Materials with specific electrical, optical or chemical properties often derive their special functions from small perturbations in their composition or structure. Thus, rational design of new functional materials demands sensitive and versatile determination of structural and compositional properties, a very difficult goal not presently available. The overarching goal of the MIDNP project is to develop a novel route for Magic-Angle Spinning Dynamic Nuclear Polarization (MAS-DNP) as an enabling methodology in materials science, introducing new opportunities for investigating and designing functional materials.
Solid State Nuclear Magnetic Resonance (ssNMR) spectroscopy is an excellent probe for local order/disorder, but unfortunately its sensitivity is limited. DNP, a process whereby the large electron spin polarization is transferred to the nuclear spins, had greatly expanded the range of materials systems and questions that can be probed by ssNMR. However, it commonly relies on the use of exogenous nitroxide radicals, thereby limiting its utilization in materials science to nonreactive surfaces.
In MIDNP we develop an alternative approach, utilizing paramagnetic dopants as endogenous polarization agents in the bulk. To effectively harness the electron spin polarization of the dopants for higher sensitivity, we: (a) addressed challenges such as the effect of bonding, spin interactions and relaxation on DNP via a mechanistic study of carefully selected dopants in energy materials; (b) Developed new techniques for NMR spectral assignment and explored alternative DNP mechanisms for paramagnetic solids; (c) Expanded the approach for sensitizing the detection of surfaces and interfaces and elucidate the critical role of surface chemistry in the efficacy of energy storage materials. (d) Developed a new structural tool for interfaces by combining sourced of polarization in DNP: exogenous radical which selectively increase the sensitivity to outer surface layers and endogenous DNP from metal ions which provide sensitivity in a selective manner to the inner layer.
The methodology developed as part of the MIDNP project and its applications has already provided critical insight into the structure and composition of materials with relevance to energy storage and conversion systems. Based on these insights, and future studies that will implement the developed methodology, on other materials systems, we expect MIDNP will contribute to the development of new and improved energy storage and conversion materials. Such materials are essential for developing long lasting and efficient systems for utilization of sustainable energy resources.
