Contributed
Towards DNP-NMR in conductive and semi-conductive materials: Effects of conductivity on the DNP efficacy

Conductive and semi-conductive materials are the main building blocks of advanced technologies, such as energy storage and conversion systems, that are essential for our modern life. Improvement in materials performance and development of new ones relies on our ability to obtain structure-function correlation. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy is well suited for providing structural information at the atomic level, especially when it is equipped with high sensitivity gained from the electrons spin by Dynamic Nuclear Polarization (DNP). However, to date, the majority of systems studied by DNP were non-reactive and diamagnetic materials such as proteins and insulating solids. The polarization in these cases comes from exogenous nitroxide radicals, which are added to the solid of interest. This approach cannot be simply extended to conductive and reactive materials systems. In these types of materials the application of DNP is challenged by: (i) Possible interaction between the radicals solution and the reactive interfaces and (ii) the effect MW irradiation used for efficient polarization transfer on delocalized free electrons within the materials.

Here we explore the effect of conductivity on the DNP efficacy, using a series of carbons with increasing electron conductivity and determine the feasibility of exogenous DNP with nitroxide radicals. We observed that with increasing the conductivity, the signal enhancement drops significantly. These effects were ascribed to heating of the sample due to the interaction between the conduction electrons and the MW irradiation. Furthermore, we demonstrate endogenous DNP, utilizing unpaired electrons within the carbons. These preliminary results can, in the future, be used to extend DNP-NMR to study conductive carbon allotropes, that are integrated into a wide range of applications.