Mechanism and Structure of Functional Materials by Solid-state NMR

向清洁可再生能源过渡需要更便宜和更有效的利用和储存能源的手段。这受到太阳能电池和电池等设备中使用的材料的功能特性的限制。为了设计具有更好性能的新材料，我们必须了解材料的结构以及它们在给定应用中的工作方式。特别是原子级结构和化学性质决定了材料的属性和性能。在本项目中，我将使用固态核磁共振（NMR）光谱来识别功能材料的机制和结构。核磁共振测量原子核的磁性，它对原子的局部排列以及原子在从皮秒到分钟的广泛时间尺度上的运动高度敏感。相关实验进一步测量不同原子核的磁矩之间的相互作用，从而能够确定不同物种的空间接近度。NMR特别适合于复杂的、多组分的和/或纳米级的材料，这些材料用其他技术研究是具有挑战性的。我将重点介绍两类重要的材料，混合钙钛矿和MXenes。混合钙钛矿为下一代太阳能电池提供了希望，其效率比目前的硅基光致发光材料更高，生产成本更低。然而，它们的商业化受到其在环境条件下，特别是暴露于光下降解的倾向的阻碍。我将研究光照对钙钛矿材料的结构和动力学的影响，以了解它们如何降解，因此，如何防止降解。这将需要新的实验来测量暴露于光下的设备相关薄膜样品的NMR光谱。MXenes是一类层状2D材料，让人想起石墨烯，可用作电池或气体传感器和隔板。MXene层的表面覆盖着无序排列的官能团，这些官能团很难分解，但它们决定了电池容量和充电速率等功能特性，或气体分离选择性和传感极限。为了优化MXene在这些应用中的性能，我将研究离子和气体分子如何在层之间匹配，以及这如何受到表面基团的影响。先进的核磁共振方法将用于进行这些实验，同时充电/放电的材料原位，并在原位引入气体分子。这些雄心勃勃的实验将揭示限制这两组材料在实际应用中性能的结构因素，从而通过新的配方，加工方法和处理策略指导改进材料的设计。总的来说，这将推动材料走向商业化。此外，方法的发展和专业知识随后可以应用于具有新功能挑战的其他新材料。

The transition to clean renewable energy requires cheaper and more efficient means of both harnessing and storing energy. This is limited by the functional properties of the materials used in devices such as solar cells and batteries. To design new materials with better performance, we must understand the structure of the material and how they work in a given application. In particular, the atomic-level structure and chemistry uniquely determine the material attributes and how well they perform.In this project, I will use solid-state nuclear magnetic resonance (NMR) spectroscopy to identify the mechanisms and structure of functional materials. NMR measures the magnetism of atomic nuclei, which is highly sensitive to the local arrangement of atoms, as well as to motion of the atoms over a wide range of timescales, from picoseconds to minutes. Correlation experiments further measure the interaction between the magnetic moments of different nuclei, enabling spatial proximities of different species to be determined. NMR is particularly well-suited to complex, multicomponent, and/or nanoscale materials, which are challenging to study with other techniques. I will focus on two important classes of materials, hybrid perovskites and MXenes. Hybrid perovskites offer the promise of next-generation solar cells with higher efficiency and lower production costs than current silicon-based photovoltaics. However, their commercialisation is held back by their propensity to degrade under environmental conditions, particularly exposure to light. I will study the effects of light illumination on the structure and dynamics of perovskite materials, to understand how they degrade and, therefore, how to protect against degradation. This will require new experiments to measure the NMR spectra of device-relevant thin-film samples on exposure to light. MXenes are a class of layered 2D materials, reminiscent of graphene, that can be used as batteries or gas sensors and separators. The surfaces of the MXene layers are covered in a disordered array of functional groups which are hard to characterise, but which critically determine the functional properties such as the battery capacity and charging rate, or the gas separation selectivity and sensing limits. To optimise the performance of MXenes in these applications, I will investigate how ions and gas molecules fit between the layers and how this is affected by the surface groups. Advanced NMR methodologies will be used to perform these experiments while charging/discharging the material in-situ, and with in-situ introduction of gas molecules. These ambitious experiments will reveal the structural factors that limit the performance of both sets of materials in real-world applications, thereby guiding the design of improved materials via new formulations, processing methods, and treatment strategies. Overall, this will push the materials towards commercialisation. Moreover, the methodological development and expertise can subsequently be applied to other novel materials with new functional challenges.