Materials World Network: Tailoring Electrocatalytic Materials by Controlled Surface Exsolution

本项目将致力于开发和表征具有钙钛矿结构的高电子导电性掺杂钛酸盐和钒酸盐，用作固体氧化物燃料电池(SOFC)和其他高温电化学器件中高效、燃料灵活和氧化还原稳定的电极的活性电化学成分。虽然我们之前的工作和其他人的工作已经证明了钛酸盐和钒酸盐作为SOFC阳极中的电子传导成分的潜力，但由于它们对氧化反应的催化活性较低，这些电极的性能通常相当差。为了解决这个问题，我们建议使用最近发现的出溶/溶解现象，即当环境条件从氧化改变到还原时，过渡金属(例如，Ni，Pt，Pd)进入和离开钙钛矿晶格。在还原条件下从基质钙钛矿晶格中析出的金属将被用来在电极表面修饰高催化活性材料的纳米颗粒。由于金属暴露在氧化条件下可以溶解回到氧化物中，因此溶解/出溶循环可能被用于再生催化活性，从而产生高度坚固的电极。我们还提出，出溶的金属将在一定程度上锚定在主体晶格上，因此将比通过更传统的方法添加的催化剂更稳定。因此，详细了解出溶/溶解过程的机制、其对氧化物成分和缺陷化学的依赖以及微观结构和电化学性能之间的关系是拟议项目的主要目标。研究小组将由宾夕法尼亚大学的沃斯/戈特小组和圣安德鲁斯大学的欧文小组组成。这两个小组都在固态电化学系统方面拥有广泛的专业知识，在燃料电池研究方面处于世界领先地位，并为合作带来了独特的实验能力(例如，圣安德鲁斯的原位透射电子显微镜和宾夕法尼亚大学的库仑滴定)，并且在使用合作方法实现研究目标方面也有长期的记录

This project will focus on both the development and characterization of highly electronically conducting doped titanates and vanadates which have the perovskite structure for use as the active electrochemical component in efficient, fuel flexible, and redox stable electrodes in solid oxide fuel cells (SOFC) and other high-temperature electrochemical devices. While our previous work and that of others has demonstrated the potential of the titanates and vanadates as the electronically conducting components in SOFC anodes, the performance of these electrodes is generally rather poor due to their low catalytic activity for oxidation reactions. In order to address this problem, we propose to use recently discovered exsolution/dissolution phenomena in which transition metals (e.g. Ni, Pt, Pd) move into and out of a perovskite lattice as the ambient conditions are changed from oxidizing to reducing. Exsolution of the metals from the host perovskite lattice under reducing conditions will be used to decorate the electrode surface with nanoparticles of highly catalytically active materials. Since the metals can be dissolved back into the oxide upon exposure to oxidizing conditions, dissolution/exsolution cycles can potentially be used to regenerate catalytic activity resulting in highly robust electrodes. We also propose that the exsolved metals will have a degree of anchorage to the host lattice and hence will be more stable than catalysts added by more conventional means. Developing a detailed understanding of the mechanism of the exsolution/dissolution process, its dependence on the oxide composition and defect chemistry, and the relationships between microstructure and electrochemical performance are therefore the primary goals of the proposed project. The research team will be composed of the Vohs/Gorte groups at the University of Pennsylvania and the Irvine group at the University of St. Andrews. These groups both have extensive expertise in solid-state electrochemical systems, are world leaders in fuel cell research, and bring unique experimental capabilities to the collaboration (e.g. in situ TEM at St. Andrews and coulometric titration at Penn) and also have a long track record of using collaborative approaches to achieve research goals