Mechanism and Structure of Functional Materials by Solid-state NMR

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.