Research Activities @MagRes
Our group’s research focuses on developing new magnetic resonance spectroscopic methods and techniques to elucidate structural and dynamical details of environmental and renewable energy materials, including soil, cement-based materials, semiconductors for solar energy harvesting, catalysts for biomass energy conversion reactions, and electrolytes.
While solid-state NMR has unique capabilities that allow the non-invasive characterization of systems regardless of their crystallinity, the low sensitivity of the technique is still a major challenge. We address the sensitivity challenge with a multifaceted approach by combining hyperpolarization techniques, new hardware designs, sample preparation methods, and radio-frequency pulse sequences. Thus, our group is an interdisciplinary research group in which both experimental and theoretical projects are being pursued.
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NMR Theory and Methods
New RF pulse sequences and NMR crystallography
Solid State NMR is still in search of new spin probing techniques to excite or suppress particular spin-spin interactions and focuses on dynamics measurement. MagRes group focuses on searching for newer radiofrequency pulses that synchronize RF pulses with spatial rotations and produce intended results. MagRes also focuses on Crystallographic studies along with NMR and correlating them to enrich the field, named NMR-Crystallography.
Relaxation Theory in NMR
The dynamics of spin systems have been one of the most interesting topics from the beginning of the Quantum age. Theoretical explanations along with magnetic resonance experiments are the latest way to explore the spin dynamics of various systems in Material research, Biology, Quantum materials, etc. Now relaxation of spins can be a friend but also be a foe in both EPR and NMR spectroscopy. Our aim is to understand relaxations and prescribing new techniques in magnetic resonance spectroscopy. Also, the effect of paramagnetic centers on spin dynamics is aimed to describe with theoretical prescriptions.
Different interactions are always a part of magnetic resonance spectroscopy. We are focused on making new RF pulses for decoupling and enhancing the sensitivity for the information of interest.
Dynamic Nuclear Polarization through defect centres of diamond
Dynamic Nuclear Polarization (DNP) alleviates the sensitivity problem of Nuclear Magnetic Resonance (NMR) by transferring the spin polarization of the relatively more sensitive electron spins (e) to the nuclear spins (n) of interest. DNP requires paramagnetic centers, either intrinsic to the system or added extrinsically, coupled with the nuclear spins and microwave irradiation near EPR frequencies of the paramagnetic centers to drive the polarization transfer. The most commonly employed DNP experiments are performed at ~100K using gyrotrons as high-power microwave sources. Several DNP mechanisms, like the Overhauser Effect, Solid Effect, Cross Effect, etc., are used for several systems depending upon experimental conditions like the field, microwave power, EPR properties, and radicals. However, the need for cryogenic temperatures to combat fast electron spin relaxation rates restricts the applicability of DNP. Moreover, the high cost of gyrotrons, high maintenance, and facility requirements make it a highly specialized equipment limited to few labs.
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The paramagnetic diamond defects, including the NV-centers, are promising alternatives to the conventional radical-based polarizing agents due to their relatively longer coherence times at room temperature. Our approach is to design a DNP mechanism effective over a longer e-n distance, using microwave pulses and coupled electron spin systems (NV-NV, NV-P1, or NV-external electron spins) rather than isolated defect centers.
Material Science NMR
Study of soil organic matter (SOM)
Soil is a vital component of our ecosystems that plays a key role in maintaining the balance of carbon in the environment. The carbon stored in soil organic matter (SOM) is known as soil organic carbon (SOC). Studies have shown that numerous factors, including human activities, have impaired soil health, i.e., its capacity to participate in the ecosystem, as manifested in declining SOC over the past decades. Therefore, a deeper understanding of soil chemistry is imperative for a sustainable future of life on earth.
The presence of multiple phases of matter and interactions make the soil an extremely complex composition to study. We chose solid-state NMR as the primary tool to address this challenge. We aim to improve solid-state NMR methods using advanced numerical approaches and new instrumentations to study SOM and its dynamics in detail.
Study of solid elctrolyte materials using NMR
Energy storage devices (ESDs) with high safety, long durability, low cost, high energy, and power density are absolutely necessary to replace fossil fuels with renewable energy and combat one of the greatest threats to the planet: climate change. Currently, lithium-ion batteries (LIBs) are the most common ESDs. However, the problems of flammability, dendritic growth, low energy density, and limited operating temperature range limit their usage to a small scale.
LIBs with solid electrolytes (SEs) are promising alternatives to address the problems above, but there are two major challenges with those: (i) High resistance at the electrode-electrolyte (solid-solid) interface and (ii) low ionic conductivity in the SEs. We will use solid-state NMR that is not restricted by these obstacles and can directly probe the key elements such as 1H, 7Li, 13C, 14N, 19F, etc., frequently present in the solid electrolyte material.
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Our aim is to improve the sensitivity by developing specific NMR pulse sequences targeting battery materials and using hyperpolarization methods that allow a sensitivity boost by two orders of magnitude. We will merge the expertise in NMR instrumentation, pulse sequence development, and cell design for in-situ battery studies to gain deeper insight into the interactions at the interface as well as in the electrolyte that determine the efficiency of the battery.
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