直孔阳极支撑中低温固体氧化物燃料电池制备和性能研究

Solid oxide fuel cells (SOFCs) are emerging as a clean and efficient power production technology. Reducing the operation temperatures of SOFCs to intermediate-to-low temperatures (500–600C) will not only lead to the reduction of cost of cell components such as interconnectors, but also the increase of the durability and lifetime of the cells. Anode-supported planar SOFCs have attracted increasing attention among various cell configurations due to small thickness of the electrolyte layer and resultant low ohmic polarization. In this configuration, since the anode is the thickest component, significant concentration polarization may arise from it. For preparation of anode supports, tape casting technique has been widely used. In this method, substances such as graphite and starch are used as fugitive pore former. The problem with this method is that the as-formed pores are randomly distributed, and pore paths are tortuous and irregular, hindering mass transport in the anode and giving rise to severe concentration polarization. Tape casting involving phase inversion solidification step has been explored for preparation of asymmetric ceramic membranes. In this project, we propose to adopt this method for one-step forming of the anode support and functional layer. The as-prepared anode support consists of finger-like straight open pores, allowing fast transport of gaseous species and thus reducing the concentration polarization. This project is intended to investigate the phase-inversion co-tape casting of the anode support and functional layer, to analyze the internal three-dimensional structure of the anode using synchrotron radiation X-ray computed tomography, and to study the interdependence of phase inversion tape casting parameters, microstructure and the cell performance. Hopefully, the knowledge and techniques developed by this project will lead to the reduction of the operation temperature of the anode-supported SOFCs comprising thin film yttria-stabilized zirconia electrolyte to intermediate-to-low temperatures, contributing to the commercialization of the SOFCs technology.

固体氧化物燃料电池（SOFCs）能够将化学能直接转化为电能，具有高效率、零污染和无噪声等特点，是一种理想的发电装置。降低电池工作温度至中低温区（500-600C），是目前SOFCs技术的发展方向。采用多孔电极支撑的薄膜化电解质，是降低SOFCs工作温度的有效途径。目前制备多孔支撑体电极时通常采用石墨等造孔剂，孔隙无序分布，孔道弯曲，浓差极化严重。本项目提出采用相转化流延一步成型阳极支撑层和阳极功能层。该方法制备的支撑体具有独特的开放直孔结构，便于气体输运，浓差极化小，因此有望有效提高电池的性能和降低工作温度。本项目拟重点研究和发展开放直孔NiO-YSZ阳极支撑体/功能层的相转化共流延成型方法，发展阳极内部三维结构的同步辐射断层扫描和数据模拟分析方法，揭示多孔支撑体阳极的相转化制备条件-显微结构-电池性能之间的关系，为中低温SOFCs技术的发展提供科学基础和技术支撑。

固体氧化物燃料电池（Solid oxide fuel cell, SOFC）能够将化学能直接转化为电能，具有高效率、低排放、低噪声等优点，有望成为一种理想的发电技术。SOFC也可以工作在逆向模式 (solid oxide electrolyte cell, SOEC)，将电能转变为化学能。目前主流的单电池是以钇稳定氧化锆 (yttria-stabilized zirconia，YSZ)薄膜为电解质，平板状Ni-YSZ多孔金属陶瓷为支撑电极，其典型工作温度750℃。出于耐久性考虑，有必要降低电池的工作温度，但这是以降低电化学性能为代价。本项目旨在通过优化Ni-YSZ支撑电极的孔道结构改进电池在较低工作温度时的电化学性能。本项目研究和发展了多孔电极的相转化流延成型新方法，并与基于石墨造孔剂的常规流延成型法比较。前者制备的Ni-YSZ电极含有典型的指状开放直孔结构，而后者则为无序孔结构。开放直孔电极支撑的单电池Ni-YSZ|YSZ|La0.8Sr0.2MnO3--YSZ，在700oC时最大功率密度输出达到715 mW cm-2，而无序孔电极支撑的单电池只有300 mW cm-2。开放直孔单电池Ni-YSZ|YSZ|Sm0.2Ce0.8O2- |La0.6Sr0.4Co0.2Fe0.8O3- 同样显著优于无序孔单电池。在SOFC模式下测试，前者在700，650和600 ℃时的最大功率密度输出分别为1190，917和629 mW cm-2，而后者则分别仅为815，600和358 mW cm-2；在SOEC模式下测试 (温度700℃，电解电压1.3 V)，前者在低水蒸气浓度（10 vol%）时电流密度为1.01 A cm-2，相应的氢气生成速率为7.65 mL cm-2 min-1，而后者对应的电流密度仅为0.60 A cm-2，相应的氢气生成速率4.20 mL cm-2 min-1。开放直孔电极在低水蒸气浓度时没有显示出浓差极化，而无序孔电极则有严重的浓差极化。开放直孔电极的电化学极化也小于无序孔电极，这是因为其电化学反应位点充分暴露，更容易与气相物种接触,从而减小了电化学极化。本项目研究的相转化流延技术已经用于大尺寸单电池的制备，面积为10x10cm2、15x15cm2等多种规格的单电池已经用于SOFC电堆和系统层面的研发,为SOFC技术的商业化应用提供了重要支撑。