SusChEM: Ionic Conduction Mechanisms in Low-cost and Rare-earth-free Fast Ion Conductors

快速离子导体是燃料电池、固态电池、气体分离膜和化学传感器等电化学器件的重要组成部分。离子导体适用于这种高性能器件的一个重要标准是在工作温度下的高离子电导率。中温固体氧化物燃料电池是最高效、最清洁的能源转换和存储技术之一，近年来，人们对开发可持续、经济、高导电性的氧化离子导体越来越感兴趣。一种策略是设计不含稀土的快离子导体。在美国国家科学基金会材料研究部固态与材料化学项目的支持下，本项目重点研究离子传导的基本机制，揭示新开发的快速离子导体的化学结构与电导率的关系。本研究结果为合理设计快速氧化离子导体提供了有价值的指导。该研究还开发了独特的表征工具和协议，这些工具和协议将被纳入国家高磁场实验室，并提供给国内和国际用户。参与本项目的学生，包括本科生和一名少数民族女研究生，将获得独特的研究训练机会和指导，以促进其学术生涯。首席研究员的团队通过制作教育视频和在科学活动中进行演示，向公众传播主要发现和技术发展。最近发现了一组新的低成本、不含稀土的快离子导体。有些在中温固体氧化物燃料电池中具有无与伦比的离子导电性。然而，这种高离子导电性的机制尚不清楚。本研究使用钠掺杂的硅酸锶作为模型系统来了解离子如何在这类快离子导体中迁移。该研究包括三个主要任务，包括控制碱性元素掺杂合成硅酸锶，利用高温高分辨率固态O-17、Na-23和Si-29核磁共振探测结构缺陷和离子动力学进行高级表征，以及与核磁共振表征相补充的电化学测量和计算工作，以建立离子电导率与结构缺陷之间的重要联系。

Non-Technical AbstractFast ion conductors are an essential component of electrochemical devices such as fuel cells, solid-state batteries, gas separation membranes, and chemical sensors. An important criterion for ionic conductors to be suitable for such high-performance devices is high ionic conductivity at operating temperatures. In recent years, there has been a growing interest in developing sustainable, cost-effective, and high-conductivity oxide-ion conductors for intermediate-temperature solid-oxide fuel cells, one of the most efficient and cleanest energy conversion and storage technologies. One strategy is to design rare-earth-free fast-ion conductors. With support from the Solid State and Materials Chemistry Program in the Division of Materials Research at NSF, this project focuses on investigating the fundamental mechanisms of ionic conduction and revealing the relationship of chemical structure and conductivity in newly developed fast-ion conductors. The findings from this study provide valuable guidelines for rationally designing fast oxide-ion conductors. The research also develops unique characterization tools and protocols which are to be incorporated into the National High Magnetic Field Laboratory and made available to national and international users. Students assigned to this project, including undergraduates and a female minority graduate student, are provided with unique research training opportunities and guidance to advance their academic careers. The principal investigator's team disseminates the key findings and technological developments to the general public by creating educational videos and performing demonstrations at science events. Technical AbstractA new group of cost-effective and rare-earth-free fast ion conductors has been recently discovered. Some have unparalleled ion conductivity for intermediate-temperature solid-oxide fuel cells. The mechanism for such high ion conductivity is nevertheless unknown. This research uses Na-doped strontium silicates as model systems to understand how ions migrate in this class of fast-ion conductors. The study involves three major tasks including synthesis of strontium silicates with controlled alkaline element doping, advanced characterization with high-temperature high-resolution solid-state O-17, Na-23, and Si-29 NMR probing of structural defects and ion dynamics, and electrochemical measurements and computational efforts complementary to NMR characterizations to establish the important linkage between ion conductivity and structural defects.