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A new family of electrolytes based on Na1/2Bi1/2TiO3 for intermediate-temperature solid oxide fuel cells

用于中温固体氧化物燃料电池的基于 Na1/2Bi1/2TiO3 的新型电解质系列

基本信息

批准号：
EP/L027348/1
负责人：
Derek Sinclair
金额：
$ 60万
依托单位：
University of Sheffield
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2014
资助国家：
英国
起止时间：
2014 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FL027348%2F1
关键词：
new family electrolytes based Na1

项目摘要

A Solid Oxide Fuel Cell (SOFC) is an electrochemical device similar to a battery in that it consists of a cathode, anode and an electrolyte. They are solid-state devices where all components are ceramics and the electrolyte is an oxide-ion conductor. They operate at high temperatures (typically ~800C) where an electrochemical reaction converts fuel (eg H2, natural gas, biofuels) and air into electricity without combustion. They represent a leading direction for future power generation as they offer higher energy conversion efficiency (>60%) than conventional combustion engines (~30%) and lower pollution. Unfortunately, such high operating temperatures are costly and create engineering challenges such as long term sealing and durability of SOFCs. As a consequence, there is a drive within the SOFC community to reduce the operating temperatures to 500-700C (so called Intermediate Temperature SOFCs, ITSOFCs) to overcome the engineering challenges and reduce costs to produce clean, reliable and affordable energy. This requires the development of new electrolytes with high oxide-ion conductivity that can operate under the harsh operating conditions of simultaneous exposure to fuel and air at >500C. Rare earth (RE) stabilised d-Bi2O3 (eg RE=Er, ESB) are excellent solid electrolytes and offer sufficiently high oxide-ion conductivity at 500-700C in air but decompose under reducing conditions. One of the highest performances of an ITSOFC has been achieved using the concept of an electrolyte bilayer based on two oxide-ion conducting ceramics, Gadolinia-doped ceria (GDC) and ESB. Although the conductivity of GDC is lower than ESB it is chemically stable under reducing conditions. In this design, the GDC layer is placed at the heavily reducing anode (fuel) side to minimise the decomposition of ESB and the ESB layer is placed at the cathode (air) side. This provides a stable electrolyte with high ionic conductivity; however, preparation of such a bilayer requires a thin film deposition technique which is costly and impractical for mass production.Recently, we discovered high levels of oxide-ion conductivity in a well-known perovskite (Na1/2Bi1/2TiO3, NBT; Nature Materials, in press) and that chemical doping of Mg for Ti to increase the concentration of oxygen vacancies further enhanced the oxide-ion conductivity. Mg-doping has two other important advantages: Mg-NBT is chemically stable under reducing (fuel) conditions at 550 C and the sintering temperature of ~950C to obtain dense ceramics is similar to that of ESB and other d-(Bi,RE)2O3 electrolytes. Tape casting is a well-known technique for mass production of thick film ceramics at low cost. It is not possible to prepare GDC/ESB bilayers by tape casting followed by co-sintering due to the large difference in sintering temperature for GDC (~1350C) and ESB (~900C) ceramics; however, this should be possible for doped-NBT/ESB ceramics.The aims of this project are two-fold. First, to optimise the electrolyte properties of a newly discovered family of oxide-ion conductors based on the polar perovskite NBT. Second, to test the suitability of NBT-based materials as an electrolyte component in ITSOFCs based on bilayer electrolytes. The first aim will be achieved by undertaking systematic chemical doping studies of NBT followed by crystallographic, microstructural and electrical characterisation of doped-NBT ceramics. This will provide a comprehensive understanding of the structure-property-composition relationships of oxide-ion conductivity in this family of materials. To achieve the second aim, electrolyte bilayer ceramics will be produced by co-sintering tape-cast layers of doped-NBT and d-(Bi,RE)2O3 at temperatures < 1000C and their electrical and chemical performance tested under the conditions required for ITSOFCs. This will provide a proof-of-concept application of these materials in ITSOFCs based on bilayer electrolytes prepared by industry-standard tape casting technology.

固体氧化物燃料电池 (SOFC) 是一种类似于电池的电化学装置，由阴极、阳极和电解质组成。它们是固态设备，所有组件都是陶瓷，电解质是氧化物离子导体。它们在高温（通常约为 800C）下运行，其中电化学反应将燃料（例如氢气、天然气、生物燃料）和空气转化为电能，而无需燃烧。它们代表了未来发电的主导方向，因为它们比传统内燃机（约 30%）具有更高的能量转换效率（>60%）并且污染更低。不幸的是，如此高的工作温度成本高昂，并且带来了工程挑战，例如 SOFC 的长期密封和耐用性。因此，SOFC 界迫切希望将工作温度降低至 500-700C（所谓的中温 SOFC、ITSOFC），以克服工程挑战并降低成本，从而生产清洁、可靠且经济实惠的能源。这就需要开发具有高氧化物离子电导率的新型电解质，该电解质可以在同时暴露于 >500C 的燃料和空气的恶劣操作条件下运行。稀土（RE）稳定的d-Bi2O3（例如RE=Er、ESB）是优异的固体电解质，在500-700C空气中提供足够高的氧化物离子电导率，但在还原条件下分解。 ITSOFC 的最高性能之一是使用基于两种氧化物离子导电陶瓷、氧化钆掺杂二氧化铈 (GDC) 和 ESB 的电解质双层概念实现的。尽管 GDC 的电导率低于 ESB，但它在还原条件下具有化学稳定性。在此设计中，GDC 层放置在强还原性阳极（燃料）侧，以最大限度地减少 ESB 的分解，而 ESB 层放置在阴极（空气）侧。这提供了具有高离子电导率的稳定电解质；然而，这种双层的制备需要薄膜沉积技术，该技术成本高昂且不适合大规模生产。最近，我们发现众所周知的钙钛矿（Na1/2Bi1/2TiO3，NBT；Nature Materials，待出版）中具有高水平的氧化物离子电导率，并且对钛进行镁化学掺杂以增加氧空位的浓度进一步增强了氧化物离子电导率。镁掺杂还有另外两个重要优点：Mg-NBT 在 550°C 的还原（燃料）条件下化学稳定，并且在约 950°C 的烧结温度下获得致密陶瓷，类似于 ESB 和其他 d-(Bi,RE)2O3 电解质。流延成型是一种众所周知的低成本大规模生产厚膜陶瓷的技术。由于GDC（~1350C）和ESB（~900C）陶瓷的烧结温度差异较大，不可能通过流延然后共烧结来制备GDC/ESB双层；然而，这对于掺杂 NBT/ESB 陶瓷来说应该是可能的。该项目的目标有两个。首先，优化新发现的基于极性钙钛矿 NBT 的氧化物离子导体系列的电解质特性。其次，测试基于NBT的材料作为基于双层电解质的ITSOFC中电解质成分的适用性。第一个目标将通过对 NBT 进行系统的化学掺杂研究，然后对掺杂 NBT 陶瓷进行晶体学、微观结构和电学表征来实现。这将提供对该系列材料中氧化物离子电导率的结构-性能-成分关系的全面理解。为了实现第二个目标，电解质双层陶瓷将通过在< 1000°C的温度下共烧结掺杂NBT和d-(Bi,RE)2O3的流延层来生产，并在ITSOFC所需的条件下测试其电气和化学性能。这将为这些材料在基于行业标准流延技术制备的双层电解质的 ITSOFC 中的应用提供概念验证。