Characterization and optimization of new fluorite-related oxide ion conductors

人们通常认为，导电的固体是通过带电电子在外加电场下的运动来导电的，而导电液体则需要带电离子的运动。然而，情况并不总是如此。液态汞可能是液体表现出金属(电子)导电性的最好例子，而且有多种固体的导电性主要是由于离子迁移。因此，这种固体可以表现出与液体电解液类似的性质和应用。通过O2-离子迁移进行传导的固体的一个重要应用是用作高温固体氧化物燃料电池(SOFC)的电解液，其中电解液分离活性电极材料，可以简单地说是O2和H2。其他应用包括氧气传导膜，例如，它可以通过通过膜传递电流，从不纯源(通常是空气)中生产纯氧。这种装置可用于大规模氧气生产或便携式装置，例如用于医疗目的。为了效率和技术稳定性，低温操作是一项要求，而对在低温下表现出高O2-电导率的新材料的需求为这一提议提供了刺激。我们已经做了一个重要的观察，当某些阳离子部分取代铋氧化物中的铋时，产生似乎是最好的低温各向同性氧化物离子导体(即导电性与方向无关)。现在至关重要的是，我们要对这些材料进行充分的表征，以便：i优化它们的性能；ii全面检查(并可能提高)它们在低温下长期使用的稳定性；iii探索它们在实际应用中的潜力；iv探索我们观察到的其他系统的可能性。尤其是，我们需要探索我们已经合成的材料的详细结构，特别是被取代到铋氧化物骨架中的离子周围的局部结构，以及对实际设备中的应用非常重要的表面性质。我们还需要更好地了解适用于这些材料中O2-迁移的机制，以便使观察到的改进的电导率合理化。这一目标不能通过实验来实现，而需要使用理论模型。因此，该提案将把来自不同研究中心的四个高质量研究小组合并在一起，每个研究小组将在实现以下目标所必需的领域提供独特的国际领先专业知识：伯明翰/合成、结构评估；帝国理工学院/表面性质和O2-离子扩散参数；谢菲尔德/电导率测量；在多变的大气条件下进行电导率测量；探索O2-迁移机制的浴池/理论模拟，并提供实现类似或更好性能的其他可能方法的信息。

It is commonly assumed that solids which conduct electricity do so via the movement of charged electrons under an applied electric field, and electrically conducting liquids require the movement of charged ions. However, this is not always the case. Liquid mercury provides, perhaps, the best example of a liquid showing metallic (electronic) conduction, and there are a variety of solids whose conductivity is primarily due to ionic migration. Such solids may therefore show similar properties, and applications, as liquid electrolytes. An important application for solids which conduct via the migration of O2- ions is as electrolytes for high temperatures solid oxide fuel cells, SOFCs, where the electrolyte separates the active electrode materials, which may simply be O2 and H2. Other applications include O2- conducting membranes which can, for example, be utilised for the production of pure oxygen from impure sources, typically air, by passing a current through the membrane. Such devices could be used for large scale oxygen production or in portable devices, e.g. for medical purposes. For efficiency and technological stability, low temperature operation is a requirement, and the need for new materials which show high O2- conductivity at low temperatures provides the stimulus for this proposal. We have made an important observation that certain cations, when partially substituting Bi in bismuth oxide, produce what appear to be the best low temperature isotropic oxide ion conductors (i.e. the conductivity is independent of direction). It is now vital that we fully characterise these materials in order to:i optimise their properties;ii fully check (and possibly improve) their stability to long term usage at low temperatures;iii explore their potential for real applications;iv explore the possible extension of our observation to other systems.In particular, we need to explore the detailed structure of the materials we have already synthesised, especially the local structure around the ions substituted into the bismuth oxide framework, and the surface properties which are important for applications in real devices. We also need to have a better understanding of the mechanism applicable to the O2- migration in these materials, in order to rationalise the improved conductivity observed. This objective cannot be achieved experimentally, but requires the use of theoretical modelling. The proposal therefore will bring together four high quality research groups from different research centres, each of which will provide unique, internationally leading expertise in the areas necessary to achieve the objectives:Birmingham / synthesis, structure evaluation;Imperial College / surface properties and O2- ion diffusion parameters;Sheffield / conductivity measurements under variable atmospheric conditions;Bath / theoretical simulations to explore the mechanism of O2- migration and provide information on other possible methods to achieve similar, or better, properties.