Goal

To understand how materials work and how that depends on their atomic-scale structure, guiding the design of better materials for a given application.

Solid-state NMR

Michael’s research benefits from the use of solid-state NMR to characterise the structure and dynamics of complex functional materials. Traditionally, material characterisation has focussed on a static picture of bulk structure, because this is amenable to diffraction-based techniques; often, however, it is the local structure at surfaces and interfaces, as well as dynamic changes in the structure, that determine the functional properties. Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy is ideally suited to study the mechanism and structure of functional materials as a local, element-specific, probe of chemical structure, dynamics, and electronic properties. Solid-state NMR can also be used to study amorphous, nanoscale, heterogeneous, and/or low-dimensional materials, which are becoming increasingly important for modern devices. The solid-state NMR spectrometers are hosted within the Warwick Solid-state NMR Group (pictured right).

Hybrid Perovskite Photovoltaics

Large-scale adoption of photovoltaic energy is primarily limited by cost, as market-leading silicon cells require expensive high-temperature processing and purification. Hybrid organic–inorganic perovskites (APbX₃, where A⁺ is a small organic cation and X⁻ is a halide) offer the possibility of cheap, scalable devices owing to the low cost of raw materials and solution processability. Following a decade of extensive research, conversion efficiencies have increased from 3.8% to >25%, exceeding that of polycrystalline silicon. However, the long-term structural instability of hybrid perovskites under conditions of heat, moisture, and light irradiation currently prevent their commercialisation. Solid-state NMR is ideally suited to study a range of phenomena in hybrid perovskites, including cation/halide substitution, phase transitions, cation dynamics, surface passivation, and degradation.

MXenes

MXenes are a class of 2D transition metal carbides and nitrides with unusual properties, combining metallic conductivity with hydrophilic surfaces. Since their discovery in 2011, more than 30 different MXene phases have been synthesised by varying the metal (M), carbon/nitrogen (X), and the number of layers (n) in the general formula M_n+1X_n. MXenes are synthesised by etching the “A” element from the corresponding 3D MAX phase (e.g., Ti₃C₂ is produced from Ti₃AlC₂); however, the surfaces are not bare but rather terminated by different functional groups (e.g. -OH, -O, -F). These surface groups critically determine the performance of devices but are hard to characterise. Michael is interested in studying MXene surface groups and how they interact with intercalated ions and gas molecules for applications as supercapacitors (ultra-high power batteries) and gas sensing and separation.

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