Recent developments in MAS DNP-NMR of materials

TL;DR

This paper reviews recent advances in MAS DNP-NMR of materials, highlighting its enhanced sensitivity, technical developments, and diverse applications in understanding material structures at the atomic level.

Contribution

It provides an in-depth overview of high-field MAS DNP-NMR techniques, including hardware, experimental parameters, and applications to various materials.

Findings

Significant sensitivity improvements in NMR using DNP.

Development of tailored polarizing agents for materials.

Application of MAS DNP-NMR to diverse material classes.

Abstract

Solid-state NMR spectroscopy is a powerful technique for the characterization of the atomic-level structure and dynamics of materials. Nevertheless, the use of this technique is often limited by its lack of sensitivity, which can prevent the observation of surfaces, defects or insensitive isotopes. Dynamic Nuclear Polarization (DNP) has been shown to improve by one to three orders of magnitude the sensitivity of NMR experiments on materials under Magic-Angle Spinning (MAS), at static magnetic field $B_0 \ge 5$ T, conditions allowing for the acquisition of high-resolution spectra. The field of DNP-NMR spectroscopy of materials has undergone a rapid development in the last ten years, spurred notably by the availability of commercial DNP-NMR systems. We provide here an in-depth overview of MAS DNP-NMR studies of materials at high $B_0$ field. After a historical perspective of DNP of materials, we describe the DNP transfers under MAS, the transport of polarization by spin diffusion and the various contributions to the overall sensitivity of DNP-NMR experiments. We discuss the design of tailored polarizing agents and the sample preparation in the case of materials. We present the DNP-NMR hardware and the influence of key experimental parameters, such as microwave power, magnetic field, temperature and MAS frequency. We give an overview of the isotopes that have been detected by this technique, and the NMR methods that have been combined with DNP. Finally, we show how MAS DNP-NMR has been applied to gain new insights into the structure of organic, hybrid and inorganic materials with applications in fields, such as health, energy, catalysis,optoelectronics etc.