散能力，被认为是最有潜力的金属连接体防护涂层材料。采用大气等离子喷涂技术，在不同的喷涂工作电流下于430不锈钢基体的表面制备MnCoCuFeNi高熵合金涂层，随后经800 ℃热转化处理，最终得到尖晶石高熵氧化物涂层。同时，系统分析了涂层在热转化过程中的相组成、表面和截面形貌、元素扩散和电性能的演变行为。结果表明：增大喷涂电流可以提高合金涂层的致密度，但也会在涂层内部生成更多的金属氧化物；经热转化处理后，Mn、Co和Cu元素优先扩散至涂层表层形成浅灰色CuO和深灰色(Mn,Co,Cu)₃O₄尖晶石氧化物，这种元素偏聚随着热转化时间的延长而逐渐均匀化。热转化初期在靠近基体/涂层界面的涂层内部形成了富Cr扩散带，但表面形成的热转化层可有效遏制Cr扩散带向外的进一步扩展。高熵合金热转化层的电导率并未受喷涂电流的影响，其最终电导率约为10.1 S?cm^-1。相反，面比电阻却随喷涂电流的增加而增大，其中涂层最佳面比电阻值（14.95 mΩ·cm²）比无涂层不锈钢的要小。通过高熵合金原位转化策略构建了兼具高导电性和Cr阻隔性能的防护涂层，为开发长寿命SOFC连接体提供了新思路。

Abstract:

Solid oxide fuel cell （SOFC） is an efficient and environmentally friendly energy conversion device， characterized by high energy density， low emissions， and silent operation. As a key core component of SOFC stack， the connector is responsible for connecting the electrode and electrolyte， establishing a good electron and ion transport pathway， and playing an important role in current collection and power release. Its performance directly affects the attenuation and stability of the fuel cell stack system， and is also one of the key technologies restricting the development of high-power， high reliability， and long-life SOFC systems in China. Ferritic stainless steel has become the most promising connector material due to its excellent oxidation resistance， suitable thermal expansion coefficient， and other properties. However， a protective coating still needs to be prepared on its surface to solve the problems of insufficient oxidation resistance and cathode chromium poisoning caused by chromium volatilization during service. This article uses different spraying working currents to prepare MnCoCuFeNi high entropy alloy coatings on the surface of 430 stainless steel substrate. Subsequently， spinel high entropy oxide coatings are obtained by thermal conversion treatment at 800 ℃. The evolution behavior of phase composition， surface and cross-sectional morphology， element diffusion， and electrical properties of the coatings during the thermal conversion process is systematically analyzed. The results indicate that increasing the spraying current can improve the density of the alloy coating， but it can also generate more metal oxides inside the coating； After thermal conversion treatment， Mn， Co， and Cu elements preferentially diffuse to the surface of the coating to form light gray CuO and dark gray （Mn， Co， Cu） 3O4 spinel oxides. The segregation of these elements gradually becomes uniform with the prolongation of thermal conversion time. In the early stage of thermal conversion， a Cr rich diffusion band was formed inside the coating near the substrate/coating interface， but the surface thermal conversion layer successfully suppressed further outward diffusion of the Cr diffusion band. The conductivity of the high entropy alloy thermal conversion layer is not affected by the spraying current， and its final conductivity is about 10.1 S?cm^-1. On the contrary， the surface specific resistance increases with the increase of spraying current， and the optimal surface specific resistance value of coated stainless steel （14.95 m Ω·cm²） is smaller than that of uncoated stainless steel. In this paper， a protective coating with both high electrical conductivity and Cr blocking performance was constructed through the in-situ transformation strategy of high-entropy alloys， which provides a new idea for the development of long-life solid oxide fuel cell （SOFC） interconnects.